Flowering Plants of the Brazilian Semi-arid

Luciano Paganucci de Queiroz

The flowering plants (or angiosperms) are the most diverse group of organisms after the arthropods. They are extremely important for land life, being the main producers of organic matter. Because of the predominance of different life forms, they define the landscapes that nowadays cover most of the planet. Angiosperms also represent the main source of resources for human populations, including the ones that inhabit the Brazilian semi-arid region, providing food, medical products, construction material, fuel and forage.

The Northeast Brazil is usually said to have low floristic diversity. This results from the strong impression made by the overlooking the caatinga (Introduction) – predominant kind of vegetation in the region – in mid dry season, when vegetation is composed by trees and tiny shrubs with no leaves, giving a stark impression of dead vegetation. However, the Northeast region holds more types of vegetation than any other region in Brazil. We can find the Atlantic Rainforest, seasonal forests and inland mountain forests, restinga and shore dunes, mangroves, cerrados (savannah-like vegetation) and ‘campos rupestres’ (Chapter 9), not to mention the caatinga itself. Besides that, recent works have shown that caatinga are highly diverse.

In the Brazilian Semi-arid, the principal vegetation types are the caatingas, seasonal forests, campos rupestres and cerrado, and they can be characterized according to their flowering plant composition. The flora of the cerrados and the seasonal forests represent an extension of that of the Central and SE Brazil , respectively. However, the floras of caatinga and campos rupestres present many autochthone elements and will be more detailed further in this chapter.

» Flowering plant families and their specialists at the main herbaria in the Northeast Brazil

Caatinga

Caatinga occupies most of the 900 thousand km² in the Northeast Semi-arid. It is characterized by a relatively low tree stratum (generally up to 5 m high) without a continuous canopy, trees and shrubs usually with thin stems, frequently thorny, with small or composite leaves, deciduous in the dry season. Cactus and terrestrial bromeliads are also important elements of the caatinga landscape. The herbaceous stratum is short-lived and mainly constituted by therophytes and geophytes that occur only in the short rainy season.

Some authors have considered the caatinga as having a small number of species, poor in endemism at generic and specific levels and not presenting an autochthonous flora, but derived from the floras of the Chaco and of the Atlantic Forest . However, recent systematic studies have shown a very different situation . Around 1,012 species of angiosperms were registered for the Caatinga Biome , 318 species (around 31%) of which were considered endemic, besides 18 genera referred to as endemic to the caatinga (see the updated list of genera). The distribution of this floristic diversity was the main aspect responsible for the recognition of ecoregions in the Caatinga Biome .

Some families present great diversity in the caatinga. Leguminosae is the most diverse, with 293 species in 77 genera, 144 of which are endemic of the caatinga . Species of many genera of Leguminosae contribute for the formation of the tree and shrub stratum that shapes the caatinga landscape, such as Mimosa, Acacia, Caesalpinia and Senna. Other floristically important family is the Euphorbiaceae, with a great diversity of species of the genera Croton (‘velames’), Cnidoscolus (‘cansansões’ or ‘favelas’) and Jatropha (‘pinhões’). Cactaceae also constitutes an important element of the landscape, with their succulent, aphyllous and thorny stems. Fifty-eight species have been registered for the caatinga, 42 endemic to the biome . Typical genera are Cereus (‘mandacarus’), Pilosocereus (‘facheiros’), Melocactus (‘cabeças-de-frade’) and Tacinga (‘palmas’), this last one endemic to the caatinga. The family Bignoniaceae is also well represented, especially with liana species of the genera Arrabidaea, Adenocalymma and Piriadacus, the last one endemic to the caatinga.

Taxonomy of many groups of caatinga is still incipient. Only recently, systematic efforts have been done to teaching taxonomy in the NE Brazil, which has improved the knowledge of the flora and increased the description of new species in different families. Yet, there are few inventories along the region and this gap is worse if we have in mind that the caatinga is highly heterogeneous, with some centers of floristic endemism different from which is considered typical caatinga, like the regions of Raso da Catarina, Dunes of the Rio São Francisco and the Ibiapaba moutain range . Preliminary inventories made in these areas have shown new taxa and interesting biogeographical links.

