Commiphora benguelensis Swanepoel, 2015

Swanepoel, W., 2015, Commiphora benguelensis (Burseraceae), a new species from Angola, Phytotaxa 217 (2), pp. 191-196 : 191-193

Commiphora benguelensis Swanepoel , sp. nov. ( Fig. 1 )

Differs from C. africana in being dioecious or monoecious (vs. dioecious); spineless (vs. spinescent); exudate glutinous, white (vs. not glutinous, clear); leaves trifoliolate, usually with few simple ones also present (vs. invariably trifoliolate), leaflets pilose adaxially, tomentose abaxially (vs. pilose to tomentose (in southern Africa), similar on both sides); flowers sessile (vs. pedicellate); disc not grooved on inside, lobes bifid (vs. disc grooved on inside, lobes simple); fruit with exocarp pilose (vs. glabrous); pseudo-aril yellow, with two short lobes and two long commissural arms (vs. red with 4 arms of variable size and form, or pseudo-aril almost completely covers the putamen).

Type: — ANGOLA. Namibe Province: 22 km SSE of Chapeu Armado in maritime hills, 1412 CB, 438 m, 16 April 2010, Swanepoel 324 (holotype PRU!; isotype LUBA!) .

Dioecious or monoecious shrub-like tree up to 2.5 m tall, 1–5 m diam. Trunk simple and short, up to 0.3 m long, 0.2 m diam., or branching repeatedly above ground level, appearing succulent. Bark beige, grey or green-grey with black spots in places, on branchlets brown, grey-brown or reddish brown. Branches and branchlets glabrous with few small, prominent lenticels; young growth pilose; dwarf lateral branchlets scarred. Exudate white, viscous, drying to form a soft, pale yellow, translucent resin. Leaves mostly trifoliolate, usually few simple ones also present, clustered on branches and on dwarf lateral branchlets but spirally arranged on actively elongating shoots, petiolate, green, indumentum white; lamina in simple leaves obovate or suborbicular, apex acute or obtuse, base cuneate or obtuse, 4–25 × 4–18 mm; terminal leaflets in trifoliolate leaves subsessile or with petiolule up to 5 mm long, lamina obovate, elliptic, suborbicular or obcordate, apex rounded, truncate or retuse, base cuneate or cuneate-attenuate, 9–35 × 7–24 mm, lamina of lateral leaflets obovate, elliptic or suborbicular, often asymmetric, apex rounded, obtuse or acute, base cuneate, rounded, obtuse or truncate, 4–18 × 3–13 mm; simple and trifoliolate leaves with margins coarsely crenate-serrate or dentate-serrate in distal half, crenate or dentate towards apex, entire towards base, often revolute, lamina densely pilose adaxially, tomentose abaxially, with scattered, short glandular hairs on both sides, midrib and lateral veins prominent and conspicuous on both sides, petiole densely pilose with short glandular hairs, grooved adaxially, 3–24 mm long, pentagonal in transverse section with 5 vascular bundles, sectional dimensions 0.8–1.0 × 0.8–1.2 mm. Inflorescence s: flowers axillary, solitary or clustered. Flowers precocious, unisexual, hypogynous, sessile. Bracts ovate or semi-circular, 0.3–0.6 mm long, densely pilose abaxially. Calyx pale green, densely pilose abaxially, glabrous adaxially or with few scattered hairs, lobes triangular, acute. Petals elliptic, broadly lanceolate or broadly oblanceolate, cream-coloured, pilose abaxially, glabrous or sparsely hairy towards apex adaxially, finely ciliate. Disc cylindrical with 4 distinct lobes, bifid at apex, not adnate to perianth. Male flowers 1.8–2.5 mm long, calyx 0.9–1.1 mm long, calyx lobes ± 0.6 mm long, petals 1.8–2.7 × 0.9–1.1 mm, spreading-ascending, minute tip inflexed; disc fleshy; stamens 8, filaments filiform, 4 long stamens with filaments 1.0– 1.4 mm long, inserted on outer margin of disc lobes, 4 short stamens with filaments 0.6–0.9 mm long, inserted between lobes on outer margin of disc, anthers 0.7–0.9 mm long, all equal; gynoecium rudimentary, ± 0.5 × 0.2 mm. Female flowers 2–3 mm long, calyx 0.9–1.5 mm long, calyx lobes 0.6–0.8 mm long, petals 2.1–2.4 × 0.9–1.1 mm, ascending-spreading; staminodes 8, alternately long and short, inserted on disc margin; ovary half-inferior, style relatively short, ovary and style densely pilose, stigma obscurely 4-lobed; pistil with stigma below top of flower (equal with calyx lobes), 1.2–1.5 × 0.9–1.1 mm. Fruit a drupe, subglobose or obovoid, slightly flattened, suture rectilinear, 6.8–8.8 × 7.4–8.4 × 6.2–7.1 mm; pericarp 2-valved; exocarp densely pilose, cherry-red when ripe; mesocarp not very fleshy; putamen flattened, asymmetrical, rugose, subglobose or ellipsoid with one fertile and one sterile locule; ± 7.0 × 5.5 × 3.5 mm; fertile locule ± semi-circular in apical view; sterile locule slightly convex in apical view; suture rectilinear; angle between locules at apex ± 60°; pseudo-aril yellow, cupular, covering ± 30% of putamen, with short convex facial lobe on fertile locule and triangular lobe on sterile locule, commissural arms broad, almost reaching apical pits, part of pseudo-aril on fertile locule narrow, broad on sterile locule; apical pits small.

