A taxonomic revision of Pentzia (Asteraceae, Anthemideae) I: the P. incana group in southern Africa, including the description of the new species P. oppositifolia Magee

A taxonomic study is presented of an informal group of morphologically similar species, referred to here as the Pentzia incana group. The group is distinguished by the combination of smaller (≤ 8 mm broad), shortly-pedunculate, solitary, terminal capitula, often with 1 to 3 additional capitula from the leaf axils below; ovate to broadly elliptic involucral bracts with broadly membranous margins that apically enclose the young capitula; absence of resin canals in the involucral bracts; and general absence of secondary basal lobes in the lower and middle leaves. A key to all six species in the P. incana group is presented, as well as a taxonomic revision of the four southern African species. Six species are recognised, one of which, Pentzia oppositifolia Magee, is described as new. Pentzia bolusii, a species known only from a single depauperate specimen, is reduced to synonymy under P. incana. Four of the species within the P. incana group are endemic to southern Africa (P. calcarea, P. calva, P. incana and P. oppositifolia), one to Somalia (P. somalensis) and the other to Yemen (P. arabica). The species were found to differ in the arrangement of the leaves and capitula, the shape of the involucre, and the presence or absence of a pappus. Differences in the fruit anatomy were also observed.

► A key to all six species within the Pentzia incana group.
► Description of a new species, Pentzia oppositifolia Magee.
► Reduction of Pentzia bolusii into synonymy with P. incana.
► Distribution of P. calva reported to extend into South Africa for the first time.
► Fruit anatomical differences observed.