Streptocarpus petrodoxa (Gesneriaceae), a new species from the granite whalebacks of Mpumalanga Province, South Africa

Streptocarpus petrodoxa is described from the granite whalebacks of Mpumalanga Province, South Africa. The species occurs in a highly restricted habitat beneath large granite boulders on inselbergs near White River, where it occupies shaded crevices in shallow, sandy lithosols derived from weathered granite. Comparisons with closely related taxa, S. pole-evansii and S. denticulatus, reveal distinct differences in leaf size, indumentum, corolla morphology and style orientation. All parts of the plant are covered with orange-red pigment granules, called dunnione, placing the species within a small group of Streptocarpus known to produce this chemical compound. Given its highly localised distribution, specialised habitat, and an estimated population of less than a thousand individuals, the species is assessed as Critically Endangered (CR B1ab(iii)+B2ab(iii)). A dichotomous key distinguishing S. petrodoxa, S. pole-evansii, S. denticulatus and S. dunnii is included.