A floristic survey was carried out in the Biological Reserve of Serra Negra, between the municipalities of Inajá and Floresta (8º35'-8º38' S and 38º02'-38º04' W), in order to assess the floristic relationship between two sites, a dense forest on the plateau, and an open forest, located on the southern scarp. Nineteen trips were accomplished to collect Bryophyta, Pteridophyta and Magnoliophyta. 319 taxa, 255 on the plateau and 117 on the southern scarp were registered. The presence of distinct abiotic factors, the southern scarp being has drier than the plateau, justify the floristic difference. In spite of the low similarity level between the two sites (12,5%), the cluster analysis grouped both with a other surveys realized in other montane forests in the northeast region. The dense forest has many species with a wide distribution in the Amazon and Atlantic regions, while in the open forest some species are more related with the thorny decidual woodland (caatinga), white others have a wide distribution in neotropical forests.
Upland forest; thorny decidual woodland; floristic; semi-arid; northeast of Brazil
