A recircumscription of Jacobsenia (Aizoaceae): Re-instating Drosanthemopsis, with two new quartz-endemics from Namaqualand, South Africa and sinking Knersia

Abstract

The species of Jacobsenia are succulent shrubs which are almost exclusively endemic to patches of quartz-gravel in the arid, winter-rainfall region of South Africa. With data from ten chloroplast markers we show that Jacobsenia is polyphyletic in its current circumscription and that J. vaginata should be excluded from it. We place Jacobsenia vaginata once more in Drosanthemopsis as D. vaginata. Two new species are shown to be closely related to D. vaginata and are also placed in Drosanthemopsis as D. bella Klak sp. nov. and D. kwaganapensis Klak sp. nov. The recently described monotypic Knersia is sister to the three species of Drosanthemopsis and is now included in it. All four species share the unique, antler-like protrusions of the epidermal cells on the leaves. The expanded Drosanthemopsis is found in three of the six phytochoria recognized within the quartz-field flora (QFF) of southern Africa: the Knersvlakte, the Riethuis-Wallekraal and the Southern Richtersveld. Although, D. kwaganapensis and D. vaginata both occur in the Riethuis-Wallekraal phytochorion, the distributions of the four species of Drosanthemopsis do not overlap. Phylogenetic relationships, the distribution of the species of Drosanthemopsis and the assumed relative ages for the QFF support a northward “trek” of several quartz-endemic taxa in the Aizoaceae, i.e. a diversification from the Knersvlakte northwards into the Richtersveld. We provide a taxonomic treatment for the species of Drosanthemopsis (including Knersia) and Jacobsenia, including their distributions and revised generic descriptions.