A taxonomic revision of the genus Pyrenacantha Wight (Icacinaceae) from Madagascar is presented, including a key to species. The study of morphological characters allows the recognition of nine species, all endemic to Madagascar, five of which, P. ambrensis, P. andapensis, P. perrieri, P. rakotozafyi and P. tropophila, are newly described here. Pyrenacantha ambrensis is a woody liana that possesses papyraceous leaves with margins that are not dentate, infructescences that are robust but of a small size and axillary or situated just below larger leaves and fruit, ovoid, orange-brown and with a long stipe. Pyrenacantha andapensis is a woody liana that has spherical fruits of a dark brown colour and a relatively long stipe. Pyrenacantha perrieri is a gracile herbaceous liana that possesses solitary male inflorescences, sessile male flowers and female inflorescences reduced to 1-3 fasciculated flowers. Pyrenacantha rakotozafyi is a gracile herbaceous liana that possesses solitary female inflorescences with a straight and vigorous rachis carrying widely spaced flowers. Pyrenacantha tropophila is a woody liana that possesses stigmata that are divided into four glandulous protuberances and large, smooth brown-coloured, shortly stiped fruits.
Icacinaceae, Pyrenacantha, Madagascar, new species