Hydrogaster is a monotypic genus of Malvaceae (Grewioideae), represented by H. trinervis, a canopy tree endemic to the Brazilian Atlantic Forest. Despite its description in 1935, the species has remained poorly documented and underrepresented in floristic surveys, with confirmed records restricted to the states of Bahia, Espírito Santo, and Rio de Janeiro. Its distribution, ecology, and morphological variation has therefore remained fragmentary. This study aims to clarify the circumscription of H. trinervis and provide an updated taxonomic framework for the species. We conducted an integrative study combining the review of herbarium collections, field observations, and monitoring of cultivated specimens. We provide an updated morphological description of H. trinervis, accompanied by a botanical illustration based on living specimens, together with comparative notes on morphologically similar taxa. In addition, we present lectotypification and nomenclatural remarks, as well as phenological and ecological observations and a preliminary conservation assessment. Our results expand the knowledge on this species of the Atlantic Forest flora, highlighting its restricted distribution and reinforcing the importance of conservation efforts for the maintenance of its populations.
Ferreira et al. (Thu,) studied this question.
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