Taxonomic revision of Rinorea ilicifolia (Violaceae) from Africa and Madagascar

摘要

The uncertain taxonomic circumscription between Rinorea ilicifolia (Welw. ex Oliv.) Kuntze and R. spinosa (Boivin ex Tul.) Baill. has led to considerable confusion when attempting to identify the two species. The plants from mainland Africa have typically been determined as R. ilicifolia while the plants in Madagascar and the Comoro Islands have been variously assigned to R. spinosa, R. ilicifolia, or R. ilicifolia subsp. spinosa (Boivin ex Tul.) Grey-Wilson. A third taxon from east Africa, R. ilicifolia var. amplexicaulis Grey-Wilson, has auriculate leaf bases and a mostly discrete distribution from R. ilicifolia, suggesting a greater degree of divergence than is indicated by its taxonomic rank of variety. To better understand the circumscription among these three taxa, we performed multivariate and discriminant analyses of six quantitative variables measured from herbarium specimens. Based on results from these analyses, we deemed there was insufficient morphological divergence to maintain R. ilicifolia and R. spinosa as separate species. Instead, we recognise a single species, R. ilicifolia, composed of three subspecies: R. ilicifolia subsp. ilicifolia in mainland Africa, R. ilicifolia subsp. spinosa in Madagascar and the Comoro Islands, and R. ilicifolia subsp. amplexicaulis (Grey-Wilson) Wahlert, comb. et stat. nov. from Tanzania and Burundi. Here we provide a taxonomic revision of R. ilicifolia, a distribution map and preliminary risk of extinction assessment using IUCN Red List categories and criteria for the three subspecies. We also propose a change of status for Rinorea [unranked] Ilicifoliae Engl. to the rank of section, an action supported by phylogenetic and morphological evidence. The new section includes R. ilicifolia and 13 other taxa from mainland Africa. Lectotypes are designated for the section and for Alsodeia spinosa Boivin ex Tul., and a second-step lectotype is selected for Alsodeia ilicifolia Welw. ex Oliv.