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| Petalidium sebrabergense Swanepoel & A.E.van Wyk, in Swanepoel et van Wyk, 2025. Photographs by W. Swanepoel. |
Abstract
Petalidium sebrabergense, first collected in May 2024 and easily mistaken for P. cirrhiferum, is described here as a new species. It is a range-restricted species, only known from Namibia’s Zebra Mountains, within the Kaokoveld Centre of Endemism. It typically grows on plains, hillsides, and along ephemeral riverbeds and drainage lines, primarily in soils derived from anorthosite and gabbro of the Kunene Igneous Complex. Key distinguishing features for P. sebrabergense include the pale green appearance of the plants, vegetative parts with indumentum of dense, simple, multi-cellular stalked glandular trichomes, frequently interspersed with widely spaced eglandular simple and bifurcate trichomes, often with some leaves additionally bearing sparsely branched dendritic trichomes. The flowers are borne in racemose dichasia and are notable for having the corolla lobes lilac or mauve, with both sides concolorous. A comparison of key morphological features distinguishing P. sebrabergense from P. cirrhiferum, its closest look-alike, is provided. Brief comparisons are also made with P. huillense, P. subcrispum, and P. welwitschii, species with which it can be confused, particularly in herbarium specimens. Based on IUCN Red List criteria, a provisional conservation status of Critically Endangered (CR) is recommended for the new species.
anorthosite, endemism, Epupa, flora, Kaokoveld Centre of Endemism, Kunene Igneous Complex, Kunene Region, Kunene River, Ruellieae, Swartbooisdrif, taxonomy, ultramafic rocks, Zebra Mountains, Eudicots
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| Petalidium sebrabergense. Habit and leaf variation. A. Dwarf shrub ca. 400 mm high with relatively narrow leaves, growing among dark rocks of leucotroctolite. B. Dwarf shrub ca. 250 mm high with relatively broad leaves, growing in whitish anorthosite-derived soil. Habitat and habit. A. Dwarf shrubs in foreground with bright green foliage following recent rains; in open shrub and tree savanna of inter-mountain valley on whitish soil derived from anorthosite. B. Spreading dwarf shrubs in an ephemeral stream bed on whitish anorthosite-derived soil. Photographs by W. Swanepoel. |
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| Petalidium sebrabergense. Morphology of flowers. A. Shoot with relatively narrow leaves and flowers. B, C, D, E. Flowers in front view, each from a different plant to show variation. Corolla lobes are lilac or mauve (pale violet), both surfaces concolorous. F, G. Flower in side view; bracteoles abaxially with numerous simple multi-cellular stalked glandular trichomes up to 2 mm long (not or barely visible to the naked eye), but lacking dendritic trichomes. Photographs by W. Swanepoel. |
Petalidium sebrabergense Swanepoel & A.E.van Wyk, sp. nov.
Diagnosis:—A woody dwarf shrub up to 0.75 m tall, morphologically most similar to Petalidium cirrhiferum, differing by lacking dendritic trichomes on stems (vs. dendritic trichomes present); indumentum on leaves with trichomes sparsely to densely scattered (vs. appearing matted or floccose); leaf lamina lanceolate (sensu Lindley’s definition [Beentje 2016]), oblanceolate or elliptic (vs. lanceolate [sensu Lindley], ovate or narrowly ovate); bracteoles with indumentum abaxially lacking dendritic trichomes (vs. longstalked dendritic trichomes present); corolla lobes adaxially lilac or mauve (pale violet) (vs. heliotrope, magenta or purple-red [bright violet or red]).
Etymology:—The specific epithet refers to the Zebra Mountains (Fig. 1), known as Sebraberge in Afrikaans, located in northwestern Namibia, where Petalidium sebrabergense is exclusively found.
Wessel SWANEPOEL, Abraham E. VAN WYK. 2025. Petalidium sebrabergense (Acanthaceae), A New Species from Namibia. Phytotaxa. 728(1); 17-30. DOI: doi.org/10.11646/phytotaxa.728.1.2 [2025-11-11]
