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| Petalidium etendekaense Swanepoel, E.Tripp & A.E.van Wyk, in Swanepoel, Manzitto-Tripp, Dexter et van Wyk, 2024. Photographs by W. Swanepoel. |
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).
Keywords: desert, endemism, flora, Kaokoveld, lectotypification, Ruellieae, Bergsig, taxonomy
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| Petalidium etendekaense. Morphology of flowers and leaves. A, B, C, D. Flowers in front view, each from a different plant to show variation; note all corolla lobes of a flower being similarly coloured. E. Flower and bracteole in lateral view; note absence of long, simple trichomes on bracteoles. F. Flower with bracteoles, viewed from below. G. Shoot showing leaves with dense white indumentum and persistent bracteoles of spent flowers, some enclosing developing fruit. Scale bar = 3 mm. Photographs by W. Swanepoel. |
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| Petalidium etendekaense. Habitat and habit. A. Several plants (foreground and greyish dwarf shrubs in the background) growing on the gently sloping ground between rocky hills in stony soil derived from Etendeka Group basalt. B. Mature plant (ca. 600 mm high) with very short main stem and greyish appearance. Photographs by W. Swanepoel. |
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| Petalidium etendekaense. Habitat and habit. A. Plant (ca. 350 mm high) with relatively long single main stem, growing among rocks of Etendeka Group basalt. B. Part of fissured greyish white bark on woody stem (ca. 60 mm in diam.) at base of mature plant. C. Plants growing in abundance (right front and low greyish shrublets in background) among rocks of Etendeka Group basalt on a hill slope. Photographs by W. Swanepoel. |
Petalidium etendekaense Swanepoel, E.Tripp & A.E.van Wyk, sp. nov.
Diagnosis:—A woody shrub up to 1 m tall, morphologically most similar to Petalidium glutinosum and P. variabile, but differing from both in having indumentum on leaves tomentose-strigulose (vs. strigulose); corolla lobes ascending-spreading with respect to the corolla tube axis (vs. patent or upper lobes in line with tube to sub-patent), lobes all similarly coloured (vs. anterior and sometimes lateral lobes differently coloured or shaded than upper lobes); differing from P. glutinosum in absence of long, simple trichomes on bracteoles abaxially; differing from P. variabile in absence of short geniculate simple trichomes on bracteoles abaxially.
Etymology:—The specific epithet “etendekaense” refers to the Etendeka Tableland landscape (or plateau), which
was formed by lava flows (basalts of the Etendeka Group) ca. 132 million years ago due to sea floor spreading and the
formation of the South Atlantic. This plateau is a component of a significant igneous province, and its counterpart in
Brazil is represented by the Paraná basalts (Goudie & Viles 2015). The name “Etendeka” is derived from the Otjiherero
word for layered or stacked, in reference to the flat-topped mountains that define the landscape (Detay & Detay 2017,
Atlas of Namibia Team 2022). The entire known population of Petalidium etendekaense is located in this landscape,
growing on soils derived from Etendeka basalt.
Wessel Swanepoel, Erin A. Manzitto-Tripp, Kyle G. Dexter and Abraham E. van Wyk. 2024. Petalidium etendekaense (Acanthaceae), A New Species from Namibia, with Notes on the Taxonomic Identity of P. glutinosum. Phytotaxa. 636(1); 35-47. DOI: 10.11646/phytotaxa.636.1.3
