Living stones: plants that look like rocks

If you take a walk in some deserts, you will find some very special stones: “living stones”. Logically, rocks and stones are non-living things, so a closer look would reveal you that these are plants that have taken on the appearance of stone. Do you want to know why?

By the name of living stones or stone plants, we find different genera of succulent plants. As you already know, succulent plants are those that have a large water storage capacity. Some of their structures, usually the leaves or stem, have a fleshy appearance due to this specialization to store water. These reserves allow them to survive in very arid environments or periods of water shortage. A well-known example of succulent plants with fleshy leaves is the Aloe vera plant, and an example of plants with succulent stems, cactuses.

Aloe Vera plant, with a carved leaf in the foreground where the succulent part is seen. Photo: Indianmart

By the name of stone plants we find different species of different families. The best known are those belonging to the genus Lithops, from Africa, since they are grown as ornamental plants. Other plants that look like stones are the species Dioscorea elephantipes (elephant’s foot) and Fredolia aretioides, both African. In the Andes we find Azorella compacta.

Camouflaged Lithops between pebbles. Photo: Xocolatl

LITHOPS SP. 

Within the genus Lithops we find several species, all with the appearance of small stones or pebbles.

As we know, to survive in arid environments plants can accumulate water inside. In addition, they reduce the contact surface of their leaves with air, to minimize the loss of water through perspiration. The most extreme case are cactuses: they have tiny and very hard leaves: the spines.

Cacti’s spines are modified leaves and the green part corresponds to the fleshy stem. Photo: freestockcenter

In the case of Lithops (from the Greek: “lithos” -rock- and “ops” -face-), they only have outside the ground a pair of succulent leaves of 2 to 5 centimeters, with the appearance of small stones, since they also have small white spots on their surface. This stone appearance also helps them to go unnoticed by their predators. This strategy (being confused with the environment) is known as crypsis.

Lithops in a pot in different stages of growth. We can see the two leaves of each plant. Photo: yellowcloud

Actually, these spots are translucent zones, without chlorophyll, so that light can penetrate towards the rest of the plant, which is flat and remains underground. Between the two mature leaves, we find a tissue where the growth of the pair of new leaves occurs. Once the two new leaves have emerged from the center of the plant, the two old ones wither and die.

Longitudinal section of a Lithops. We see the central tissue where the new leaves will grow, the succulent translucent tissue, the photosynthetic green tissue and the translucent tissue through which the light enters (upper epidermis). Photo: C T Johansson

REPRODUCTION OF LITHOPS

Lithops reproduce asexually (cuttings) and sexually (seeds). In spite of this, reproduction by cuttings is only possible if the plant has divided naturally. If we cut and plant before it has divided itself, it will not develop as a new plant. That is why mainly the reproduction is by seeds, which are produced by a flower that emerges between the two leaves of the plant. Take a look to this 7 day- time lapse of the blooming of a Lithops:

Its curious appearance, beauty and easy maintenance, have made Lithops a decorative plant in homes and gardens.

ELEPHANT FOOT

Dioscorea elephantipes, known as elephant’s foot, turtleback or Hottentot bread, is a deciduous climber plant. Its tuberous stem is partially buried, full of fissures and covered by a hard bark. This gives it a rocky look, similar to the skin of an elephant or the shell of a turtle, as its popular name suggests. In addition, this plant accumulates large quantities of starch, so it is also known as Hottentot bread.

Tuberous stem of Dioscorea elephantipes with dry shoots un its center. Photo: Hectonichus

In winter, green shoots appear with yellow flowers, that will grow until they die in summer. At this time the plant goes through a dormancy period and it will hardly need water until the appearance of the following shoots.

Elephant’s foot in summer. We see shoots with leaves. Photo: Natalie Tapson

Unlike Lithops, the elephant foot can reach one meter in height and three in circumference, although its growth is very slow. But just like Lithops, its shape tends to the sphere. This is because the sphere is the geometric shape that holds more volume offering less surface to the outside. The plant can grow minimizing the surface of contact with the air, thus reducing the loss of water by perspiration.

If you think about the amount of approximately spherical forms that we find in living beings (eggs, seeds, fruits, animals, etc.), it may be due to this reason: maximum volume (of nutritional reserves, of corporal volume…) using a minimum surface (less transpiration, less loss of heat, less surface to offer to the predators…). If you want to delve into this subject (and other shapes) it is an idea of ​​the late Jorge Wagensberg, who deals in his book The rebellion of forms and inspires a permanent exhibition at the CosmoCaixa in Barcelona.

FREDOLIA ARETIOIDES 

Fraedolia aretioides going unnoticed in the Sahara desert. Photo: Rafael Medina

Fredolia aretioides, which lives in the north of the Sahara, uses the same strategy as the elephant’s foot plant: a spherical shape to avoid the loss of water. Unlike the elephant’s foot, it does not have a hard crust, and unlike Lithops, it has more than two leaves. The plant has many hardened stems and leaves with compact growth. These leaves are a greenish-grayish color, which gives it a more rocky appearance, going completely unnoticed among the rocks of the northern desert.

Fredolia aetioides in detail. We can see a lot of tiny leaves making a compact spherical shape . Photo: Rafael Medina

AZORELLA COMPACTA

Azorella compacta, llareta or yareta distributes throughout South America, specifically in the Andes, from 3,200 meters to 4,800 meters above sea level. It is perfectly adapted to the great insolation that the soil receives at this altitude, which also, in the Andean Puna, is black or gray due to its volcanic origin. This means that at ground level the air temperature is one degree or two higher than the ambient temperature.

Yareta in Andes. Photo: Pedro Szekely

Despite being from another family and growing in a different environment than Fredolia, yareta has evolved the same strategy as it to avoid the loss of water: round shape, compact stems and small and hardened leaves. Like the previous species we have seen, it also reproduces by seeds and its flowers are yellow-greenish.

CONCLUSION

We can conclude that, although from different origins, evolution has led all these plants to solutions similar to water scarcity, to withstand high insolations and to avoid losing temperature during the night: endowing them with practically spherical shapes to reduce their relationship between surface and volume. In addition, this adaptation is complemented by the reduction of the number or size of the leaves and the accumulation of water and nutrients inside.

 

Cover photo: ellenm1 (Flickr)

The importance of biological collections

Biological collections are cornerstones for the study of biodiversity and an almost endless source of scientific information. Many are those within the social networks who demand scientists to stop using ‘classical’ biological collections as they are seen as primitive tools that promote animals and plants extinctions.

We explain you why this statement is incorrect, which types of collections do exist and which are their most relevant functions.

It is more than probably that the first thing it comes to mind when you hear someone talking about biological collections are hundreds of animals or plants dried, pinned and placed inside boxes by a fanatical collector. Yes, this type of collections exists. However, and without demonizing them (since these collectors can be very useful for science), this is not the type of collections we want to talk about and, of course, not the only one that exists.

Biological collections are systematized repositories (well identified, classified and ordered) of a combination of any biological material. Most of these repositories are deposited in natural history or science museums, but also in universities, research centers or even totally or partially in private collections.

ICM’s (Institute of Marine Sciences) Biological Reference Collections, in Barcelona. Picture by Alícia Duró on ICM’s web.

Some drawers of the Australian National Insect Collection. Picture by the Australian National Insect Collection.

Types of collections

Even though the concept of biological collection is something quite new, the collection and classification of biological material started some centuries ago with the first animals and plants collected by zoologists and botanists.

Nowadays, the term of biological collection has acquired a broader meaning:

• Cryogenic collections

Storage of living biological material in frozen state under the assumption that it will retain its viability and normal functioning when being thawed after a long period of time. Cryogenic collections are typically used to store cells, tissues and genetic material. And even though science fiction has given us many fantastic ideas, the truth is that this method is very rarely used for preserving entire organisms.

