Ixora kalehensis, a new Rubiaceae species from the Democratic Republic of the Congo

Ixora L. is the only genus in the tribe Ixoreae (supertribe Ixoridinae, subfamily Cinchonoideae, family Rubiaceae). Previously, this tribe also contained a number of small satellite genera, notably Captaincookia N.Hallé from New Caledonia, Doricera Verdc. and Myonima Comm. ex Juss. from the Mascarenes and Versteegia Valeton from New Guinea and the Solomon Islands. After phylogenetic studies by Mouly et al. (2009a) these small genera were placed into synonymy with Ixora. Ixora is a large rain forest genus of shrubs and small trees and has a pantropical distribution. A majority of its c. 530 species (Davis et al. 2009) occur in Asia and Oceania, but Ixora is also represented in South and Central America and in Africa. More than 85 species of Ixora occur in Africa, c. half of those in Madagascar (De Block 2007, 2008, 2014a, 2014b), 37 in continental Africa (De Block 1998) and six species in the Mascarenes and the Seychelles (Mouly et al. 2009b). In continental Africa, Ixora is easily recognized by the following characters: petioles articulate; inflorescences terminal, with branching trichotomous, articulate and bracteolate; flowers narrowly tubular, 4-merous; aestivation contorted; stigma bilobed; ovary bilocular with a single ovule per locule; fruits drupaceous, containing two seeds; seeds hemispherical or hemi-ovoid with a large adaxial excavation (De Block 1998). The representatives from the Indian Ocean Islands usually have the same characters but a few species differ by lacking the articulate branching in the inflorescence (e.g. I. pudica Baker from Mauritius) or by being 3–7-locular with the stigma 3–7-lobed, and the seeds 3–7 per fruit and not hemispherical or hemi-ovoid in shape (e.g. I. quadrilocularis De Block from Madagascar and I. borboniae Mouly & B.Bremer, formerly known as Myonima obovata Lam., from Mauritius and Reunion) (Verdcourt 1983, De Block 2014a). In the most recent revision of the genus in continental Africa, 37 Ixora species were recognized and two further taxa were mentioned as possibly new: Ixora sp. “Kalehe” from D.R. Congo and Ixora sp. “Waka” from Gabon (De Block 1998). Ixora sp. “Kalehe” was only known from one specimen collected by Troupin in 1957 west of Lake Kivu.