Taxonomic revision of Neotropical Mendoncia Velloso ex Vand. (Acanthaceae, Thunbergioideae, Mendoncieae)

Taxonomic revision of Neotropical Mendoncia Velloso ex Vand. (Acanthaceae, Thunbergioideae, Mendoncieae)

Mendoncia Velloso ex Vand. (Acanthaceae, Thunbergioideae, Mendoncieae) is a genus composed of approximately 90 species occurring in the tropical regions of the old and new world. The Neotropical region is the most diverse in number of species, that are distributed from southeastern Mexico to Brazil and Bolivia, inhabiting mainly humid forests, with the Amazon being the greatest center of diversity of the genus, with more than half of the species. Representatives of Mendoncia are recognized for having a unique set of characters among the Acanthaceae, being voluble climbers, with a pair of well-developed bracteoles that partially cover the corolla and the fruits, a generally reduced calyx and drupaceous fruits. Phylogenetic studies point to the subfamily Thunbergioideae and Mendoncia as monophyletic groups. An extensive literature review was carried out, especially the study of the protologues and of other relevant work focusing in the Acanthaceae. The analysis of the specimens was based field expeditions coupled with studies of South and North American and European herbaria, always prioritizing the analysis of the nomenclatural types. Based on these studies, it was possible to reestablish the type species of the genus, which had previously been erroneously designated (Chapter I). From the existing monographs and floras for the genus that mention the importance of the indumentum for the subgeneric classification, the need arose to investigate the identity of the trichomes found both in new and old world Mendoncia. Images taken with the aid of optical and scanning microscopy were prepared and it was concluded that the trichomes have taxonomic value at a specific level, but did not corroborate Mendoncia's subgeneric classification (Chapter II). Several field expeditions were carried out between 2019 and 2022, aiming to increase the sampling of species and study populations in the field. In the early phase of the programme (2020) it was necessary to conclude the monograph for the Flora of Brazil 2020, as this large collaborative project had a more urgent target than the present work (Chapter III). Once all data were gathered the circumscription of species was worked out and a revised taxonomy of Mendoncia including taxonomic novelties, interactive identification key, information on morphology, phenology and geographic distribution was produced.

70 species are treated here, starting from 88 names initially accepted for the Neotropics, and the necessary nomenclatural changes are presented (Chapter IV). During the trip to Colombia, a new species was discovered and is currently submitted for publication (Chapter V). The circumscription and stabilization of Mendoncia's taxonomy resulted in a better understanding of the geographic distribution of taxa, providing a reliable alpha-taxonomy that will enable future studies in this genus.