• ‘Classical’ biological collections

They essentially include collections of zoological museums (entire specimens or some of their parts) and herbaria (plants), among others. Some of these collections go back over more than two centuries, so ‘classical’ biological collections are considered the oldest within all types of collections. And also, one of the most valuable.

Collection of inquiline cynipids or gall wasps . Source: Irene Lobato Vila.

Most of these collections are deposited in museums or research centers and, excepting some particular cases, able to be required and examined by the scientific community as it pleases. A lot of private collectors collaborate with these institutions by transfering their specimens, which is quite common among insect collectors.

Drawers from the National Museum of Natural History, Washington D.C., Smithsonian Institution, containing thousands of insect specimens. Source: Irene Lobato Vila.

It is worthwhile remembering that transferring is subjected to an exhaustive revision and done only under contract, so institutions do not accept specimens obtained directly by the collector from illegal methods (e. g., poaching or wild animal trading).

• Collections of biological information online

Repositories of biological information online. This type of collections has gained a lot of importance during the last years since it allows to share biological information of interest to science and technology immediately around the world. The most consulted online databases are those containing molecular data (proteins, DNA, RNA, etc.), which are necessary for phylogenetic studies and to make ‘trees of life’. Some of these databases are:

• GenBank
• BOLD Systems
• Protein Data Bank

Other types of very consulted webs are the online databases of museum collections (which are of very importance to preserve massive amounts of data deposited in this institutions; remember the case of the Brazil National Museum fire) and webs of citizen science projects and collaborations, where either experts and amateurs provide information of their observations (like Biodiversidad Virtual).

Biological collections can be also classified according to their function: scientific collections (research), commercial collections (cell cultures for medicine, pharmacy, etc.) and ‘state’ collections (those created and managed for the sake of the state, like botanical garden, in order to preserve the biodiversity of a region and to promote its study and outreach).

The term of biological collections also embraces the biobanks, that is, collections exclusively containing human samples for biomedical studies. However, we will not go farer with this term.

Why are classical biological collections so necessary?

Biological collections and, especially, classical biological collections, are essential for biodiversity conservation. And no, they are not a direct cause of species extinction: the number of collected specimens is derisory compared with those lost as a consequence of pollution and habitats loss, and collections are carried out following several rules, always making sure to not disturb populations and their habitats.

Although it is true that pictures and biodiversity webs are a very useful tool for the study of worldwide biodiversity, unfortunately they are just a completement of physical collections.

So, why are these classical and physical collections so important?

• They are a very valuable source of genetic material that can be obtained from stored samples and used in molecular studies. Thanks to these studies, we can approach to the origins and relationships of living beings (phylogeny), know their genetical diversity and the speciation mechanisms that lay behind species differentiation, or even to improve strategies to conserve them (e. g., in reintroduction and conservations plans).

• They are a perpetual reference for future scientists. One of the basic pillars of zoological and botanical collections are the type specimens or type series: those organisms that a scientist originally used to describe a species. Types must be correctly labelled and stored because they are the most valuable specimens within a collection. The type or types should be able to be examined and studied by all scientists and used by them as a reference for new species descriptions or for comparative studies, since original descriptions can sometimes be insufficient to characterize the species.

Paratype insect (specimen from the type series) properly labelled and deposited in the entomological collection of the National Museum of Natural History of the Smithsonian Institution, in Washington D.C. Source: Irene Lobato Vila.

• Regarding the previous point, classical collections allow to study the inter and intraspecific morphology (external and internal), which is sometimes impossible to assess only with pictures.

• Classical collections contain specimens collected from different periods of time and habitats, including extinct species (both from a long time ago and recently due to the impact of human activity) and organisms from endangered ecosystems.  As habitat destruction continues to accelerate, we will never have access to many species and the genetic, biochemical, and environmental information they contain unless they are represented in museum collections. The information these samples provide is essential to investigate how to slow or mitigate the negative pressure on still extant species and ecosystems.

• They provide us past and present information about geographic distribution of different organisms, since each of them is usually stored together with data about its locality and biology. This kind of information is very useful both for ecological and evolutive studies, as well as for resource management, conservation planning and monitoring, and studies of global change.

• They are an important tool for teaching purposes and popular science, since people get directly in touch with samples. Pictures and books are undoubtfully essential for outreaching, but insufficient when they are not complemented with direct observations. Both visits to museums and field trips are basic tools for a complete environmental education.

At the end of the course each year,  thousands of students visit the collections of the National Museum of Natural History in Washington D.C. Some of them may even visit the scientific collections. Source: Irene Lobato Vila.

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Do you still think biological collections are unnecessary after reading this post? You can leave your comments!

Crown shyness: trees that don’t touch

When you walk through the forest or the city, do you usually look up? The usual thing is to look at where we are going or where we put our feet, but if you find yourself in the middle of nature, do not forget to observe the trees, perhaps you find yourself with an image as beautiful as the cover of this post: you are observing the crown shyness.

A BOTANICAL PHENOMENON

Less than 100 years ago, back in 1920, a botanical phenomenon that give us beautiful and impressive images of certain forests was observed for the first time. In 1955, the botanist Maxwell R. Jacobs, described this phenomenon as “crown shyness” after studying various populations of eucalyptus. The crown shyness is also known as canopy disengagement, canopy shyness or intercrown spacing.

The furrows of sky that makes the crown shyness. Photo: Tom Cowey

This phenomenon consists in a limited growth of the canopy of the trees, in such a way that the leaves and branches of adjacent trees do not touch each other. This produces figures and patterns with the sky in the background when the trees are observed from the ground.

The canopy disengagement, among other themes, is explored in the documentary Once Upon a Forest.

WHY CROWN SHYNESS OCCURS?

The scientific community has not yet reached a consensus that explains the mechanism that gives rise to this phenomenon. A total of three hypotheses have tried to explain the crown shyness:

1. Friction hypothesis

The initial hypothesis of Maxwell R. Jacobs (currently barely accepted by the scientific community) explains that the friction of some branches with others, when the wind hits them, would limit the growth of the branches to avoid touching the neighboring trees, due to the damages produced by the abrasion.

2. Allelopathy hypothesis

The most supported hypothesis currently indicates that crown up  has an allelopathic origin.

In botany, allelopathy is any effect that one plant transmits to another through the production of different chemical compounds, either causing a positive or negative effect on the other plant. These compounds are the so-called allelochemicals. In other words, plants and trees communicate with each other by chemical signals. This relationship occurs more frequently between trees and plants of the same species, although it also occurs between different species. To know in depth the process of allelopathy, we invite you to read the post Communication among plants: allelopathy.

Photo: airwii

3. Photoreceptors hypothesis

In addition to chemical signals, phytochrome photoreceptors (sensors of light capable of detecting the area of distant red light) possessed by trees and plants allow them to perceive the proximity of other individuals. Another type of photoreceptor detects blue light, which produces in plants and trees the avoidance of shadows produced by other individuals.

Plant photoreceptors and photoresponses. Credit: Christian Fleck

As a whole, the signals captured by these photoreceptors would provoke the response of the tree to move away from the adjacent one, which would allow it to obtain a greater quantity of light, which is essential for photosynthesis.

ARE ALL TREES “SHY“?

Crown shyness has been observed in certain European oak and pine species and tropical and subtropical species, such as some eucalyptus, species of the Dryobalanops genus, Pinus contorta, Avicennia germinans, Didymopanax pittieri, Clusia alata, Celtis spinosa, Pterocymbium beccarii, Picea sitchensis and Larix kaempferi.