Campos Rupestres (see also Chapter 9)

In the NE Brazil, campos rupestres are restricted to the plateau of the Chapada Diamantina in the State of Bahia , representing an extension of the Espinhaço Range in the State of Minas Gerais. Campos rupestres are predominantly herbaceous-shrubby vegetation that occur above 900 m , on sandstones and quartzite, usually under moister weather conditions than in the surrounding caatinga.

Vegetation in the campos rupestres is shaped in a mosaic of different physiognomies that occur side by side, reflecting different topographic conditions, depth and composition of the soil and different microclimates. Thus, in the same environment one can find extremes: from island of herbaceous vegetation on almost naked rocks to herbaceous swamps or shrubby scrub. Within typical groups of the shrubby and subshrubby stratum, representatives of families of eudicots are common. These species usually have thin branches and thick leaves, often with revolute margins and clustered in the apex of the branches. Such characteristics can be seen in species of Melastomataceae, a very diverse family in the campos rupestres of the Chapada Diamantina, which is the center of diversity for several genera, such as Marcetia, Microlicia, Cambessedesia and Lavoisiera. Other very important family in this stratum is the Asteraceae, perhaps the most diverse in the campos rupestres, with several large and endemic genera, such as Acritopappus, Agrianthus, Catolesia, Chromolaena, Lasiolaena, Lychnophora and Semiria. Leguminosae is also among the most diverse families, but the more diverse genera are different from those found in the caatinga, such as Calliandra, Chamaecrista, Mimosa and Camptosema. For the Labiatae, the Chapada Diamantina is an important center of diversity for genera like Eriope and Hyptis.

In the herbaceous stratum, families of monocots are predominant. A very diverse family is Orchidaceae, with several species growing on rocks, such as: Sophronitis (= Laelia), Cattleya, Epidendrum and Encyclia; in other environments, species of these genera occur as epiphytes. In swampy areas, there is great abundance of species of Habenaria. Besides the orchids, the Chapada Diamantina is an important center of diversity for the family Eriocaulaceae, particularly for the genera Paepalanthus, Syngonathus and Actinocephalus. Inflorescences of these plants are commercialized as ‘dry flowers’, being known popularly as everlastings. Velloziaceae (‘canelas-de-ema’) and Xyridaceae are other two families of monocots whose main center of diversity is also in campos rupestres.

One of the main biogeographical characteristics of the campos rupestres are their high local (alpha) diversity and also the high diversity among areas (beta diversity). For this reason, each surveyed area of campos rupestres reveals a particular group of species that does not occur in any other area. Good examples of this fact can be found in two floras recently published. The Flora of the Pico das Almas (in the region of Rio de Contas) surveyed 1,044 species in an area of 170 km² (what corresponds to a square with only 13 km in each side). Another survey carried out in the region of Catolés resulted in 1,713 species in an area of 667 km 2 (equivalent to a square of only 25.8 km in each side). Although being apart by only 80 km in a straight line, the areas of Catolés and Pico das Almas share only 614 species, being therefore 1,086 species exclusive of Catolés and 435 exclusive of Pico das Almas 8. That is why it is very hard to estimate the number of species in the campos rupestres of the Chapada Diamantina before a larger coverage of inventories. The available data (the ones mentioned above, plus the surveys at Morro do Pai Inácio and Serra da Chapadinha ) have already registered more than 2,700 species of angiosperms.

Importance to Man

Plant species from the Brazilian Semi-arid are an important resource to human populations, mainly to the ones who live in the caatinga. The ‘sertanejos’, native inhabitants of caatinga, are able to survive the hard conditions imposed by the caatinga because of their ability to interact with the environment, taking from it a substantial part of their bare necessities. Most of the animal farming in the caatinga is extensive and the animals, particularly goats and cattle, feed on several native species of legumes, grasses and ‘velames’ (species of Croton). Besides that, the main source of energy is the wood from several species of plants.

Traditional medicine is very strong among the sertanejos and most medical products are teas and unguents made directly from several native plants of the caatinga. Within the edible ones, it is worth mentioning fruits such as ‘umbu’ (Spondias tuberosa) and ‘licuri’ (Syagrus coronata).

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