Streptocarpus redefined to include all Afro-Malagasy Gesneriaceae: Molecular phylogenies prove congruent with geographical distribution and basic chromosome numbers and uncover remarkable morphological homoplasies

摘要

The taxonomy of the African, Madagascan and Comoro Island (Afro-Malagasy) Gesneriaceae attracts a large amount of interest given the horticultural importance of Cape Primroses (Streptocarpus) and African Violets (Saintpaulia). Earlier studies indicated that the Afro-Malagasy genera form a strongly supported clade, and recent classifications have included some of the genera within an expanded Streptocarpus. Given the global importance of this group, we carried out a comprehensive molecular phylogenetic analysis of all Afro-Malagasy genera in subfamily Didymocarpoideae, tribe Trichosporeae, subtribe Streptocarpinae, to investigate species relationships in these genera as the basis for a new classification. Phylogenetic analyses of the nuclear ribosomal spacer (ITS, 5S NTS) and chloroplast intron and spacer regions (rpl20-rps12 spacer, trnL intron, trnLF spacer) of 226 samples were performed, including all Streptocarpinae genera, except the monotypic Nodonema. The molecular phylogenies demonstrate that the genera with non-twisted fruits are nested within Streptocarpus which has twisted fruits. Two main clades were found, one comprising herbaceous caulescent Streptocarpus that also included Saintpaulia, the caulescents Hovanella and Schizoboea, and the unifoliates Acanthonema and Trachystigma. The second clade comprises the woody caulescents and acaulescent Streptocarpus, Colpogyne and Linnaeopsis. Altogether, twelve well-supported subclades can be recognized, each with a combination of distinct morphological characteristics. A new classification of tribe Streptocarpinae, de facto Streptocarpus, is presented, retaining the two subgenera, Streptocarpus and Streptocarpella, and dividing them into five and seven sections respectively. Nodonema is attributed to subg. Streptocarpus for morphological reasons. The former genus Saintpaulia is classified as Streptocarpus subg. Streptocarpella sect. Saintpaulia with ten species recognized.