Arboreal canopy of Dryobalanops aromatica in Kuala Lumpur. Photo: Patrice78500

In other species, the tops of the trees come to touch and even cross their branches, although the canopy (habitat that includes the tops of the trees) does not usually mix completely.

HYPOTHESIS ON THE ADVANTAGES OF THE CANOPY SHYNESS

The evolutionary sense of the timidity of the glass remains unknown, although botany has launched several hypotheses:

• It allows a greater penetration of light in the forest to perform photosynthesis more efficiently.
• It avoids damaging the branches and leaves when hit against each other in case of storm or gusts of wind.
• It prevent diseases, larvae and insects that feed on leaves from spreading easily from one tree to another.

Ants build structures with their own bodies to move from one leaf to another. Photo: Rose Thumboor

For now, it seems that crown shyness is due to a relationship of collaboration between species for survival, rather than a competition (the popularly known as the “survival of thje fittest”). We will have to wait for future studies to shed a little more light on this still unknown phenomenon.

Flowers in the kitchen

Although flowers can be part of our diet, there are the plants parts less considered in gastronomy. Apart from providing color and beauty to our meals, flowers can enrich our diet with different nutrients and textures. In this post, we talk about what kind of flowers are used in different cultures kitchens and what benefits they can bring.

ROOT, STEM OR LEAVE EATING?

Maybe you have never asked yourself about what part of the plant you are eating when you consume a potato, a lettuce, a tomato or a sunflower seed but all cited vegetables are different plant organs with distinct properties and functions. Potatoes, carrots, sweet potatoes, beets and mandioques are roots or tubers and contribute our organism with many nutrients. One of the functions of the roots is to accumulate reserves for the leaves and flowers development, so these organs constitute a valuable source of high-energy carbohydrates and vitamins. On the other hand, the greenest and crispiest vegetables in our diet like lettuce, spinach and chard are leaves and its function is to do the photosynthesis. His contribution to our diet is very beneficial because they contain lots of fiber, vitamins and minerals. Following our plant tour we can continue with fruits, sometimes called vegetables such as tomatoes, zucchini, peppers, eggplants and beans. The fruits include highly rich nutrients because have their function is to accumulate nutrients for seed germination. They contain fiber, sugars, minerals and a large intake of vitamins. Finally, many also consume seeds and nuts, such as almonds, walnuts, pine nuts and peanuts. These feed us with beneficial fats and essential amino acids, fiber and vitamins.

There are other plants parts less frequently consumed, but all plant organs can have a profit! The stem or trunk is usually too fibrous and hard to eat although some species are made of trunk such as cinnamon (Cinnamomum verum).

And flowers? What role do they have in our diet? The showy and most ephemeral plants part have been used throughout history and cultures to feed us or their uses are limited to ornamentation?

EATING FLOWERS

In fact, we regularly consume flowers although perhaps we do not perceive. In the Mediterranean diet, one of the most popular vegetable is a flower: the artichoke (Cynara scolymus) is an inflorescence from which we only consume the basis of the floral bracts and the receptacle when it is not yet mature. Also capers (Capparis spinosa) are buds used in vinegar in the preparation of many Mediterranean dishes. When you eat broccoli or cauliflower (Brassica oleracea) you are also eating the immature flowers of these plants.

Capers buds to consume and an open caper flower. Source: PresidenciaRD by Flickr.

Another common flower in the Mediterranean, with a very special taste is Aphyllanthes monspeliensis. Its flowers are very sweet and is a delight to eat them while you walk through the countryside. Also elder flowers (Sambucus nigra) are used to prepare delicious and very aromatic bunyols at Spain. The elder flowers are anti-inflammatory, antiseptic and diuretic and they act against colds, fever and bronchitis.

In other cultures, the flowers are used for flavoring desserts and sweets. For example at Turkey and Iran, rose water (Rosa sp.) is used to make the famous lokum or Turkish delight.

Turkish delights aromatized with rose water. Source: Pinterest.

Other flowers used in infusion are hibiscus flowers (Hibiscus sabdariffa). Only sepals are used to prepare an iced tea with diuretic properties, very popular in Jamaica but also common in Mexico and other countries in Central America.

Hibiscus dried sepals. Source: Commons Wikimedia.

The violet flower (Viola odorata) is also very sweet and aromatic. It is used to make a famous candy from Madrid, manufactured from 1915, with calming properties. Viola flowers can also be sued to make pies, jellies and ice cream.

Violet candies typical from Madrid. Source: morenisa.blogspot.com.

The zucchini flowers (Cucurbita pepo) after the stamens have been removed, are used in Italy for a very original pizzas. Similarly, in Greece and Turkey, they eat pumpkin flowers (Cucurbita maxima) batted or stuffed and fried. They are also used in Mexico to make quesadillas.

Zucchini flowers pizza. Source: Gourmand Asia.

Flowers have been used at kitchen from Roman and Greeks time. They used flowers in salads, like mallow (Malva sylvestris), that has soothing and healing properties in infusion.

Flowers add color, texture and beauty to our meals while they can also provide taste contrasts, as they are not always sweet and soft. For example, cornflower (Centaurea cyanus) and nasturtium (Tropaeolum majus), both edible flowers have a spicy taste and borage (Borago officinalis) reminds cucumber and can be used in salads, soups or drinks. The chives flowers (Allium schoenoprasum) are often used to add a very special taste of garlic at salads and soups.

Nasturtium flower. Source: David Goehring by Flickr.

Borage flower. Source: Commons Wikimedia.

Some spices come from flowers or organs flower. Saffron (Crocus sativa) is the female organ (style and stigma) of this species bloom, giving color and flavor to spanish paellas. Its cultivation is extremely delicate and expensive: 200 thousand of flowers or 600 thousand of pistils are needed to produce 1 kg of saffron. Spain is the world’s largest producer. Cloves (Syzygium aromaticum), originally from Indonesia, are in fact dried buds of a tree that can reach 12 m high. Its strong smell can help in producing a natural insecticide prepared with cloves infusioned with distilled water and alcohol.

Saffron flowers with its typical red pistils. Source: pixabay.

Maybe not all the flowers mentioned are affordable but we encourage you to include flowers in your meals while learning more about plants cooking them.

REFERENCES

Graziano, X. 2010. Almanaqueo do Campo. Panda Books, Sao Paulo, Brasil.

Metal hyperaccumulation in plants

During million years the evolution leaded plants to develop different strategies to defence from natural enemies, giving rise to an evolutionary weaponry war in which the survival of ones and others depends into the ability to beat the other’s adaptations. It is in that scenario where the high-level accumulation of heavy metals in plants plays an important role.

INTRODUCTION

Boyd (2012) commented that plant defences can be grouped in different categories:

• mechanic: thorns, coverage, etc.
• chemical: different organic and inorganic components.
• visual: crypsis and mimicry .
• behavioural: related with phenology’s modification.
• and associative: symbiosis with other organisms, such is the case of the genus Cecropia, which has stablished a symbiotic relationship with ants of the genus Azteca, who protects these plants – to know more: Plants and animals can also live in marriage-.

Mechanic defence with thorns (Author: Karyn Christner, Flickr, CC).

It is known that chemical defence is ubiquitous, and thus, a lot of interactions among organisms can be explained for this reason. In this sense, some plants contains high levels of certain chemical elements, frequently metals or metallic components, which plays an important role in the defence, these plants are the heavy metal hyperaccumulating plants.

