Subgeneric and sectional classification

The big DNA analysis of Nishii et al. (2015), in which were included representative species from across Streptocarpus and Saintpaulia as well as other minor genera, revealed new patterns of phylogenetic relationships. Based on this new phylogeny the classification of species within Streptocarpus was changed, achieving much greater clarity. The phylogeny indicated that there are two clades containing respectively two sections (Hova and Parasaintpaulia) and three sections (Colpogyne, Lignostreptocarpus and Plantaginei), that are found only in Madagascar whilst all of the other sections are found in Africa.

If this is analyzed with biogeographic methods, this gives support to the hypothesis that there were two independent dispersals of Streptocarpus to Madagascar from Africa. Again, this idea is not new, as this was proposed by Hilliard and Burtt many years ago.

In the new classification of genus Streptocarpus by Nishii et al. (2015), the genus still subdivides into the two previously recognized subgenera but with new circumscriptions and 12 newly defined sections.

  • Subgenus Streptocarpella:
    • Section Carnosifolii
    • Section Caulescentes
    • Section Hova
    • Section Parasaintpaulia
    • Section Saintpaulia
    • Section Schizoboea
    • Section Trachystigma
  • Subgenus Streptocarpus:
    • Section Colpogyne
    • Section Lignostreptocarpus
    • Section Plantaginei
    • Section Protostreptocarpus
    • Section Streptocarpus
Phylogenetic relationships of the subgenera and sections of genus Streptocarpus (adapted from Nishi et al., 2015). The biogeography, floral types, habit and capsule characters are shown in columns to the right. The broken line at the base of the Section Plantagenei indicates that this relationship is poorly supported. The letters a-k next to the section names indicates the order in which the Sections are described hereafter. Mad =Madagascar, cau = caulescent, lab = labellanthus, rhiz = rhizomatous, ros = rosulate, St. = Saintpaulia; str = straight, tw = twisted, uni = unifoliate.

The two subgenera have certain distinctive characteristics. Streptocarpus usually have unifoliate or rosulate leaf structures emerging from the base of the plant, while Streptocarpella species usually have branching stems with conventional leaves. Streptocarpus species largely have reticulate (netted) seeds and 16 chromosomes, whilst Streptocarpella species largely have verruculose (warted/bumpy) seeds and 15 chromosomes. More detailed descriptions of each of the subgenera and their sections are given hereafter. For a full species listing, see Appendix 1.

Seeds from plants within subgenus Streptocarpus (left) have reticulate (netted) seeds while those in subgenus Streptocarpella have verruculose (bumpy/warty) seeds, including seeds of the historical Saintpaulia group. This is one of the morphological characters that suggest that the two subgenera are distinct, and that Saintpaulia is properly assigned to Streptocarpella, both of which have been confirmed by subsequent genetic analysis. Photos courtesy of Royal Botanical Garden, Edinburgh.

In the Section pages that follow, species have been placed in Sections based on genetic analyses by Nishii et al (2015), or on morphological grounds as indicated:

* by Nishii et al (2015)

** by the present author, Dirk Bellstedt, based on new species descriptions after 2015