Euphorbia rimireptans Swanepoel, R. W. Becker & Alma Moller 2019, sp. nov.
Creators: name: Swanepoel, Wessel
name: Becker, Rolf W.
name: Mӧller, Alma
name: Cauwer, Vera De
Publisher: name: Zenodo
Year: 2019
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Malpighiales
Euphorbiaceae
Euphorbia
Euphorbia rimireptans

description: Euphorbia rimireptans Swanepoel, R.W.Becker & Alma Möller sp. nov. (Figs.1 to 4)   
 Diagnosis: —Succulent shrublet up to 0.5 m in its greatest diam., similar to E. giessii, from which it differs in being procumbent, sometimes pendant (vs. erect, up to 0.8 m high); branches, shorter and thinner (up to 0.5 m long, 2.8–6.0 mm diam.), soft, rubber-like, terete or only slightly tapering [vs. longer and thicker (up to 0.8 m long, 4–12 mm diam.), rigid, firm, tapering]; leaf lamina not panduriform, of uniform thickness, glabrous (vs. somewhat panduriform, thickened towards apex, densely hairy at base adaxially); bracts dissimilar to the leaves, hairy adaxially at base only, otherwise glabrous (vs. bracts similar to the leaves, hairy adaxially); gland shape mostly variable on each involucre, oblong, oblong-elliptic, elliptic, reniform, ovate or flabellate (vs. gland shape uniform on each involucre, oblong-elliptic, elliptic or sub-circular); staminate flowers with filaments glabrous, shorter (0.4–0.8 mm long), anther theca pale yellow [vs. filaments glabrous or with long hairs, longer (0.9–1.2 mm long), anther theca pale green]; capsule glabrous or sparsely hairy, rarely dotted, pedicel ± 0.6 mm diam. (vs. sparsely to densely hairy, seldom glabrous, conspicuously dotted, pedicel ± 1.1 mm diam.); seed verrucose.   
 Type: — NAMIBIA. Kunene Region: Skeleton Coast National Park, 198 m high koppie, 200 m west of track between Okau Fountain and Sarusas Mine, 20.5 km east of Cape Fria, northern side, facing west, below peak, 1812 AC, 190 m, 21 February 2019, Swanepoel & Becker 358 (holotype WIND!; isotypes PRE!, PRU!).   
 Succulent, unarmed, dioecious shrublet, branching from a grey-coloured base, procumbent, sometimes pendant, up to 0.5 m in greatest diam., with subtuberous, fleshy main root. Branches ± radiate, irregularly curved or ± straight, often all orientated in same direction from base, frequently intertwined, branchlets opposite and decussate or opposite and distichous, often lacking on side facing ground, branches and branchlets terete or slightly tapering, often few curved, articulated at base, indistinctly constricted at nodes, glabrous, glaucous on recent growth, different shades of green, yellow, orange, brown or maroon, sometimes glossy, inconspicuously minutely white-dotted, up to 0.5 m long, 2.8–6.0 mm diam. Leaves caducous, leaving a prominent crescentic brown scar, petiole 0.5–0.7 mm long, 0.7 mm diam., white sericeous adaxially, lamina fleshy, flat or conduplicate, spreading, green or when drying, orange to red, glabrous, lanceolate, elliptic, ovate or obovate, 2.1–3.2 × 1.8–2.5 mm, apex acute or obtuse, often dorsally apiculate, margin entire or sparingly denticulate, sometimes whitish pellucid. Inflorescences terminal dichasial cymes, bearing 2 or 3 cyathia, usually several times forked, cyme branches slightly decreasing in diam. as forking develops, usually erect or sub-erect facing away from ground, 1.3–30.0 mm long, l.6– 2.6 mm diam. Bracts petiolate with apical part ovate-acute or suborbicular, thickened towards apex, sub-conduplicate, dorsally apiculate, appearing ± panduriform, clasping involucre, erect or apical part sub-erect, sericeous adaxially at base, margin entire, crenulate or denticulate towards apex, in staminate cyathia 1.4–2.0 × 1.5–2.2 mm including petiole, smaller in pistillate cyathia, 1.2–1.5 × 0.9–1.4 mm including petiole. Involucre pale green to yellow-green, often maroon in places, glabrous outside except for strips of very short, whitish pellucid hairs opposite margins of bract bases, white hairy inside, partitions marked with longer hairs, particularly dense tuft at apex just below gland; involucres in staminate