Heavy metal hyperaccumulating plants and their main characteristics

This plants belong to several families, thus hyperaccumulation is an independent acquisition occurring different times during the evolution. In all cases, hyperaccumulation allowed the ability to grow soils with high levels of heavy metals and to accumulate extraordinary amounts of heavy metals in aerial organs. It is known that the concentration of these chemical elements in hyperaccumulating plants can be 100 – 1000 times higher than in non-hypperaccumulating plants.

Generally, chemistry describes heavy metal as transition metals with atomic mass higher than 20 and with a relative density around 5.  But, from a biological point of view, heavy metals or metalloids are elements which can be toxic in a low concentration. Even though, hyperaccumulating plants has become tolerant, i.e., they hypperacumulate this heavy metals without presenting phytotoxic effects (damage in plant tissues due toxicity).

In this sense, there are three main characteristics typically present in all hyperaccumulating plants:

• Increased absorption rate of heavy metals.
• Roots that perform translocation more quickly.
• Great ability to detoxify and accumulate heavy metals in sheets.

Thus, hyperaccumulating plants are prepared to assimilate, translocate and accumulate high-levels of heavy metals in vacuoles or cellular wall. In part, it is due to the overexpression of genes codifying for membrane transporters.

The threshold values that allow to differentiate a hyperaccumulating plant from a non-hyperaccumulating one are related to the specific phytotoxicity of each heavy metal. According to this criterion, hyperaccumulating plants are plants that when grown on natural soils accumulate in the aerial parts (in grams of dry weight):

• > 10 mg·g^-1 (1%) of Mn or Zn,
• > 1 mg·g^-1 (0,1%) of As, Co, Cr, Cu, Ni, Pb, Sb, Se or Ti
• or > 0,1 mg·g^-1 (0,01%) of Cd.

Minuartia verna, copper hyperacumulating plant (Autor: Candiru, Flickr, CC).

THE ORIGIN OF HYPERACCULATING PLANTS AND THEIR IMPLICATIONS

Till the moment, several hypothesis has been proposed to explain why certain plants can hyperaccumulate heavy metals:

• Tolerance and presence of metals in soils.
• Resistance to drought.
• Interference with other neighbouring plants.
• Defence against natural enemies.

The most supported hypothesis is “Elemental defence”, which indicates that certain heavy metals could have a defensive role against natural enemies, such as herbivores and pathogens. So, in the case these organisms consume plants, they should present toxic effects, which would lead them to die or at least to reduce the intake of this plant in future. Even though heavy metals can act through their toxicity, this does not guarantee plants will not be damaged or attacked before the natural enemy is affected by them. For this reason, it is still necessary a more effective defence which allow to avoid the attack.

In contrast, according to a more modern hypothesis, the “Joint effects”, heavy metals could act along with other defensive organic components giving rise to a higher global defence. The advantages of inorganic elements, including heavy metals, are that they are not synthetized by plants, they are absorbed directly from the soil and thus a lower energetic cost is invested in defence, and also they cannot be biodegraded. Even though, some natural enemies can even avoid heavy metal effects by performing the chelation, i.e., using chelators (substances capable of binding with heavy metals to reduce their toxicity) or accumulating them in organs where their activity would be reduced. This modern hypothesis would justify the simultaneous presence of several heavy metals and defensive organic components in the same plant, with the aim to get a higher defence able to affect distinct natural enemies, which would be expected to do not be able to tolerate different element toxicity.

Thlaspi caerulescens, zinc hyperaccumulating plant (Autor: Randi Hausken, Flickr, CC).

On the other hand, it has been shown that certain herbivores have the ability to avoid the intake of plants with high levels of heavy metals, doing what is called “taste for metals“. Although this is known to occur, the exact mechanism of this alert and avoidance process is still uncertain.

Solanum nigrum, cadmium hyperaccumulating plant (Autor: John Tann, Flickr, CC).

Additionaly, even tough heavy metal concentration in plant are really high, some herbivores manage to surpass this defense by being tolerant, i.e., their diet allows them to intake high dosis of metals and, thus, consume the plant. This could lead to think some herbivores could become specialist in the intake of hyperaccumulating plants, and, thus, this type of defence would be reduced to organisms with varied diets, which are called generalists. It has been demonstrated to not be true, as generalists herbivores sometimes present a higher preference and tolerance for hyperaccumulating plants than specialist organisms.

For all these reasons, it can be said that evolution is still playing an important role in this wonderful weaponry war.

 REFERENCES

• Boyd, R., Davis, M.A., Wall, M.A. & Balkwill K. (2002). Nickel defends the South African hyperaccumulator Senecio coronatus (Asteraceae) against Helix aspersa (Mollusca: Pulmonidae). Chemoecology 12, p. 91–97.
• Boyd, R. (2007). The defense hypothesis of elemental hyperaccumulation: status, challenges and new directions. Plant soil 293, p. 153-176.
• Boyd, R. (2012). Elemental Defenses of Plants by Metals. Nature Education Knowledge 3 (10), p. 57.
• Laskowski, R. & Hopkin, S.P. (1996). Effect of Zn, Cu, Pb and Cd on Fitness in Snails (Helix aspersa). Ecotoxicology and environmentak safety 34, p. 59-69.
• Marschner, P. (2012). Mineral Nutrition of Higher Plants (3). Chennai: Academic Press.
• Noret, N., Meerts, P., Tolrà, R., Poschenrieder, C., Barceló, J. & Escarre, J. (2005). Palatability of Thlaspi caerulescens for snails: influence of zinc and glucosinolates. New Phytologist 165, p. 763-772.
• Prasad, A.K.V.S.K. & Saradhi P.P. (1994).Effect of zinc on free radicals and proline in Brassica and Cajanus. Phytochemistry 39, p. 45-47.
• Rascio, N. & Navari-Izzo, F. (2011). Heavy metal hyperaccumulating plants: How and why do they do it? And what makes them so interesting?. Plant Science 180 (2),p. 169-181.
• Shiojiri, K., Takabayashi, J., Yano, S. & Takafuji, A. (2000) Herbivore-species-specific interactions between crucifer plants and parasitic wasps (Hymenoptera: Braconidae) that are mediated by infochemicals present in areas damaged by herbivores. Applied Entomology and Zoology 35, p. 519–524.
• Solanki, R. & Dhankhar, R. (2011). Biochemical changes and adaptive strategies of plants under heavy metal stress. Biologia 66 (2), p. 195-204.
• Verbruggen, N., Hermans, C. & Schat, H. (2009). Molecular mechanisms of metal hyperaccumulation in plants. New Phytologist 181 (4), p. 759–776.
• Wenzel, W.W. & Jockwer F. (1999). Accumulation of heavy metals in plants grown on mineralised soils of the Austrian Alps. Environmental pollution 104, p. 145-155.

Islands as natural laboratories for evolution

Islands are natural laboratories where we can study evolution in vivo. Whether from volcanic or continental origin, the fact that islands being isolated from the mainland by the sea makes that island biota present spectacular adaptations, sometimes originating giant or dwarf species in comparison with their mainland relatives. In this article, we describe the evolutionary mechanisms behind this phenomenon and talk about some striking examples.

Islands can have a volcanic origin, involving the emergence of virgin lands that will be colonized involving new adaptations to the new conditions. Islands can also have a continental origin, involving the separation of the mainland by tectonic processes and isolation of fauna and flora before connected.

Volcanic conus aspect in Hawaii. Source: Steve Juverston, via Flickr.

