Abstract
Sida is one of most heterogeneous genera of Malvaceae and one of the richest in species inside Malvoideae. It comprises about 200 pantropical and American species with a few of these extending into the temperate regions, 112 of them occurring in Brazil. Studies on the taxonomy of Sida in this country are few. In the State of Pernambuco, the genus is represented by 24 species widely distributed in all of the four major phytogeographical zones (littoral, agreste, savannah and caatinga). It occurs in different localities and habitats, such as natural and disturbed areas or in urbanized areas. This synopsis includes a taxonomic key, new synonyms, lectotypes and new records, description of one new species (Sida pernambucensis), illustrations, and brief comments of morphology, habitat and geographical distribution.