Recent phylogenetic investigations of the Violaceae have shown that Hybanthus s. l. was polyphyletic, consisting of nine macromorphologically and geographically distinct clades. For this study the "Hybanthus enneaspermus" clade was chosen for intensive examination. Morphological traits were identified that distinguish it fully from other clades of Hybanthus, and the clade was described as a new segregate genus, Afrohybanthus.
Afrohybanthus is a violet group distributed broadly across the Old World tropics and is composed of annual and perennial herbs, woody subshrubs and shrubs, with a center of species diversity in eastern Africa. The group as a whole has never been taxonomically scrutinized with the few previous treatments being restricted in scope to floras of narrow geographic regions. Study of extensive herbarium collections distinguished all taxa of Afrohybanthus from other hybanthoids and other Violaceae by their zygomorphic corollas with the bottom (anterior) petal substantially longer than the lateral and upper ones, differently shaped and often strongly differentiated into an abruptly expanded blade and claw, with a noticeable spur at the base; usually free stamens; staminal glands often with rectangular body and attached medially or apically on the filament; three-valved capsules with usually 3-4 seeds per valve; and unwinged ellipsoid pale yellow to honey-colored seeds that are longitudinally ribbed and/or foveolate (or rarely smooth).
Phylogenetic reconstructions were inferred from chloroplast trnL intron, trnL-F spacer, and nuclear Internal Transcribed Spacer (ITS) sequences of representatives across Afrohybanthus and outgroups, showing weedy and widespread A. enneaspermus to be a derived clade of populations distinct from several well-supported clades of many morphologically divergent narrow endemics.
For a particularly difficult group of Afrohybanthus in tropical East Africa, phenetic analyses were performed on specimens belonging to seven initial groups interpreted from qualitative morphological features and geography, to help determine species boundaries and clarify variation patterns of populations in the region. Analyses revealed four distinct species in the region, one corresponding to A. enneaspermus (L.) Flicker distributed across much of the paleotropics, and three species narrowly distributed in the region with divergent floral, fruit and seed traits.
Phylogenetic evidence for a number of distinct clades of differentiated taxa, combined with expanded morphological characterizations, reject previous hypotheses that the group is represented by one highly polymorphic A. enneaspermus and several infraspecific taxa, differing largely in extremes of leaf morphology, plus a few restricted species. Rather, the collective results demonstrate that Afrohybanthus consists of one very broadly distributed, weedy A. enneaspermus, and many morphologically distinctive, narrowly endemic species, all differing in various features of floral, capsule and seed morphology and in some cases distinctive vegetative features. The resulting taxonomic synopsis of Afrohybanthus recognizes 23 distinct species, with five new combinations elevating infraspecific names to species rank, as well as four undescribed species.