EVOLUTION MECHANISMS ACTING IN ISLANDS

Generation of new species caused by the emergence of a geographic barrier, such as the emergence of a range, changes in sea level or emergence of new islands by tectonic movements is a process known as allopatric speciation and is the main process acting on islands. We can described two kinds of allopatric speciation:

1. Vicariant speciation: when two populations are separated by a geographic barrier, for example when a piece of land separated from the mainland. An example is the island of Madagascar, that when separated from Africa left the biota of the island isolated from the continent by the sea.
2. Peripatric speciation: a new population establishes and gets isolated in a new environment by a very small number of individuals from a larger population. This is the case of the colonization of a sterile land, such as oceanic islands. In this case, the individuals that colonize the new environment may not represent the genetic pool of the original population and with time and reproductive isolation; may originate a new species (founder effect).

The great British naturalist and creator of the theory of evolution, Charles Darwin, insipirated on their findings into the volcanic archipelago of the Galapagos to develop his great theory, paradigm of modern science.

Oceanic islands are formed by exploding volcanoes or movements of the mid-ocean ridge. Due to this volcanic activity, groups of islands are formed, each island having its own history, climate, topography and geology. This creates a perfect scenário to observe how evolution works because each population reaching a new island is affected by different environmental pressures and may never come in contact again with other islands populations, forming unique species, endemic to each island. Many naturalists and scientists have studied the evolution in vivo in volcanic origin archipelagos such as the Hawaiian Islands, Seychelles, Mascarene Islands, Juan Fernandez archipelago or Canary Islands. One of the last islands appeared in the Atlantic Ocean is the Suerty Island, emerged at 1963 30 km southwards of Iceland. Since then, life advent has been studied to understand ecological and evolutionary mechanisms acting in island colonization.

Suerty Island in eruption, in the south of Island. Source: Wikimedia.

ISLANDS ADAPTATIONS: GIGANTISM AND WOODINESS

Often oceanic islands, present no predators and this triggers the appearance of very curious adaptations. One of the most surprising processes is gigantism in animals or woodiness acquisition in plants.

Woodiness acquisition in islands by herbaceous plants on the continent has been documented in several families and islands around the world. The cause of this phenomenon would be the absence of herbivores and competitors in sterile islands, which would allow developing a greater height willing to reach sunlight.

For example, in Hawaii we found the alliance of the Hawaiian silverswords. It comprises 28 species in three genus (Argyroxiphium, Dubautia and Wilkesia), all woody members of the Asteraceae family or sunflowers. Their closest relatives are perennial herbs in North America.

Hawaiian silversword aspect from Argyroxiphium genus (left) and their closest relatives in mainland (right), from Raillardella genus. Source: Wikimedia.

In the Canary Islands, there are many examples of this phenomenon. Echium genus of Boraginaceae or borage and forget-me-not family contains about 60 species, of which 27 are located in different islands of volcanic origin in the Macaronesia (Canary Islands, Madeira and Cape Verde). Almost all members of this genus found in Macaronesia are bushes, forming an inflorescence that can reach up to three meters high, being the symbol of the Teide National Park (called tajinastes) while his nearby relatives are Eurasians herbs such as blueweed (Echium vulgare).

Echium wildpretii (left) in Tenerife and one of its closest relative from mainland (Echium vulgare) on the right. Source: Wikimedia.

Also in the Macaronesia, we find another example in the Euphorbiaceae family. Euphorbia mellifera, endemic to the Canary Islands and Madeira and E. stygiana endemic to Azores are endangered or critically endangered trees according to the IUCN, which can grow up to 15 meters high, being part of the laurisilva vegetation, a subtropical humid forest typical from Macaronesia. Their nearest relatives are Mediterranean herbaceous species.

Euphorbia mellifera in Maderia (left) and one of his closest relatives from the Mediterraneum basin (right, E. palustris). Source: left Laia Barres González and right Wikimedia.

In the animal kingdom, we also find peculiar adaptations. Herbivorous inhabiting islands usually have no predators or competitors, triggering appearance of larger species than in the mainland, where large carnivores avoid this characteristics incompatibles with hiding or escaping.

One of the most famous examples of island gigantism are the Galapagos giant tortoises (Chelonoidis nigra complex), including about 10 different species, many endemic to a single island of the archipelago. This turtles are the most long-lived and largest in the world. They can reach two meters in length and 450 kg in weight and can live more than 100 years.

Galapagos giant tourtle. Source: Wikipedia.

Also among the reptiles, there are the Gallotia giant lizards of the Canary Islands. There are several single island endemic species: G. auaritae in La Palma, believed extinct until the discovery of several individuals in 2007, G. bravoana in La Gomera, G. intermedia in Tenerife, G. simonyi in El Hierro and G. stehlini in Gran Canaria, among others. Among the giant lizards of the Canary Islands there is the extinct Gallotia goliath, reaching up to 1 m length and currently being included in the G. simony circumscription.

Gallotia stehlini in Gran Canaria. Source: El coleccionista de instantes Fotografía & Vídeo via Flickr.

Another example is Flores island in Indonesia, where we found a giant rat (Papagomys armandvillei) doubling the common rat in size. Interestingly, hominid fossils having experiences the contrary process were also found in this island, since it was dwarf primate compared to the Homo sapiens current size. It is Homo floresiensis, who was only 1 meter tall and weighed 25 kg. It became extinct about 50,000 years and coexisted with Homo sapiens.

Giant rat (Papagomys armandvillei) from Flores. Source: Wikimedia.

Dwarfism is another evolutionary process that may occur on islands caused by the lack of resources in some islands, compared to mainland.

Unfortunately, islands holds a peculiar and unique biota that is suffering from of exploitation and extinction. The islands conservation biology helps to understand and preserve this natural heritage so rich and unique.

REFERENCES

Barahona, F.; Evans, S. E.; Mateo, J.A.; García-Márquez, M. & López-Jurado, L.F. 2000. Endemism, gigantism and extinction in island lizards: the genus Gallotia on the Canary Islands. Journal of Zoology 250: 373-388.

Böhle, U.R., Hilger, H.H. & Martin, W.F. 2001. Island colonization and evolution of the insular woody habit in Echium L. (Boraginaceae). Proceedings of the National Academy of Sciences 93: 11740-11745.

Carlquist, S.J. 1974. Island biology. New York: Columbia University Press.

 Foster, J.B. 1964. The evolution of mammals on islands. Nature 202: 234–235.

Whittaker, R.J. & Fernández-Palacios, J.M. 2007. Island biogeography: ecology, evolution, and conservation, 2nd edn. Oxford University Press, Oxford.

Epiphytes, plants that do not need soil

We often hear that epiphytes plants live on the air and it really seems like this, because they don’t nearly need soil to develop. They grow on trunks taking advantage of his height in search of the source of energy much wanted in tropical forests: the sun. In this article we describe epiphytes adaptations and the most common epiphytic groups of these amazing plants.

Epiphytes adaptations

The epiphytes live on other plants without parasitize them or damaging any of its organs or functions. Epiphytes take advantage of other plants structures as physical support to grow into the shaded forest canopy, using the trunks and branches of older trees to reach more height and catch the sunlight. Epiphytes never touch the ground; they are adapted to live on the air!

Epiphytic plants including Cactaceae, Bromeliaceae and ferns growink on a trunk. Source: Barres Fotonatura.

They have amazing adaptations as a result of this habit, such as:

• The ability to capture water and nutrients from the air, the rain and the small amount of soil or organic debris that may remain in the trees trunk where they root.

• Their roots are much more adapted to anchor to the trunks that to absorve water and nutrients.

• Frequently, they develop structures to accumulate moisture.

Although epiphyte plants depend on its host to obtain their nutrients, sometimes they grow so much that overload their host and end up killing their support. This is the case of some Ficus (Moraceae), called “strangler fig” that develop aerial roots around other trees without letting them grow.

Hollow structure left by a stranges fig after killing its hoste. Source: Wikipedia.