plants cupuliform, 2.1–2.7 mm long, 1.9–2.7 mm diam. including glands, pistil rudimentary, 1.6–2.3 mm long; involucres in pistillate plants obconical, smaller, 1.9–2.1 mm long, 1.6–1.8 mm diam. including glands, rudimentary anthers up to 0.2 mm long; glands 5, green, yellow-green or bright orange-yellow, often becoming orange or dark brown when becoming dry, shape variable even on a single involucre: transversely oblong, oblong-elliptic, elliptic, reniform, ovate or flabellate, semi-erect to spreading, transversely slightly concave adaxially, margins entire or with few irregular crenations, in staminate plants ± contiguous, 0.8–1.5 × 0.6–0.8 mm, in pistillate plants ± contiguous, later separate, smaller, 0.6–1.0 × 0.3–0.5 mm, nectar transparent, not forming globules; lobes 5, ± quadrate or somewhat flabellate, apex irregularly ciliate-fimbriate sometimes bi-lobed, densely sericous inside, glabrous outside, ± 0.5 × 0.5 mm. Staminate flowers ± 25, glabrous, well exerted from involucre with simple or branched plumose bracteoles 1.6–1.9 mm long; pedicels filiform, whitish, when fully developed 2.3–2.6 mm long; filaments terete or slightly tapering, pale green, 0.4–0.8 mm long; anther thecae pale yellow; pollen yellow. Pistillate flowers erect, included in involucre, glabrous; pedicels short, ± 0.5 mm long, 0.3 mm diam., subtended by plumose bracteoles similar to those in staminate plants but smaller, ± 1.2 mm long; ovary ovoid, glabrous or rarely with few slightly crisped, weak hairs, green, 0.7–0.9 mm long, 0.7–0.9 mm diam.; ovule ovoid, more or less filling the cell, ± 0.3 × 0.2 mm diam., suspended under obturator, margin irregularly denticulate; styles 3, united in a stout column for a third to half their length, sub-erect to ascending spreading, 0.7–1.2 mm long, apices shortly bifid, widely divergent, spreading, recurved. Capsule (2)3-locular, obtusely (2)3-lobed ovoid, apex and base slightly emarginate, green or in places maroon, rarely dotted, glabrous or rarely with few slightly crisped, weak hairs, 3.5–3.9 × 3.2–4.2 mm, held erect, exserted from involucre but base sometimes within, pedicel green or maroon, 1.2–1.4 long, 0.6–0.8 mm diam.; seed ± ovoid, obscurely 4-angled, apex sub-acute, base ± truncate, ashy or ashy-brown, obtusely rugose, verrucose, 2.2–2.5 × 1.5–1.6 × 1.3–1.6 mm.   
 Phenology: —Cyathia were recorded from February to July.   
 Distribution and habitat: — At present Euphorbia rimireptans is known from several localities in the Skeleton Coast National Park, Namibia, to the east and southeast of Cape Fria, all within a radius of 19 km (Fig. 5). This part of the Skeleton Coast National Park falls within the Namib Desert zone of the Kaokoveld Centre of Endemism, a biogeographical region known for its many restricted-range plants and animals, and extending from northwestern Namibia to southwestern Angola (Van Wyk & Smith 2001). Euphorbia rimireptans occurs 5–23 km from the coast at elevations of 60–225 m a.s.l. Average annual rainfall in the area is less than 50 mm, occurs in summer, and is highly erratic. The area also regularly receives fog from the ocean (Mendelsohn et al. 2002). The new species occurs in small, isolated colonies of about twenty plants each, occupying a very specific habitat. It is found on low ridges and outcrops of latite of the Sechomib and Sarusas Formations of the Etendeka Group of the Karoo Super Group (Guj et al. 2011), in areas of broken rock. Here it grows in fully exposed conditions in sand-filled rock fissures on level and low, ± vertical areas. Conditions in this habitat are extremely harsh, with low rainfall, high temperatures and strong winds [calm for only 14% of the time as measured at Möwe Bay to the south (Mendelsohn et al. 2002)]. In addition, plants have to withstand the abrasive effect of windblown sand. This is particularly evident in those growing on level areas and not being protected by surrounding rocks, which have glossy branches, a feature also observed in other plant species occupying the same habitat.   
