We present the leaf anatomy of seven amphibious species of Aeschynomene L. (Papilionoideae, Leguminosae), interpreting their structures and ecological functions, and also, providing information on which their taxonomy can be based, especially of morphologically similar species. We evaluated Aeschynomene americana, A. ciliata, A. evenia, A. denticulata, A. fluminensis, A. rudis and A. sensitiva. The anatomy corroborates the separation of the series Americanae, Fluminenses, Indicae and Sensitivae, with the shape of the petiole, types of trichomes and quantity of vascular units in the petiole as main characteristics to delimit the species. The petiole shape varies from cylindric in A. americana, A. sensitiva and A. fluminensis, to triangular in A. evenia and quadrangular in A. rudis, A. denticulata and A. ciliata. We observed four types of trichomes: hydathode trichome, long conic trichome, short conic trichome and bulb-based trichome. The hydathode trichome was the most common, except for A. americana and A. fluminensis. Species with higher affinity with water share similar adaptive characteristics, including hydathode trichomes described for the first time for the genus. This article adds unseen descriptions for the genus and on the adaptation factors of the amphibious species.
macrophytes; Fabaceae; hydathode trichome