Thanks to the epiphytes contribution we can say that tropical rain forest is organized in a vertical gradient along the trees trunks, where we find organism diversity organized according to their distance to the ground. Epiphytes are largely responsible for the extremely rich biodiversity that makes tropical rainforests the most complex ecosystems on Earth. Besides providing different layers of vegetation along height, epiphytes provide shelter and nutrients to different insects and amphibians; who use water stored in the epiphytes leaves as a shelter or nest in the refuge generated in the middle of the trunk.

Water accumulated on a Bromeliad. Source: Otávio Nogueira, Creative Commons.

Epiphytes are found mostly in tropical rainforests, where dozens epiphytes have recorded on a single tree. However, in temperate climates or even deserts we can also found  drought tolerant epiphytic species.

Epiphytes diversity

Currently, approximately 25,000 species are epiphytes. Most common and known epiphytes are Bromeliaceae and Orchidaceae families and ferns. Epiphytism has appeared several times throughout evolution and we found examples in other tropical spermatophytes (plants with seed and trunk) like Ericaceae, Gesneriaceae, Melastomataceae, Moraceae and Piperaceae and also in seedless plants (lichens, mosses and liver) of temperate climates.

Orchids

Orchids have the highest number of epiphytic in the world, with 20 tropical epiphytic genera. The genus with much epiphytes species number are Bulbophyllum (1800) and Dendrobium (1200). The genus of epiphytic orchids Phalaenopsis (60 species) is cultivated worldwide because of its beauty. In fact, many plants used in interior gardening are epiphytes because they have few nutrients and water requirements.

Epidendrum sp. orchids. Source: Barres Fotonatura.

Among orchids, we wanted to highlight a species known for a different reason: the vanilla (Vanilla planifolia), native to Mexico and Central America, where it was consumed with cocoa. It was imported to Reunion island and Madagascar (currently first world producers) by the Spaniards when they discovered their amazing flavor. The vanilla crops imitate their naturally grow on trees, and vanilla plants are not grown on ground, but on logs. The part of the vanilla plant that is consumed is the still immature fruit, after a curing process.

Vanilla cultivation on logs. Source: pixabay.com

Orchids have one of the most complex pollination systems throughout the plant world, with several cases of monospecific coevolution systems linked to insects and hummingbirds. Vanilla is another example, as it is only pollinated by Mexican native bees and hummingbirds, so pollination does not occur naturally in the cultivation areas and it must be done by hand. Normally, women and children still practice this handmade technique pollinating each vanilla flower to get its precious fruit. In fact, vanilla is the world’s most expensive crop, by weight.

Vanilla flower. Source: Wikipedia.com.

Bromeliads

Bromeliaceae includes more than 3,000 neotropical species, most of them epiphytic. The most species rich genera are Tillandsia (450), Pitcairnia (250), Vriesia (200), Aechmea (150) and Puya (150). The leaves of bromeliads grow in rosette facilitating the accumulation of water. The cultivation of bromeliads has been prohibited in Brazil (where we found 43% of Bromeliaceae native species) by ignorance, because it was thought that this water favored the reproduction of Aedes aegypti, mosquito transmitter of Zika, dengue and chikungunya virus. Actually, bromeliads have secondary compounds that prevent the proliferation of this mosquito eggs and larvae while the water inside the leaves creates a micro-habitat that accumulates nutrients that feed other insects, amphibians and native birds that can help fighting it. Bromeliaceae flowers have bright colors and are accompanied by showy bracts also attracting the attention of pollinators, especially hummingbirds and bats. Many bromeliads are  used as ornamental plants, especially Tillandsia and Guzmania.

Tillandsia sp. Source: Barres Fotonatura.

Epiphytes from temperate climates

One of the most incredible epiphytic ferns is the staghorn fern (Platycerium bifurcatum), widely used as an ornamental plant. The staghorn fern is native to Australia but is found in all tropical areas used for gardening. This fern develops two leaf shapes: the first kind is kidney-shaped and does not produce spores; its function is to anchor to the trunk. These leaves eventually acquire a brown coloration and form a base from which the second kind of leaves grow; which are fertile and therefore produce spores. The fertile leaves are long and bifurcated and can grow up to 90 cm long. The spores of this fern are produced at the leaves apex that gain a velvet appearance.

The two kinds of leaves in Platycerium bifurcatum. Source: Barres Fotonatura.

At temperate forests, the most common epiphytes are lichens. Among lichens, we want to highlight Usnea or old’s men beard. It is a cosmopolitan genus growing on conifers and deciduous trees. This grayish fruticose lichen grow as curtain shape hanging from trees. Curiously, there is a species of epiphytic bromeliads that reminds Usnea because they share this particular growth form. Its called Spanish moss (Tillandsia usneoides) but is neither a moss or lichen, but a bromeliad with very small leaves growing chained to the ground. Nor is Spanish but lives in America.

Usnea lichen growing as a curtain on temperate climates (left) and Tillandsia usneoides of tropical climates (right): Source: Barres Fotonatura and Wikipedia.com.

The epiphytes are still little known because climbing techniques in tropical rainforest have only been developed recently so we still known a little about compared with carnivorous or parasitic plants. Many are still to discover!

REFERENCES

Benzing, D.H. 1990. Vascular Epiphytes: General Biology and Related Biota. Cambridge: Cambridge University Press.

Smith N., Mori S. A., Henderson, A., Stevenson D. W. & Heald, S. V. 2004. Flowering Plants of the Neotropics. New Jersey, USA: The New York Botanical Garden, Princeton university press.

http://www.kew.org/science-conservation/plants-fungi/vanilla-planifolia-vanilla

https://www.anbg.gov.au/gnp/interns-2004/platycerium-bifurcatum.html

The elderly organisms of the oceans

Have you ever wondered which are the longest-lived organisms of the seas and oceans of the Earth? The sea turtles are well known to have long lives. But, ¿which is the oldest organism of the ocean (and the planet)?

BOWHEAD WHALES

The bowhead whales (Balaena mysticetus), also called Arctic right whales, live most of the year associated with sea ice in the Arctic ocean. These marine mammals are among the largest animals on Earth, weighing up to 75-100 tons and with a length of 14-17 m on males and 16-18 m on females.

Bowhead whale (Balaena mysticetus) (Picture: WWF).

More than 20 years ago, in 1993, it was discovered by chance that bowhead whales have a longer life than previously thought. Their lifespan was considered to be about 50 years, but the unexpected discovery let to know that they live more than 100 years. In fact, some individuals are known to have lived for about 200 years.

Which was that fortuitous discovery? An Alaskan Eskimo hunted an individual with the tip of a harpoon inside its blubber. This harpoon was created with a technique not used for 100 years.

They are among the mammals that get much older, even among other whales. And the explanation to this fact lies on the extreme cold of their habitat: they have to invest so much energy in maintaining the body temperature that their first pregnancy is usually at 26 years and, therefore, they have a long life expectancy.

SEA TURTLES

In the famous Disney movie Finding Nemo, Marlin, Nemo’s father, meets Crush, a 150-year-old sea turtle. However, do sea turtles live so much?

Do you want to discover the amazing life of the sea turtles? Do you want to know the reason why sea turtles are threatened?

Sea turtles have long lives, but their age is unknown (Picture: Key West Aquarium).

It is well-known that sea turtles have a long life, but their ages are barely known. It has been confirmed that growth lines in some turtle bones are laid down annually, but due to growing at different rates depending on the age, this cannot be used to estimate their age.

However, scientist believe that these awesome reptiles may live long like whales. Those turtles that outlive the first stages of life can expect to live at least 50 years. In addition, biological aging is nearly suspended for these animals.

