Petalidium matupaense (Acanthaceae), a new species from Angola

Petalidium matupaense, first collected in May 2019, is here described as a new species. It is a range-restricted species, only known from the mountainous region bordering the Cunene River in southwestern Angola in the Kaokoveld Centre of Endemism. The species grows amongst boulders on hillsides of the Kunene Igneous Complex, along ephemeral riverbeds and in intermontane valleys. Diagnostic characters for P. matupaense include its slender stems and the dense white indumentum of mainly short-stalked dendritic trichomes on the vegetative parts (glabrescent with age) and inflorescences, giving a matted appearance. The flowers are distinctive in having all lobes similarly coloured adaxially, carmine, peach, vermillion (orange-red), or mauve, the anterior lobe with two yellow narrowly triangular nectar guides, and all lobes discolorous in being abaxially paler or cream-brown. A comparison of key morphological features distinguishing Petalidium matupaense from P. cirrhiferum and P. sebrabergense, its morphologically most similar relatives, is provided. Based on IUCN Red List criteria, the species is provisionally assessed as Endangered (EN).