Hekistocarpa (Rubiaceae): a member of an emended tribe Virectarieae

Abstract.

 The monospecific genus Hekistocarpa (Rubiaceae) is restricted to the rainforest region of Cameroon and Nigeria. Traditionally, it has been placed in the tribe Hedyotideae, subfamily Rubioideae, from which it differs in the absence of raphides. Cladistic analyses of nucleotide sequences from the rbcL gene and the rps16 intron support a group comprised of Hekistocarpa, Tamridaea, and Virectaria (subfamily Ixoroideae s. l.). This clade is the sister group of Sabicea plus Pseudosabicea. Although Sabicea, Pseudosabicea, Tamridaea and Virectaria have been proposed to belong to a reformed tribe Sabiceeae; it is proposed here that Sabiceeae should be restricted to comprise Sabicea and allies, and that Hekistocarpa, Tamridaea, and Virectaria should be referred to an emended tribe Virectarieae. The tribes Virectarieae and Sabiceeae are more easily characterized morphologically than a more broadly circumscribed tribe Sabiceeae (including Virectaria, Hekistocarpa, and Tamridaea). A detailed description is given for Hekistocarpa, including external morphology, reproductive anatomy, and pollen morphology.