guia do novo coronavirus
Imprimir Republish

Botany

Textures of the forest

Genetic classification solves the evolutionary mystery of vines and could provide guidance for the preservation of tropical rainforests.

eduardo cesarFlying seeds: in the shape of a disc, common in the Cerrado, and elongated (at the side) typical of humid forestseduardo cesar

Lúcia Garcez Lohmann discovered very early the pleasure of organizing the world around her. At five years of age she began an ordered collection of stamps showing plants and flowers and at 16 years she had no doubt about what profession she would follow: she would study biology in order to study systematics, the classification of living beings. She began studying a family of microscopic fungi that consume the scales of fish and reptiles. But she became enchanted with a family of plants with flowers in the form of a bell and of intense color that ranges from blood red to brilliant white: the bignonia, with around 850 species of varied forms and sizes that distribute themselves throughout the tropical regions of the planet.

Lúcia has traveled the world studying this family of plants to which the Golden Trumpet Tree (ipê-amarelo), Brazil’s tree symbol, belongs, and is now proposing a more trustworthy classification for them. She visited collections in the United States and Europe and penetrated into the forests of Latin America in order to get to know close up where they were and what bignonia look She specialized in a group of almost 400 species of this family that for decades whetted the appetite of botanists for three reasons. The first is that this group brings together the largest variety in the Americas of vines or lianas, creepers with imitation wooden tails that grow spiraling up the tree trunks, spreading up into the crowns in search of light, necessary for their survival.

The other reason is that several of these plants, which thread impenetrable networks in the interior of forests and connect the crown of the trees to the ground, serving as bridges for monkeys and sloths, have medicinal potential. Some Latin America populations use them to work against diarrhea, malaria, hepatitis, Leishmaniosis and cancer. In some countries, they serve as a condiment as they have the aroma and taste of garlic or carnation, as well as being useful for the construction of furniture and houses. But professor Lúcia felt a special attraction for these plants because they had formed a group with an intricate evolutionary history whose relationships of kinship challenged botanists for almost two centuries.

Beyond appearance
Better to say, had challenged. In an article published during 2006 in the American Journal of Botany, botanist Lúcia presented the genealogical trees that unraveled the evolutionary history of this group. Now, in a 400 page article, to be published in the Annals of the Missouri Botanical Garden, she is presenting a new classification that reorganizes this group of bignonia based on criteria that go beyond any similarities in their flowers and fruit, as was the case up until recently, and promises to unravel the knots of this lianas tangled forest. Starting from the genetic material of these plants, she redistributed the 400 species into 22 genres. The largest, Adenocalymma, is made up of 78 species of vines and shrubs from the tropical regions of the Americas. With the new classification, some genres, such as the Fridericia, have gone on to include a greater number of species – before there was one, today there are 69. Only the genres Callichlamys and Manaosella continue, each one, with a single species: the Callichlamys latifolia, a creeper with yellow flowers, found in Brazil and Mexico; and the Manaosella cordifolia, described in Manaus.

This is a major leap forward in relation to the previous classification in which there had been 47 genres, 30 of them with up to three species. For anybody who works with classification, a system with a lot of genres grouping together few species is not very helpful: it hardly provides any information about the degree of kinship, impeding making forecasts about species included in each genre. Without this type of information, little can be discovered about when and where the plants sprung up or how and why they made themselves highly successful and if they disseminated themselves in all of the tropical regions of the Americas, originating species as distant as the creeper named Caatinga Neojobertia brasiliensis, with yellow flowers, or the Adenocalymma cladotrichum, a creeper with a thick stalk that produces fruit in the form of a string bean some half meter in length.

In the article published in the Annals of the Missouri Botanical Garden, 180 species received a new name because they changed genres. There is, as well, a detailed illustration of each genre and maps with the geographical distribution of 400 species. “I hope it’ll no longer be necessary to redo this classification and, starting from now, we can manage to really advance in the investigation about origin, evolution and diversification of this plant group,  the richest in varieties of the vines”, commented the botanist and  professor from the University of Sao Paulo, as well as a researcher at the Botanic Garden of Missouri, United States, where she has been working on the collection of another student of these plants, the botanist Alwyn Gentry, who died in 1993.

