Revision of the Malagasy species of the genus Tricalysia (Rubiaceae)

The Malagasy representatives of the large African genus Tricalysia (tribe Coffeeae s.l.) are revised. Three Malagasy species were hitherto recognized in the genus, namely T. cryptocalyx, T. madagascariensis, and T. ovalifolia. In this study, two species, T. boiviniana and T. leucocarpa, are transferred from the genus Hypobathrum and seven new species and two new subspecies are described, raising the species number for Tricalysia to a total of 12. This marked increase in species number is a recurring pattern for many Malagasy genera in systematically poorly known families such as Rubiaceae. All the species are described in detail and illustrated, and a list of exsiccatae and a distribution map are provided. Furthermore, the characters of the Malagasy taxa are compared with those of the continental African species, and their infrageneric status is discussed. With the exception of T. ovalifolia, a member of subgenus Empogona, all Malagasy species belong to subgenus Tricalysia. Because of their unisexual flowers, these species cannot be accommodated within one of the four existing sections in subgenus Tricalysia. A new section, Androgyne, is therefore recognized. (c) 2007 National Botanic Garden of Belgium. Journal compilation (c) 2007 The Linnean Society of London.