Phenology: — Commiphora benguelensis flowers in November and December. Fruits were encountered on plants in December.

Distribution and habitat: — Commiphora benguelensis is presently known from various localities in the coastal zone of southwestern Angola, from Namibe to ± 40 km inland and northwards to Santa Maria ( Fig. 2 ). This arid area falls within the Kaokoveld Centre of Plant Endemism ( Van Wyk and Smith, 2001) and is part of the Namib Desert. C. benguelensis is uncommon and occurs with several other species of Commiphora on mountain slopes and level areas, in arid bushveld and desert shrubland at elevations of 50– 600 m.

Conservation status: — Commiphora benguelensis is not under any threat as the plants are located in remote, sparsely populated areas.

Etymology: —The specific epithet refers to the Benguela Current of the Atlantic Ocean which plays a major role in maintaining the arid climatic conditions of the bordering Namib Desert and the Kaokoveld Centre ( Seely 2004). The Benguela Province, one of the two politically demarcated provinces of Angola in which the new species occurs, is also named after the Benguela Current.

Notes: — Commiphora benguelensis can be confused with C. africana , with which it shares a similar habit and non-peeling bark (at least where the two taxa are sympatric), pilose young branches, hairy, trifoliolate leaves and hypogynous flowers. Commiphora benguelensis differs from C. africana in several characters of the habit, exudate, leaves, flowers, and fruit.

Some of the more prominent morphological features to differentiate C. benguelensis from C. africana are compared in Table 1.

Figures

FIGURE 1. Commiphora benguelensis. Flowers, seed and leaves. (A–D) Male flower; (B) with calyx and corolla partly removed, showing stamens; (C) disc as seen from the inside (schematic); (D) disc as seen from above (schematic). (E–H) Female flower; (F) with calyx and corolla partly removed, showing pistil and rudimentary stamens; (G) disc as seen from the inside (schematic); (H) disc as seen from above (schematic). (I–L) Putamen with cupular pseudo-aril; (I) sterile locule; (J) fertile locule; (K) sutural view, fertile locule left, sterile locule right; (L) apical view. (M & N) Leaves; (M) branch with trifoliolate and simple leaves; (N) branch with trifoliate leaves only. Scale bars (A & B) 1 mm, (E & F) 1 mm, (I–L) 1 mm, (M & N) 10 mm.Artist: Daleen Roodt. Vouchers: leaves from Swanepoel 324, female flowers and seed from Swanepoel 328, male flowers from Swanepoel 329.

FIGURE 2. Known distribution of Commiphora benguelensis.