Despite unknowing the age of the oldest wild sea turtle, it is said to be a 400-year-old captive sea turtle in China.

THE OLDEST KNOWN ANIMALS

Black corals are the oldest known animals on Earth. Notwithstanding, they are not the oldest organisms on the planet.

Leiopathes sp. is a genus of black corals that can live several millenniums (Picture: CBS News).

These coal-dark-skeleton corals grow a great deal less than a millimetre per year, such as the Mediterranean red coral. Despite its name, they usually show yellow, red, brown and green colours. Although they are considered deep-sea corals, they are found worldwide and at all depths.

Research in 2009 demonstrated that a Hawaiian black coral individual included in the Leiopathes glaberrima species had been living and growing since the building of Egyptian pyramids; 4,600 years ago.

Like sea turtles, in case an individual survives the first century of age, there is every likelihood of  living for a millennium or more.

THE IMMORTAL JELLYFISH

It is a fact of life that all living beings die; except for Turritopsis nutricula, the immortal jellyfish. This small (4.5 mm) bell-shaped jellyfish is immortal owing to the fact that possess the capability to age in reverse.

The immortal jellyfish, Turritopsis nutricula (Picture: Bored Panda).

This species starts its life being a mass of polyps growing in the seafloor, which in some point produce jellyfishes that develop gonads to create the following generation of polyps, and then die. This has nothing special in comparison with other jellyfishes. Learn more about these beautiful animals here.

This cnidarian species, under the presence of a stressor or injury, transforms all its cells into larval forms. It is that changes from an adult to a larva. Then, every single larva can transform into a new adult. That process is named transdifferentiation. Little do scientists know about this process in the wild.

Transdifferentiation in Turritopsis nutricula (Picture: Bored Panda).

THE OLDEST ORGANISM ON EARTH

The oldest organism on Earth is neither an animal, algae nor a microorganism. The most elderly organism in the planet is a plant. In concrete, a marine plant known as Posidonia oceanica, commonly known as Neptune Grass or Mediterranean tapeweed. Do you want to know the reason why the Posidonia ecosystems are considered the marine jungles?

Posidonia oceanica meadow (Picture: SINC).

Spanish researchers found out that in Formentera (Balearic Islands) there is a 100,000-year-old Posidonia clone. This means this is the longest-living organism on the biosphere.

The key to understand its age is the clonal growth: it is based on the constant division of cells placed in the meristems and on the extremely slow growth of its stalk (rhizomes).

REFERENCES

• Arnaud-Haond S, Duarte CM, Diaz-Almela E, Marba` N, Sintes T, et al. (2012) Implications of Extreme Life Span in Clonal Organisms: Millenary Clones in Meadows of the Threatened Seagrass Posidonia oceanica. PLoS ONE 7(2): e30454. doi:10.1371/journal.pone.0030454
• NOAA: Black corals of Hawaii
• Palumbi, S.R & Palumbi, A.R (2014). The extreme life of the sea. Princepton University Press
• Reference: The oldest sea turtle
• Rugh, D.J. & Shelden, K.E.W. (2009). Bowhead whale. Balaena mysticetus. In Perrin, W.F; Würsig, B & Thewissen, J.G.M. Encyclopedia of Marine Mammals. Academic Press (2 ed).
• Schiffman, J & Breen, M (2008). Comparative oncology: what dogs and other species can teach us about humans with cancer. The Royal Society Publishing. DOI: 10.1098/rstb.2014.0231
• WWF: How long do sea turtles live? And other sea turtle facts
• Cover picture: Takashi Murai (Bored Panda)

The great journey of coconut

Cocos nucifera L., the coconut tree, is one of the most emblematic palm trees from tropical countries: photographed by tourists on bucolic beaches; basis element for the gastronomy and culture in many countries and a source of inspiration to many artists, is still a mystery for scientists. Where is coconut from originally? The answer to this question is now a little more clear thanks to a phylogeographic study, discipline that integrates population genetics with biogeography. In this post, we reveal this and other questions about this iconic palm.

COCONUT TREE CHARACTERISTICS

Coconut tree belongs to Arecaceae, the family of monocots with tree aspect, known as palm trees. Yes, you read right! All palm trees are closer to grasses (cereals) than to deciduous trees. In fact, its trunk is not a real one because it has no tissues allowing them to growth in diameter and therefore not branches. If you look closely to any palm tree trunk, you’ll see that it always has the same thickness, it only grows vertically. It’s the stipe and it is formed by the superposition of the leaves base and the scarfs we see on the trunk are the marks left by the falling leaves petioles. If you ever see a cut stipe, you’ll see that it doesn’t have the typical structure in growth rings but fiber mass. In fact, this structure is optimal to survive to tropical winds because it is both tough and flexible, providing flexibility necessary not to break while tropical winds and also stand firm.

Palm tree stipe (Source: Public Domain Pictures).

The function of the stipe is to support the weight of the leaves, flowers and fruits; that grow on top. The Arecaceae leaves are pinnate. The flowers grows in racemous inflorescences and fruits usually are drupe type, such as date or coconut.

In the Mediterranean region we only have two species of native palms. Mediterranean dwarf palm (Chamaerops humilis) has its northern limit at the Garraf coast. The Cretan palm (Phoenix theophrastii) is endemic to southern Greece, Turkey and Crete.

Mediterranean dwarf palm (Chamaerops humilis) at Catalonian coast (Source: Wikimedia).

COCONUT TREE USES

Arecaceae contains approximately 2600 species classified in about 202 genera. The coconut palm is monotypic because it is the only species in the Cocos genus. It is found in 89 tropical countries and is considered the tree of life because it provides resources such as:

– Food: Coconut is a highly nutritious fruit, rich in fat (is the most caloric fruit consumed by humans), micronutrients (it is very rich in potassium) and fiber. From dried endosperm (the white “meat” or copra, which is actually the seed) we can also extract milk and coconut oil, widely used for cooking, cosmetics and even as biofuel. The sweet sap of the inflorescence is also consumed as wine after its alcoholic fermentation.

Dried coconut to elaborate copra (Source: Peter Davis / AusAID).

–     Water : green coconut contains drinking water rich in micronutrients. It is consumed in many tropical countries as an isotonic drink.

– Construction Material: mesocarp fiber is widely used to make ropes, mats, planting substrate, etc. Endocarp, the layer that covers the meat is used as a container for food and drink, decoration or as a musical instrument. The leaves are also used to produce handicraft (rugs, toys, baskets, etc.), to cover roofs and as carbon. The wood has traditionally been used for houses construction.

– Religious Element: Coconut is part of different spiritual manifestations in Hinduism and some Philippines communities.

Coconut inner parts schema.

OCEANIC DISPERSAL

Coconut is adapted to hydrochory, ie dispersal by water. Coconut is one of the little fruits known to have been adapted to oceanic dispersal. The water contained by the coconut enables its floatation and facilitates its dispersal over long distances. In addition, the fruit is resistant to salinity and does not rot. When it gets the beaches, it can germinate after having sailed 110 days (or 4000 km). However, its pantropical distribution is not only due to its oceanic dispersal but is also linked to its cultivation by humans. Human migration to Southeast Asia would not have been possible without the coconut cultivation and coconut should not have been so widely dispersed if not for its value.

It is therefore quite likely that the wide variety of coconut uses has conditioned its migration history. There are several hypotheses about coconut origin. De Candolle, at 1886, proposed that the coconut was American, based on the distribution of all other members of the Cocoseae tribe (200 species distributed in 20 genera from America), except for the African palm oil (Elaeis guineensis, the source of  palm oil). Other hypotheses (Beccari, 1963) claim of an Asian origin because morphological variation in the region is greater, popular names and uses are more diverse on this continent and in addition there is an Asian endemic hermit crab (Brigues latro) that can only live in symbiosis with coconut. So from Asia and with human help, coconut palm tree would have migrated eastwards to the Pacific ocean and westwards to the Indian Ocean.

