 |
| Petalidium karasbergense Swanepoel & A.E.van Wyk, in Swanepoel et van Wyk, 2023. Photographs by W. Swanepoel. |
Abstract
Petalidium karasbergense, here described as a new species, is only known from the Groot Karasberge (Great Karas Mountains) in southeastern Namibia where it grows on arid hillsides in dwarf shrubland. Diagnostic morphological characters for P. karasbergense include the rigid, tapering and often spinescent distal stems and lateral branchlets, grey, grey-white or grey-black bark (white to cream when young), strigulose, glabrescent vegetative parts, oblanceolate to narrowly obovate leaves, and the free to almost free bracteole pairs (not connate at the base). A comparison of some of the more prominent features to differentiate Petalidium karasbergense from P. parvifolium, its morphologically most similar relative, and P. lucens with which its distribution range marginally overlaps, is provided. Based on IUCN Red List categories and criteria, a conservation assessment of Vulnerable VU D1 is recommended for the new species.
Keywords: desert, endemism, flora, Great Karas Mountains, Groot Karasberge, Petalidium lucens, Petalidium parvifolium, Ruellieae, taxonomy
 |
| Petalidium karasbergense, morphology of flowers, stems, and leaves. A. Flower in front view. B. Flower with bracteoles in lateral view. C. Flower viewed from below; note the bracteoles that are not connate at the base, hence the calyx is clearly visible over the whole of its length. D. Branchlet showing an open flower, persistent bracteoles, and leafy side shoots (some tapering to a spinescent tip). E. Enlarged portion of Auret 5617 in Herb. PRE showing three brachyblasts, the longest one with several phyllopodia, the latter each ca. 1 mm long. Photographs by W. Swanepoel (A–D) and A.E. van Wyk (E). |
Petalidium karasbergense Swanepoel & A.E.van Wyk, sp. nov.
Diagnosis:—A woody dwarf shrub up to 1 m tall, morphologically most similar to Petalidium parvifolium, differing in having the distal stems and lateral branchlets tapering to a blunt or spinescent apex (vs. cylindric); indumentum on vegetative parts strigulose (vs. scattered sessile glandular trichomes); young growth not glutinous (vs. covered with a glutinous secretion [glossy]); leaf lamina subconduplicate towards recurved apex (vs. flat or subreduplicate, apex slightly recurved); bracteoles free or almost free from base (vs. distinctly connate towards base), indumentum (abaxially) on bracteoles strigulose (vs. scattered sessile glands, towards base sometimes with very short stalked glandular trichomes in addition).
 |
| Petalidium karasbergense, habitat and habit. A. Plant (ca. 50 cm high) with open flower. B. Old, stunted plant showing thick, woody stem (ca. 8 cm in diameter). C. Mature plant (ca. 80 cm high) in habitat; surrounded by sandstone rocks of the Nama Group. Photographs by W. Swanepoel. |
Etymology:—The specific epithet refers to the Groot Karasberge in southeastern Namibia, the mountain complex to which the new species is confined.
Wessel Swanepoel and Abraham E. van Wyk. 2023. Petalidium karasbergense (Acanthaceae), A New Species from Namibia. Phytotaxa. 609(1); 1-9. DOI: 10.11646/phytotaxa.609.1.1