From the time that the English botanist David Don proposed the first classification of this group of bignonia in 1838, some 170 years have passed with people running round in circles. “Each person who set out to study them created a new classification system, based on subjective criteria, and the situation didn’t move forward”, explained professor Lúcia, who at 33 years of age is turning herself into an international reference on the question. The new classification promises to be long lasting because it comes from a more adequate tool, only recently available: molecular methodology. This method allows for organizing plants by the degree of their kinship based on genetic characteristics, and no longer only on the comparison of their forms of flowers, fruit and seeds.

“For example, this new classification will allow for a much better guided search for compounds with pharmacological potential”, affirmed professor Lúcia. She evaluated the proximity between the group’s species by comparing the mutations of two genes: the ndhF, associated with the storage of solar energy in the form of sugars, and the PepC, linked to the breakdown of these sugars and the liberation of energy. These genes perform an essential role in survival and allow for kinship evaluation between the species on a timescale of up to millions of years ? they have been identified in close evolutionary species and present differences as the kinship diminishes. “These genes are found in distinct regions of the genome, and, even at that, relate coincidental history”, advised professor Lúcia. “For this reason it’s highly probable that the new genealogical tree truly represents the kinship between these plants.”

FABIO COLOMBINICascading: the creepers search for light at the top of treesFABIO COLOMBINI

First answers
During the 13 years in which she traveled through the Brazilian forests and the others of six Latin America countries (Costa Rica, Suriname, French Guiana, Peru, Bolivia and Panama), professor Lúcia walked for days, crossed rivers, and when necessary, climbed 40 meter high trees in her search for her lianas. She collected samples from almost 1,000 examples, today stored in the herbariums of USP and the National Research Institute of Amazonia ass well as the Botanic Gardens of Rio de Janeiro, New York and Missouri. In a pains taking study, she marked out the collection point of each collection using GPS apparatus and her data was added to that of other collections, generating maps with the distribution of the species. Superimposed, these maps reveal an important piece of data for the conservation of these plants: not always is it the natural vegetation areas that need to be preserved in order to house rare species, of major genetic diversity or of evolutionary importance that are legally protected.

On crossing her data with that of fossils, professor Lúcia has managed to reconstruct the group?s evolutionary history. Now one can say when and where these vines sprung from: it was in Brazil in the region today occupied by the Atlantic Rainforest, some 40 million years ago – when the continents had their current form and the mammals had begun to spread themselves throughout the Earth. But this was not the only time. Plants with vine characteristics appeared at three other moments among the bignonia, in the Andes, in Africa and in Asia. But only the group of the Atlantic Rainforest was highly successful and diversified themselves so much, generating the 400 known species.

The findings have also proven that the ancient method of classification, based upon the colors of flowers or shape of fruit, was in fact wrong. Creepers or shrubs with yellow flowers sprung up at six different moments in this group, in genres with no kinship. “This piece of data confirms that the exclusive use of morphological criteria could lead to a classification system that’s not trustworthy”, stated professor Lúcia. Another doubt that was unmasked is that of which came first: the vines, today in the more abundant form, or the shrubs, currently rare? According to professor Lúcia, the first species of this group developed as vines in humid forests. Possibly they were highly successful in these environments with little light because they developed a stock with peculiar anatomy, more flexible and tendrils, filaments that twist themselves around other trees and allow them to reach the highest parts of the forest. Only between 5 and 10 million years afterwards did these vines also spread to regions with a drier and hotter climate such as the current Cerrado when the shrubs emerged.

But the anatomy of the stock and the tendrils does not explain how these plants diversified themselves so much and dominated the tropical regions of the globe. Part of the answer is linked to the form of their seeds. The commonest species in the forests produce seeds with a fine membrane that extends itself to the opposite sides, like open wings. For professor Lúcia, this format favors dispersion in humid environments. When the fruit dries up and opens, they fall from a height spiraling like the helix of a helicopter. However, in the savannahs rounded are more common similar to flying saucers, apparently better equipped for dispersion in dry areas. “When the wind blows, these seeds must fly as if they were Frisbees, the plastic discs that people play with on the beach”, she explained.

As this bignonia group is highly diverse and abundant in tropical forests, it is believed that this serves as a model for understanding what must have occurred with the 300,000 plant species with flowers (angiosperms). Bringing together information about distribution, the form and ecology of these 400 species as to climate, soil and temperature data, professor Lúcia is now attempting to forecast what will happen to their distribution in the case where the planet’s temperature increases a few degrees. As yet she does not have an answer, but she risks a guess: it is highly probable that the forests that today house the major diversity of the world’s plants transform themselves into immense vine tangled areas, since these bignonia grow faster than some trees and are the first to occupy deforested regions.

Republish