Coconut tree distribution (Source: Gunn et al., 2011).

COCONUT TREE ORIGIN

Recent studies using DNA as a source of information have made new discoveries about coconut origin. It seems that despite the wide variety of cultivars and human manipulation, coconut palm tree populations have a strong structure into two genetic groups, one in the Indian Ocean (including Indian and African populations), and the other in the Pacific ocean (including Southeast Asian, Caribbean and South American populations). Thus, all current coconut populations come from one of these two groups, demonstrating its Asian origin. For example, Brazilian and Caribbean populations come from the Indian group and the American Pacific coast populations come from Southeast Asia.

Coconut tree genetic groups discovered by Gunn et al. (2011).

Therefore, it seems that the coconut tree is native to both Pacific and Indian coasts and that coconut cultivation arose independently in these two regions.

REFERENCES

• Beccari, O. 1963. The origin and dispersal of Cocos nucifera. Principes 7: 57–69.
• de Candolle, A. 1886. Origin of cultivated plants. New York: Hafner. 468 p.
• Cook, O.F. 1911. History of the Coconut Palm in America. American Journal of Sciences 31(183): 221-226.
• Gunn, B.F. 2004. The phylogeny of the Cocoeae (Arecaceae) with emphasis on Cocos nucifera. Annals of the Missouri Botanical Garden 91: 505–522.
• Gunn, B.F., Baudouin, L. & Olsen, K. M. 2011. Independent Origins of Cultivated Coconut (Cocos nucifera L.) in the Old World Tropics. PLoS ONE 6(6): e21143.
• Meerow, A.W., Noblick, L., Salas-Leiva, Dayana E., Sanchez, V., Francisco-Ortega, J., Jestrow, B. & Nakamura, K. 2015. Phylogeny and historical biogeography of the cocosoid palms (Arecaceae, Arecoideae, Cocoseae) inferred from sequences of six WRKY gene family loci. Cladistics 31: 1096-0031.
• Scientific American: Coconuts: not indigenous, but quite at home nevertheless

The marine jungles: the meadowlands of Posidonia

Posidonia and other seagrasses are one of the most important marine ecosystems on Earth. Many dare to categorize them as the jungles of the sea, for its high biodiversity. It is what we are going to see in this article, especially focusing on the Posidonia oceanica‘s meadows!

WHAT ARE MARINE PHANEROGAMS?

The seagrasses are plants that colonized coastal marine environments, being present in all oceans and seas, except the Antarctic. There are about 66 species.

All have a similar pattern: a horizontal underground rhizome (a thick buried stalk), from which are born the roots and vertical ramifications from where emerge leaves.

Throughout evolution, they have acquired the necessary adaptations to live in an environment with a high concentration of salts. They have the ability to perform underwater pollination by little flowers, in addition to reproduce asexually.

As we have already mentioned, we will focus on Posidonia oceanica, an endemic species of the Mediterranean Sea. It has the typical structure mentioned above, but among its peculiarities there are leaves of 0.5 cm wide and one meter long, grouped in bundles of 4-8 leaves.

Posidonia oceanica’s meadow (Picture: Manu Sanfélix).

In just one square meter can be 10,000 leaves. As a result, the particles that fall to the bottom are trapped and form what is known as “matte”, a very compacted substrate that rises slowly (10-18 cm/century), which acts as a barrier against the waves, favouring the formation of beaches. Do you want to know why we are losing beaches?

Did you know that on the island of Formentera (Balearic Islands, Spain) there have been found an individual of Posidonia older than 100,000 years?

BIODIVERSITY IN POSIDONIA MEADOWS

Posidonia meadows and other seagrasses are ecosystems with high biodiversity. In addition to the organisms living permanently, others reproduce, put the lay or refuge there. There have been described about 1,000 species in them.

Despite the high associated biodiversity, only few species are able to feed on the plant. Examples include salema progies (Sarpa salpa), the green turtle (Chelonia mydas), some sea urchins such as Paracentrotus lividus … all with symbiotic bacteria in the digestive tract.

Salema porgy (Sarpa Salpa) (Picture: Jordi Regàs, CIB)

There are many algae and animals that live attached to the leaves or rhizomes, called epiphytes. Examples include the hidrozoa Aglaophenia harpago and the bryozoan Lichenopora radiata. But undoubtedly the most characteristic epiphyte animal on Posidonia is Electra posidoniae. This bryozoan form a narrow structure above the plant’s leaves.

Hidrozoa Aglaophenia harpago above Posidonia oceanica (Picture: Peter Jonas).

Briozoa Lichenopora radiata (Picture: Javier Murcia).

Briozoa Electra posidoniae (Picture: Jordi Regàs, CIB).

Logically, there are also animals moving on the leaves. These are small animals that feed on epiphytes, such as crustaceans, gastropods (snails and slugs); polychaete, flatworms, nematodes and echinoderms. Examples are the nudibranch Diaphorodoris papillata and the crustacean Idotea hectica.

Nudibranch Diaphorodoris papillata (Picture: CIB).

Crustacean Idotea hectica (Picture: David Luquet).

One of the most characteristic animals of the Posidonia oceanica is the nobel pen shell (Pinna nobilis), the biggest Mediterranean mollusc, which can grow to a meter and lives with part of the body buried in sand.

Nobel pen shell (Pinna nobilis) (Picture: Maite Vázquez)

Among the echinoderms, it is considered that the starfish Asterina pancerii is the only strictly linked to the meadow, although sea urchins such as Paracentrotus lividus can become very abundant.

Starfish Asterina pancerii (Picture: Jordi Regàs, CIB).

Sea urchin Paracentrotus lividus (Picture: Jordi Regàs, CIB).

Other animals that roam freely in the meadow are fishes. The painted comber (Serranus scriba) is the most common; but the most unique is Opeatogenys gracilis, green in order to camouflage itself in the leaves. Other that camouflage really good are the fishes from the genus Syngnathus, such as S. typhle and S. acus.

Painted comber (Serranus scriba) (Picture: Jordi Regàs, CIB).

Opeatogenys gracilis (Picture: Manuel Campillo).

Syngnathus typhle (Picture: Sea Horse Project).

POSIDONIA HAS A HIGH ECOLOGICAL IMPORTANCE

As we have seen, Posidonia meadows are areas with high biodiversity of animal and plant species. So, it is home to many species at different stages of their life cycle.

But its importance goes further. Due to its growth through underground rhizomes, Posidonia retains the sand and, century after century, forms a natural barrier that provides protection for the coast, allowing the formation and gives stability to beaches, dunes and coastal forests.

Finally, a lot of organic matter is dispersed by currents and waves to other ecosystems.

REFERENCES

• Ballesteros, E & Llobet, T (2015). Fauna i flora de la mar Mediterrpania. Ed. Brau
• Departament de Medi Ambient, Generalitat de Catalunya (2002). Biodiversidad y medio marino.  Mediterrània viva. Editorial Anthias SL.
• Minguell, J (2008). Flora i fauna del Mediterrani.
• Ruiz, JM; Guillén, JE; Ramos Segura, A & Otero MM (Eds) (2015). Altas de las praderas marinas de España. IEO/IEL/UICN. Murcia-Alicante-Málaga. 681 pp.
• Triptych: Las praderas de Posidonia en peligro. Parc Natural del Montgrí, les Illes Medes i el Baix Ter.
• Cover picture: G. Pergent (INPN).