The African Gesneriaceae belong to two subtribes of the Old World subfamily Didymocarpiodeae. Epithema tenuis is the only species that belongs to tribe Epithemateae, subtribe Epithematinae, and is the only non-Streptocarpus gesneriad species on the African continent. All of the other gesneriad species in Africa and Madagascar belong to the now redefined and enlarged genus Streptocarpus in the tribe Trichosporeae, subtribe Streptocarpinae:
- Family Gesneriaceae Rich. & Juss.
- Subfamily Didymocarpoideae Arn.
- Tribe Trichosporeae Nees
- Subtribe Streptocarpinae Ivanina
- Genus Streptocarpus Lindl.
- Subtribe Streptocarpinae Ivanina
- Tribe Trichosporeae Nees
- Subfamily Didymocarpoideae Arn.
The type species of the genus is Streptocarpus rexii because it was the first species in the genus to be named (Lindley, 1828), and its twisted seed capsules led to the name Streptocarpus. This type of twisted capsule became a defining feature of the genus.
However there were species in Africa that were similar in morphology to Streptocarpus that did not have twisted seed capsules that were not included in Streptocarpus, and in Asia there were species with twisted capsules that were included in Streptocarpus on that basis. DNA analyses have now clarified the twisted versus non-twisted seed capsule issue in the genus Streptocarpus (Nishii et al., 2015). It appears that all members of the African Gesneriaceae, except Epithema tenuis in the subfamily Epithemateae, should be included in the genus Streptocarpus. Those with twisted seed capsules from Asia which were originally included in the genus (the former Streptocarpus clarkeanus, and a few others) fall outside of the genus and have been taxonomically moved to other Asian genera.
All of the species originally described as Saintpaulia Wendl. (1893) have seed capsules that are short and simply cannot twist, this being the reason why they were not originally described as Streptocarpus. However, DNA evidence has now shown that they should be included in Streptocarpus (Nishii et al., 2015); additional detail can be found in our article on Saintpaulia.
The taxonomic changes described in Nishii et al. (2015) therefore make Streptocarpus a truly African and Madagascan (including the Comoros Islands) genus. Streptocarpus has no members that are to be found on other continents or island groups.