Abstract The biota of the humid mountain ranges of the Brazilian semiarid is still poorly understood. In order to fill this scientific gap, we carried out an extensive survey along altitudinal ranges (400m - 1,000 m) on both the windward and the leeward slopes of the Baturité Mountain Range, in the state of Ceará state. We registered 400 plant species and 92 families. The Myrtaceae (36 spp.), Fabaceae (25 spp.), Rubiaceae (20 spp.) and Bromeliaceae (15 spp.) families predominated on the windward slope; while Fabaceae (19 spp.), Myrtaceae (14 spp.) and Euphorbiaceae (11 spp.) were the most abundant on the leeward slope. As we expected, the species richness of trees, shrubs, subshrubs, epiphytes and terrestrial herbs was positively correlated with the altitude (R2 > 0.60). Above 800 m, we registered 273 species exclusive to the windward slope, 81 exclusive to the leeward slope, and 46 shared species. Therefore, management actions must consider the spatial heterogeneity, distribution and taxa richness.

Resumo Para verificar se a composição florística constitui unidades discretas ou contínuas ao longo de um gradiente topográfico foram analisadas três fitofisionomias (caatinga sobre altitudes de 300 a 500 m, floresta decídua sobre altitudes de 500 a 700 m e carrasco sobre atitudes de 700 m) sobre classes de solos distintas no semiárido setentrional do Nordeste do Brasil. Em cada fisionomia foi realizado o levantamento das espécies, as quais foram classificadas em formas de vida e de crescimento. A riqueza de espécies foi maior na floresta decídua (250) do que no carrasco (136) e na caatinga (137). A caatinga apresentou poucas espécies em comum com as fitofisionomias de carrasco ou de floresta decídua (6 e 18 espécies). A maior sobreposição de espécies ocorreu entre a floresta decídua e o carrasco, 62 espécies. Foram exclusivas da caatinga, floresta decídua e do carrasco, 104, 161 e 59 espécies, respectivamente. Quanto às formas de crescimento, nas fisionomias sobre relevo sedimentar com Latossolo e Arenosolo predominaram espécies lenhosas: 124 na floresta decídua e 68 no carrasco. Na caatinga sobre relevo do embasamento cristalino com predominância de Planossolo, a maior riqueza de espécies (69) foi de ervas. Na análise comparativa do espectro biológico com outras formações brasileiras, o de caatinga se destacou dos demais, constituindo uma unidade individualizada pela maior proporção de terófitos e caméfitos. Em relação à flora das três fisionomias, objeto deste estudo, pode-se afirmar que a da caatinga representa uma unidade discreta.

Abstract To test whether the flora is organized in discrete or continuous units along a topographic gradient, three physiognomies were assessed on different soil classes in a semi-arid region of northeastern Brazil: caatinga (xeric shrubland) at altitudes from 300 to 500 m, deciduous forest at altitudes from 500 to 700 m and carrasco (deciduous shrubland) at 700 m. In each physiognomy a species inventory was carried out, and plants were classified according to life- and growth-forms. Species richness was higher in the deciduous forest (250) than in the carrasco (136) and caatinga (137). The caatinga shared only a few species with the carrasco (6 species) and the deciduous forest (18 species). The highest species overlap was between the deciduous forest and the carrasco (62 species). One hundred and four species occurred only in the caatinga, 161 only in the deciduous forest and 59 only in the carrasco. Woody species predominated in physiognomies on sedimentary soils with latosol and arenosol: 124 species occurred in the deciduous forest and 68 in the carrasco. In the caatinga on crystalline basement relief with predominance of planosol, herbs showed the highest species richness (69). Comparing the biological spectrum of Brazilian plant life-forms, the caatinga stood out with higher proportion of therophytes and chamaephytes. Considering the flora of the three phytophysiognomies studied here, we can affirm that the caatinga is a discrete floristic unit.