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| Sesamothamnus leistneri P.Craven ex Swanepoel & A.E.van Wyk, in Swanepoel et E. van Wyk, 2023. |
Abstract
Sesamothamnus leistneri is formally described as a new species with a restricted range, only known from the mountains along the Kunene River in the Kaokoveld Centre of Endemism, a biogeographical region that spans southwestern Angola and northwestern Namibia. The designations “S. leistner(i)anus” or “S. leistneri” have been previously used to refer to this species, but they were not validly published until now. These trees grow in rocky places on mountain slopes, in kloofs (gorges) and on plateaus. Diagnostic characters for S. leistneri include the pronounced tree habit with thickset semi-succulent stem and branches, relatively large green leaves, the corolla lacking a spur, and flowers with a white to cream-white corolla limb. A comparison of some of the more prominent morphological features to differentiate between S. leistneri and its possibly closest relative, S. rivae, as well as the other four species, S. benguellensis, S. guerichii, S. lugardii, and S. busseanus are provided. Based on IUCN Red List categories and criteria, a conservation assessment of Least Concern (LC) is recommended for S. leistneri.
Keywords: Eudicots, endemism, flora, Iona National Park, Kaokoveld Centre of Endemism, Kunene Region, Sesamothamneae, sphingophily, taxonomy
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Sesamothamnus leistneri, fruit morphology. A. Two almost mature fruit and a dehisced one. B. Old dehisced fruit persist for some time on trees. Photographs by W. Swanepoel (A) and A.E. van Wyk (B). Sesamothamnus leistneri, flower morphology. A. Inflorescence showing one open flower, several flowers in different stages of development, and persistent styles (whitish, tipping blackish ovaries) of faded flowers following shedding of the corolla. B. Flowers, open and in bud; note both stamens and stigma positioned in mouth of the corolla tube, also the lack of a spur at the base of the tube. C. Flower showing style with bilobed stigma exserted about 10 mm from the mouth of the corolla tube. D. Distal part of corolla tube opened out to show the yellow inner surface of the tube, white filaments, and anthers positioned at the level of the corolla mouth. Photographs by W. Swanepoel (A, B, D) and A.E. van Wyk (C). |
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| Sesamothamnus leistneri, vegetative morphology. A. Single-stemmed tree showing ± fluted trunk. B. Bark peeling in papery pieces. C. Long shoot with leaves clustered on lateral short shoots. D. Mature leaves showing green colour and ± glossy upper surface. E. Long shoot with spines derived from petioles; one dried leaf blade still attached. Photographs by A.E. van Wyk (A, E) and W. Swanepoel (B–D). |
Sesamothamnus leistneri P.Craven ex Swanepoel & A.E.van Wyk, sp. nov.
Diagnosis:—Single or usually multi-stemmed succulent tree, morphologically most similar to Sesamothamnus rivae, differing by being up to 8 m tall with high succulence of main stems (vs. small multi-stemmed tree up to 3 m tall, low succulence of main stems), flowers lacking a spur (vs. spur present), and flowering during the rainy season with developed leaves (vs. flowering before onset of rainy season when plants still leafless).
Etymology:—The specific epithet honours Otto Albrecht Leistner, who, together with Bernard de Winter, first collected Sesamothamnus leistneri in 1957 during an epic collecting trip to the Kaokoveld (Leistner 2022). In our choice of name, we have chosen to use the epithet as a noun in the genitive case (“leistneri”) rather than an adjective (“leistnerianus”). Either of these options have been used to designate the taxon in the past. We consider the genitive case to be more appropriate, as it indicates that this species is Leistner’s particular discovery, not anybody else’s
Wessel Swanepoel and Abraham E. van Wyk. 2023. A New Species of Sesamothamnus (Pedaliaceae) from Namibia and Angola. Phytotaxa. 626(3); 145-158. DOI: 10.11646/phytotaxa.626.3.1
