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Petalidium ovatum (Schinz) Clarke, P. englerianum (Schinz) Clarke in Swanepoel, Dexter, Loiseau et van Wyk, 2023. |
Abstract
The name Petalidium ovatum is reinstated and an amplified description is provided for a species of Petalidium confined to Namibia. Petalidium ovatum used to be treated as a synonym of the widespread P. englerianum, but morphological characters support the reinstatement. Petalidium ovatum is a range-restricted species, only known from the Khorixas-Bergsig area in the Kaokoveld Centre of Endemism, northwestern Namibia, where it grows on arid hillsides and along ephemeral riverbeds and drainage lines. Diagnostic characters for P. ovatum include the pale grey, often almost white, appearance of the plants, vegetative parts with a dense white indumentum of both stellate and dendritic trichomes, flowers borne in short few-flowered dichasia, bracts oblanceolate with apices acute or obtuse, and bracteoles widely ovate. The flowers of P. ovatum are distinctive in having the anterior corolla lobe partly or completely yellow, the others burgundy, and with the two upper lobes connate towards the base for almost half their length. A comparison of some of the more prominent morphological features to differentiate Petalidium ovatum from P. englerianum, its morphologically most similar relative, is provided. Based on IUCN Red List categories and criteria, a conservation assessment of Least Concern (LC) is recommended for the reinstated species.
Eudicots, desert, endemism, Flora, Kaokoveld, Kaokoveld Centre of Endemism, Kunene Region, Ruellieae, Khorixas, Bergsig, lectotypification, taxonomy
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Petalidium ovatum, habit. A. Dwarf shrub, ca. 350 mm high (at Farm Fonteine 717). B. Base of mature plant showing woody stems with fissured greyish white bark (at Farm Fonteine 717). Petalidium ovatum, habitat and habit. A. Plant (ca. 600 mm high) on arid hillside at Grootberg, highest point on road C39 between Vrede and Bergsig. B. Plant (ca. 500 mm high) in ephemeral riverbed, Farm Inhoek 482, 8 km from Khorixas on road C39. Photographs: W. Swanepoel. |
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Petalidium ovatum, leaf (A) and flower morphology (B–E). A. Branchlet with leaves and flowers. B. Flower in front view. C. Flower in lateral view; note widely ovate bracteole with venation ca. visible. D. Flower in front view. E. Flower in lateral view; note bracteoles with indumentum particularly dense and venation not visible. Petalidium englerianum, leaf (A) and flower morphology (B–E). A. Branchlet with leaves and flower, the latter starting to fade. B. Flower in front view. C. Flower in lateral view. D. Flower in front view. E. Relatively old flower; upper corolla lobes having turned brownish orange as they are fading. Photographs: W. Swanepoel. |
Petalidium ovatum (Schinz) Clarke (1899: 90)
Wessel Swanepoel, Kyle G. Dexter, Oriane Loiseau and Abraham E. van Wyk. 2023. Reinstatement of the Name Petalidium ovatum (Acanthaceae), with an amplified description of the species. Phytotaxa. 626(3); 159-169. DOI: 10.11646/phytotaxa.626.3.2
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