Petalidium etendekaense (Acanthaceae), a new species from Namibia, with notes on the taxonomic identity of P. glutinosum

Abstract

Petalidium etendekaense, previously mistaken for P. glutinosum and P. variabile, is now described as a new species. The name P. pilosibracteolatum is considered synonymous with the older P. glutinosum, the latter of which is also lectotypified. The newly described species is currently only known from the vicinity of Bergsig and slightly further west towards the Skeleton Coast National Park in the Kaokoveld Centre of Endemism, northwestern Namibia. It typically grows on hillsides and along ephemeral riverbeds, primarily in soils derived from Etendeka Group basalt. Diagnostic characters for P. etendekaense include its tomentose-strigulose indumentum, the inflorescence main axis and secondary branches that invariably become spiny with age, and a corolla with an ovate front lobe that is longer than it is wide. Additionally, all lobes of the corolla exhibit similar colours, ranging from dark burgundy to carmine to pink towards the apices. A comparison of some morphological features is provided to differentiate Petalidium etendekaense from P. glutinosum and P. variabile. Based on the IUCN Red List categories and criteria, we conducted a conservation assessment, resulting in the new species being classified as of Least Concern (LC).