Maerua sebrabergensis Swanepoel, 2015

Swanepoel, W., 2015, Maerua sebrabergensis (Capparaceae), a new species from Namibia, Phytotaxa 207 (1), pp. 123-128 : 123-128

Maerua sebrabergensis Swanepoel , sp. nov. ( Figs. 1 & 2 )

A geoxylic suffrutex ± 1 m tall (rarely up to 2 m tall) related to M. parvifolia , from which it differs in having branches that are not rigid (vs. rigid), not spinescent (vs. spinescent), with dark brown, reddish brown or grey bark (vs. white or grey bark), the leaves alternate (vs. alternate or fasciculate), the lamina usually larger, 8–110 × 3–55 mm (vs. smaller, 4–30 × 1–15 mm), narrowly obovate, oblanceolate, obcordate or elliptic (vs. obovate-oblong or oblong-elliptic), glabrous (vs. pubescent, papillose), the inflorescences few-flowered corymbose racemes (vs. flowers solitary or paired), the floral disc margin entire, sinuate or with concavities opposite petal bases (vs. entire or denticulate), the sepals and petals consistently 4 (vs. sepals 3–5, petals 0–4), stamens 46–66 (vs. 15–21) per flower, the ovary cylindrical (vs. ellipsoid), the fruit cylindrical, slightly torulose (vs. cylindrical, torulose or moniliform).

Type:— NAMIBIA. Kunene Region: Zebra Mountains, 4 km northwest of Okaoraore , 1713 BC, 1320 m, 30 September 2012, Swanepoel 320 (holotype WIND!; isotype PRE!) .

Woody subshrub with ascending shoots from underground runners (geoxylic suffrutex), ± 1 m tall, rarely a small tree up to 2 m tall. Trunk of ramets single, short, up to 30 cm long, 80–120 mm in diam., usually buried; stems 10–50 mm in diam. Bark on trunk smooth, khaki-coloured with reddish brown markings or dark to reddish brown; stems dark to reddish brown with numerous, small, whitish lenticels. Branches few, slender, not rigid, glabrous, dark to reddish brown or grey, with whitish lenticels, youngest khaki-green. Leaves simple, petiolate, alternate, glabrous, green; lamina narrowly obovate, elliptic, oblanceolate, or obcordate, (8–)25–70(–110) × (3–)15–40(–55) mm (difference in size not related to position on shoot), coriaceous, apex obtuse, truncate or emarginate, mucronulate, margin entire, base cuneate; midrib conspicuous abaxially, prominently raised especially abaxially, cream-yellow, lateral veins prominent, especially adaxially; petiole short, 2–6 mm long, channelled, cream-yellow, glabrous. Inflorescences few-flowered corymbose racemes, borne terminally or along stems; bracts leaf-like, early caducuous, linear-oblanceolate, somewhat cucullate, green, glabrous or with short papillate hairs. Flowers pedicellate; pedicel glabrous or with short papillate hairs, 4–6 mm long. Receptacle cylindric-infundibular, slender, 7–9 mm long, 2–3 mm wide at mouth, sometimes slightly flattened, slightly ribbed, glabrous or with short papillate hairs; disc not or scarcely produced, margin sinuate, entire or entire with concavities at base of petals. Sepals 4, elliptic, spreading, 8–11 × 4–5 mm, apex acute, navicular, mucronulate, green, glabrous or with short papillate hairs, margin woolly. Petals 4, obovate, clawed, apex acute or rounded, green, margin irregular towards apex, glabrous. Androphore extending to 0.5–2.0 mm beyond receptacle, 3.9–6.2 mm long. Stamens 46–66; filaments up to 13 mm long, white; anthers oblong, basifixed, 1.1–1.5 × 0.4–0.6 mm long. Gynophore 12.3–13.8 mm long, yellowish green. Ovary cylindrical, 1-chambered, 2.8–3.9 mm long, 0.9–1.1 mm diam., pale green; placentas 2, ovules 6–9 on each; stigma capitate, dark brown. Fruit narrowly cylindrical, slightly torulose, 16–45 mm long, 4–6 mm diam., faintly colliculate, glabrous, green to maroon-green when fully developed. Seeds not seen.

Phenology:— Flowers were recorded in September and October.

Distribution and habitat:— At present M. sebrabergensis is only known from one valley in the botanically poorly explored Zebra Mountains, south of the Kunene River in northwestern Namibia ( Fig. 3 ) where it is localized and rare. The species may, however, eventually prove to be more widespread in the Zebra Mountains as suitable habitat is not limited to the specific valley where it was found. Maerua sebrabergensis grows on heavy black clay (“cotton”) soil derived from weathered anorthosite of the Kunene Complex ( Miller & Schalk 1980, Mendelsohn et al. 2002). It occurs on a valley floor in Colophospermum-Acacia woodland in the upper part of the southern Zebra Mountains at elevations of 1310–1330 m, 195 km from the Atlantic Ocean. Average annual rainfall in the area is 250–300 mm ( Mendelsohn et al. 2002).

Conservation status:— Maerua sebrabergensis is rare and localised with only 16 plants (clones) known from an uninhabited part of the Zebra Mountains. It should be considered as Critically Endangered (CR D) due to the small population size ( IUCN 2012).

Etymology:— The specific epithet refers to the “Sebraberge” (Afrikaans for “Zebra Mountains”) in the Kaokoveld of northwestern Namibia, the type locality of the new species.

Notes:— Maerua sebrabergensis differs from M. parvifolia in habit as well as in leaf, flower and fruit characters. Plants of M. sebrabergensis in southern Africa are markedly different from M. parvifolia in being woody subshrubs with ascending shoots (ramets) from underground runners, ± 1 m tall, the ramets rarely developing into small trees up to 2 m tall with branches and branchlets slender and not rigid. Maerua parvifolia in southern Africa is a spreading, virgate shrub with slender rigid branches and the branchlets are often abbreviated and spinescent. In tropical Africa, however, M. parvifolia has also been described as a suffrutex with many ascending shoots from underground runners ( Uganda, Kenya and Tanzania). Some of the more prominent morphological features to differentiate M. sebrabergensis and M. parvifolia are compared in Table 1. Diagnostic features for M. sebrabergensis were determined through examination of fresh material and for M. parvifolia from both fresh and herbarium material and the literature ( Wild 1960, Elffers et al. 1964, Killick 1969, 1970).

Maerua sebrabergensis can be confused with M. juncea Pax (1891: 302) subsp. juncea due to similarities in the fruit, especially in the Kaokoveld where it is often narrower than is typical for the subspecies (8–10 mm diam. instead of ± 20 mm diam.). The fruit in M. sebrabergensis , however, is even narrower (4–6 mm diam.) and the young branches is grey, dark or reddish brown with whitish lenticels instead of green and striated as in M. juncea .

Figures

FIGURE 1. M. sebrabergensis in its natural habitat. A, clonal growth with several ramets in foreground, showing ascending shoots, ± 0.7 m tall; trees in background are Acacia kirkii Oliver (1871: 350). B, suffrutex showing flood-exposed runner. Photographs: W. Swanepoel.

FIGURE 2. M. sebrabergensis. A, flower; B, receptacle and disc; C, disc; D, fruit; E, leaves. Scale bar 3 mm (A–C) or 10 mm (D, E). All from Swanepoel 320. Artist: Daleen Roodt.

FIGURE 3. Known distribution of M. sebrabergensis.