Sida antonioi: a new species of Sida sect. Malacroideae (Malvoideae, Malvaceae)

We describe Sida antonioi, a new species of Sida sect. Malacroideae, based on herbarium specimens and in situ observations. Previously misidentified as other species within the section, S. antonioi is distinguished by its dimorphic stipules on the stem, apical inflorescence, calyx with long yellow simple trichomes on the lobe apex, and non-muricate mericarps. The species is endemic to the Atlantic Forest biome in southeastern Brazil. We provide a detailed taxonomic description, a geographic distribution map, and a preliminary conservation assessment. Additionally, we compare its diagnostic characters with those of three morphologically similar and geographically proximate species within Sida sect. Malacroideae.