 Conservation status: — Although rare and known from a relatively small area, Euphorbia rimireptans is probably not threatened at present, as it occurs in the Skeleton Coast National Park, a protected area. No signs of damage caused by animals or humans could be found on any of the in situ specimens examined. It should be considered as Vulnerable (VU D) due to the small known population size (IUCN 2012).   
 Etymology: —The specific epithet is derived from Latin and refers to the habit of Euphorbia rimireptans: ‘ rimireptans’ = creeping from rock fissures.   
 Notes: —The nearest relative of E. rimireptans appears to be E. giessii (Fig. 6), a species from which it differs in habit, leaf, flower, and fruit characters. Euphorbia rimireptans occurs in the northern parts of the Skeleton Coast National Park in the vicinity of Cape Fria, between the Nadas and Khumib rivers, and E. giessii extends from the Engo River Valley south to the Ugab River, and beyond the Park boundaries to the Kuiseb River. The locality of E. rimireptans in the Nadas River Valley is only 4.8 km to the southwest of the closest known locality of E. giessii. Thus, based on the observations to date, it appears as if their distribution ranges could overlap. Interestingly, throughout the known ranges, except for one locality, E. rimireptans seems to occur to the west of E. giessii. Further fieldwork is needed to determine the exact ranges with more accuracy. Some of the more prominent morphological features to distinguish between the two species are provided in Table 1.   
 Euphorbia negromontana, from the coastal Namib in southwestern Angola, shares the presence of plumose bracteoles in the cyathia of pistillate plants with the new species and E. giessii. Euphorbia rimireptans, however, can be distinguished from E. negromontana by its procumbent or pendant habit (vs. pulvinate), branchlets of the inflorescences that are not particularly fragile (vs. fragile), and by its larger (3.5–3.9 × 3.2–4.2 mm) ovoid capsule, which is glabrous or rarely with a few crisped, weak hairs (vs. smaller, ± 2 mm diam., subglobose, pubescent) (Leach 1970).   
 On the label of the specimen Müller & Loutit 2166 in WIND, it is indicated as being collected in quarter degree square 1812AD, at the hillocks near the mouth of the Sechomib River. This is incorrect since the mouth of this river is located in 1812CB, thus “1812AD” on the label should read “1812CB”.   
 Additional specimens examined (paratypes): — NAMIBIA. Kunene Region: Skeleton Coast National Park, 198 m high koppie, 200 m west of track between Okau Fountain and Sarusas Mine, 20.5 km east of Cape Fria, northern side below peak, 1812 AC, 190 m, 21 February 2019, Swanepoel & Becker 359 (WIND!); Skeleton Coast National Park, rocky outcrop 50 m east of archeological site, 23 km east of Cape Fria, 1812 AC, 190 m, 21 February 2019, Swanepoel & Becker 360 & 361 (WIND!); Sechomib River, koppies near mouth of river, “ysterklip”, 1812 CB, 24 April 1982, Müller & Loutit 2166 (WIND!); Skeleton Coast National Park, rocky ridge just south of Sechomib Poort, 1 km east of Sechomib Fountain, 1812 CB, 100 m, 21 February 2019, Swanepoel & Becker 363 (WIND!).
description: Published as part of Swanepoel, Wessel, Becker, Rolf W., Mӧller, Alma & Cauwer, Vera De, 2019, Euphorbia rimireptans (Euphorbiaceae, Articulofruticosae), a new species from the Skeleton Coast, Namibia, pp. 165-173 in Phytotaxa 414 (4) on pages 166-171, DOI: 10.11646/phytotaxa.414.4.2, http://zenodo.org/record/13715522