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| Petalidium sesfonteinense Swanepoel & E.Tripp, in Swanepoel & Manzitto-Tripp, 2022. |
Abstract
Petalidium sesfonteinense, previously most commonly confused with the widespread P. variabile, is here described as a new species. It is only known from the Sesfontein area in the Kaokoveld Centre of Endemism, northwestern Namibia, where it grows on hillsides and along ephemeral riverbeds. Diagnostic characters for P. sesfonteinense include the short, stout trunk on older plants, white bark that peels on the younger branches in long, narrow strips, dendritic trichomes on vegetative parts, flowers in short dichasia with acute oblanceolate bracts, flowers with externally glabrous corollas, corolla lobes that are pink, magenta, apricot or cream and with the two upper lobes connate towards the base and the lower lobe with two yellow spots near the base. A comparison of some of the more prominent morphological features to differentiate Petalidium sesfonteinense from close relatives is provided. Based on IUCN Red List categories and criteria, a conservation assessment of Least Concern (LC) is recommended for the new species.
Keywords: Desert, endemism, flora, Kaokoveld, Ruellieae, Sesfontein, taxonomy
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| Petalidium sesfonteinense Swanepoel & E.Tripp. Morphology of flowers. A–D. Flowers in front view showing variation in corolla colour and lobe margins, with two yellow nectar guides. E. Corolla in lateral view. F. Corolla in dorsal view. G. Corolla in ventral view. Scale bar = 5 mm. Photographs: W. Swanepoel. Swanepoel 568 (E, F & G). |
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| Petalidium sesfonteinense Swanepoel & E.Tripp. A. Habit. Plant about 40 cm tall. B. Flower, shoots, and leaves; greyish leaves are still densely covered in trichomes; green leaves almost glabrous. Photographs: W. Swanepoel. Swanepoel 568. |
Petalidium sesfonteinense Swanepoel & E.Tripp, sp. nov.
Diagnosis:— A woody shrub up to 1 m tall, morphologically most similar to Petalidium kaokoense and P. variabile; from P. kaokoense it differs in having an indumentum on vegetative parts of relatively slender dendritic trichomes (vs. relatively stout stalked-stellate trichomes interspersed with dendritic trichomes), bracts oblanceolate (vs. linear-oblanceolate or linear-lanceolate), bracteoles symmetrically elliptic or narrowly ovate with long multicellular glandular trichomes and venation weak or not prominent (vs. asymmetrically elliptic-oblong, long multicellular glandular trichomes absent, reticulation prominent), corolla with expanded portion of tube glabrous externally (vs. strigose), upper lobes connate for 20–30% of their length and obovate (vs. 50%, oblong), lobes variously coloured (white, pink, magenta, apricot, yellow, or cream) and in contrast with maroon throat and mouth (vs. lobes, throat, and mouth maroon), seeds cordate (vs. discoid or ovate); from P. variabile it differs in indumentum on young stems different from that on leaves (vs. similar), indumentum on leaves dendritic (vs. strigose), bracteoles usually with long multicellular trichomes (vs. absent), expanded portion of corolla tube glabrous externally (vs. with short appressed simple trichomes), all corolla lobes of same colour and shade (vs. front corolla lobe differently coloured or shaded than other lobes), capsule flattened ellipsoid or ovoid, sides rugose or smooth (vs. flattened ovoid, sides smooth).
Distribution and habitat:—At present, Petalidium sesfonteinense is only known from the vicinity of Sesfontein and the surrounding mountainous area up to Tomakas in the west and Warmquelle in the east (Fig. 3). It occurs on hillsides, along seasonally dry riverbeds and at the base of rocky outcrops at elevations of 340–1070 m a.s.l., about 75–125 km from the Atlantic Ocean. Average annual rainfall in the area is 100–150 mm (Mendelsohn et al. 2002).
Conservation status:—Petalidium sesfonteinense is locally common and probably more widespread in suitable habitats than currently recorded. It is here considered not in immediate conservation danger, because it occurs in sparsely to unpopulated areas and does not seem to be utilised by humans. However, it is browsed by livestock (goats) of the local inhabitants (pers. obs.). The area of occupancy is estimated at < 20000 km² (2250 km²) with less than 10 (8) subpopulations. However, since no decline in population size or numbers is known, it is here ranked as Least Concern (LC) (IUCN 2012).
Etymology:—The specific epithet refers to Sesfontein, a village in northwestern Namibia near the type locality.
Wessel Swanepoel and Erin A. Manzitto-Tripp. 2022. Petalidium sesfonteinense (Acanthaceae), A New Species from the Kaokoveld, Namibia. Phytotaxa. 549(2); 127-135. DOI: 10.11646/phytotaxa.549.2.1
