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Botany

The smell of the species

The only way of differentiating minuscule orchids from mountainous regions is their pollinating insect, specific to each flower's smell

The orchids with which the biologist Eduardo Borba works have little to do with the large and perfumed flowers common in Brazil and universally admired: the flowers of the species that he studies are rarely larger than two centimeters in width and smell like rotten cheese, rotten fish and even somewhat similar to dog feces.

But it was with them, during his doctorate studies at the State University of Campinas (Unicamp), supervised by João Semir, that Borba discovered something important for the classification of plants, especially those of mountainous regions: distinct species but morphologically identical, were only differentiated by the pollinating insect, attracted through the smell of the flowers – and that there are insects specific to each smell.

Borba announced in March 2000, in the magazine Lindleyana , the conclusion that the pollinating insects are guided by smells, not by the shape of the plants. The finding also served for him to discover a species of orchid, the Pleurothallis fabiobarrosii – a name given in homage to the researcher Fábio de Barros – and a subspecies, Pleurothallis ochreata subsp. cylindrifolia. Later in July of 2001, his study on the processes of pollination made the cover of the magazine Annals of Botany .

“It this really an orchid?” This was the question that Borba heard most often when he showed the objective of his study. Nevertheless, with timid yellow and purple flowers, and long and cylindrical leaves, the orchids pollinated by flies correspond to around 15% of the total of 20,000 catalogued species and to almost all of the thousand species of a gender always left aside by researchers, the Pleurothallis .

“The disinterest is due to the type of pollination, which many consider to be primitive, or to pure prejudice, since these plants don’t have a nice smell or a nice look”, comments Borba, hired in May of last year by the State University of Feira de Santana (Uefs), in the state of Bahia. In fact, the uncommon odors exhaled by the Pleurothallis attract insects of distinct families: flies of the family Phoridae, for example, only pollinate flowers with the smell of rotten cheese while those of the familyChloropidae appreciate species that give off the smell of rotten fish.

Seated and immobile
The researcher concentrated on five species of Pleurothallis pollinated by flies and found in stony lands in the states of Minas Gerais, Bahia, Pernambuco and Rio de Janeiro. Borba made an ambitious plan – to study reproduction, biological flowering, genetic, chemical and morphological variability and the constancy of the pollinating insects – and spent in the field the equivalent of 660 hours in discomfort: he would spend the entire day seated, practically motionless, to observe the comings and goings of the flies on the small orchids.

“Insects are inoffensive and allow for observation with the naked eye at a distance of only one meter”, he tells. Observation in the habitat itself gave him a reasonable sample of the variation within the twenty four populations of the sixteen field locations that he covered: “As the morphology of these plants is very similar, when the material is analyzed alive, in situ, it is very easy to perceive the small differences between the species, contrary to the dry material available in herbariums”.

Diversity
The orchid family is one of the most numerous groups of angiosperms, that is plants with flowers and seeds: around 850 genders and 35,000 species have been catalogued. Brazil has 10% of these species, in a large part endemic – native and exclusively from here. Their size varies from the minuscule Pleurothallis up to flowers of thirty centimeters. They can be found in distinct habitats: ground soil, flooded areas (paludicolous plants), rocky soil (rupicolous) and the trunks of trees (epiphytes). The rupestrian countryside is an ecosystem that lies above 800 meters of altitude, typical of mountain ridge chains.

It is characterized by undergrowth vegetation and herbal grasses in sandy-stony soils or shrubs and herbs in rocky outcrops. Due to the discontinuity of the mountainous formations, many rupestrian species distribute themselves in isolated populations. It is believed that this accounts for the accentuated vegetal diversity and the high degree of endemism of this habitat. Given the environment where they live, over rocks that don’t retain moisture, the Pleurothallis have managed to adapt themselves to accumulating water reserves in their thick stalks and leaves.

The high genetic differentiation of the rupicolous populations – in contrast to their much lesser morphological differentiation – was found principally in the Grão-Mogol and Cabral ridges, regions of great endemism in the north of Minas, as well as other in other ridges of the Espinhaço range. These findings already pointed to the discovery of new species.

The Pleurothallis fabiobarrosii was first found in Grão-Mogol, along with populations ofP. ochreata. At firstl, through the resemblance in the flowers, it seemed that they were dealing with a hybrid of P. ochreata with P. johannensis. Genetic analysis dissipated the doubt and defined a new species. Afterwards the subspeciesP. ochreata subsp.cylindrifolia – also found in Grão-Mogol – was identified through a small differences in the leaves, since the flowers are identical. The new subspecies has thinner and more cylindrical leaves than the common P. ochreata, which only occurs in the northeast of the country, and also has a difference in the chemical composition of its alkaloids.

Borba added to his field work three years of laboratory analysis, in collaboration with researchers from Unicamp and the Royal Botanic Gardens in England. The results came in an unusual manner: they can be measured by their final highlight, the chapters of the thesis were published in international periodicals such as the American Journal of Botany, Annals of Botany, Lindleyana and Biochemical, Systematics and Ecology.

The project
Systematic Bio Studies in species of Brazilian Orchids Orchidaceae Miiófilas (nº 97/08795-8); Modality Assistant research project; Coordinator João Semir – Biology Institute of Unicamp; Investment
R$ 18,832.80 and US$ 12,000

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