Taxonomy "under construction": advances in the systematics of Apocynaceae, with emphasis on the Brazilian Asclepiadoideae

The Apocynaceae comprise approximately 5,000 species and are widely distributed. The family belongs to the Gentianales and can be easily recognized by the presence of latex and a style-head derived from the fusion of two carpels at the apex of the styles. The largest subfamily in Apocynaceae is Asclepiadoideae. Treated as the Asclepiadaceae for almost two centuries, it comprises about 3,000 species and is defined by stamens with bisporangiate anthers and pollen transferred in specialized units called pollinaria. Since the 19th century, floristic studies and taxonomic monographs have significantly contributed to the taxonomy of Brazilian Asclepiadoideae. Nevertheless, advances in understanding the internal relationships in the subfamily were not done until this millennium, with the popularization of phylogenetic studies based on molecular data and powerful computer analyses. Advances in the systematics of Apocynaceae have provided new interpretations on the morphological evolution and biogeography of the family and have led to important changes in its classification. Nevertheless, several taxonomic rearrangements are still needed and it can be said that the taxonomy of Apocynaceae is "under construction". In this article, the major taxonomic changes in the family are reviewed, with special attention given to the systematics of Neotropical groups. A cladogram of the Apocynaceae is presented, which highlights the phylogenetic position of the Brazilian genera and their diversity in number of native species. The main studies and the diversity of Asclepiadoideae in Brazil are summarized and perspectives for future research on the subfamily are presented.