Mezoneuron angolense Welwitsch ex Oliver

Clark, Ruth P., 2016, A Taxonomic Revision of Mezoneuron (Leguminosae: Caesalpinioideae: Caesalpinieae), Phytotaxa 274 (1), pp. 448-450 : 448-450

1. Mezoneuron angolense Welwitsch ex Oliver

Fl. Trop. Afr. 2: 261. 1871.

Type:— ANGOLA, Golungo Alto and Pungo Andongo, Dr Welwitsch s.n.

Lectotype:— ANGOLA, Pungo Andongo, Welwitsch 606 LISU (LISU208797, image!), ( Brenan 1967); isolectotypes LISU (LISU208798, image!), BM (BM000842328!).

Remaining syntype:—Golungo Alto, between Sange and Camilungo, Welwitsch 607 LISU; isosyntypes BM!, K (K000232355!), P (P000374798!) .

Synonym. Caesalpinia angolensis (Welwitsch ex Oliver) Herendeen & Zarucchi. Ann. Missouri Bot. Gard. 77(4): 854. 1990.

Scandent shrub or liana, to 20 m in length. Stems with scattered recurved prickles ca. 8 mm; glabrous or sparsely tomentose. Stipules semi-persistent, triangular, 1–2 × 1–2 mm; glabrous to moderately tomentose, or with hairs only on the margins. Leaves with (2–) 3–11 pairs pinnae; petiole 1.8–6.5 cm; rhachis 5.7–30 cm, with recurved prickles in pairs at the pinna insertion points, and scattered on the internodes, sometimes densely; pinnae ca. 2.5–11 cm long, sometimes with recurved prickles in pairs at the leaflet insertion points, and scattered on the internodes; 4–8 [–9] pairs of leaflets per pinna; leaf rhachis, petiole, and pinna rhachis sparsely to moderately whitish to orange pilose to tomentose. Leaflets opposite or subopposite; the terminal leaflets obovate, base oblique, apex obtuse to retuse, 1.0–2.6 [–3.5] × 0.6–1.5 cm; lateral leaflets broadly oblong, base oblique, apex obtuse to retuse, 0.7–2.2 × 0.4–1.2 cm; upper surface glabrous, or sparsely tomentose, lower surface with long hairs on basal portion of the midvein, or along whole midvein, sometimes on basal part of blade, occasionally sparsely across whole blade; 2˚ veins anastomosing, 3˚ veins reticulate, scarcely visible above, slightly raised or faintly visible below. Inflorescence a raceme or panicle (often few-branched), axillary or terminal, to ca. 50 cm, axes sparsely to moderately orange tomentose, sometimes glabrous on the basal portion; pedicels 5–11 mm, not articulated, sparsely to moderately orange tomentose. Bracts sometimes present, persistent, oblong with acuminate apex, or triangular, 1–2 × 1–2 mm, subglabrous, with few hairs at margins, or sparsely tomentose; bracteoles caducous, lanceolate, sometimes broad in basal portion, tapering to a long-acuminate apex, 3–6 × 1 mm, sparsely to moderately orange tomentose on both surfaces. Flowers with hypanthium 2–4 × 5–10 mm; lower calyx lobe 7–9 × 3–6 mm; other lobes 5–7 × 3–4 mm; inner surface of lobes distinctly striate, outer surface of hypanthium and lobes glabrous to moderately orange tomentose, with margins ciliate. Median petal obovate, sometimes reflexed backwards, laterally inrolled, with a transverse flap of tissue on inner surface between claw and blade, 5–10 × 5–10 mm, claw 1–4 mm, the flap of tissue sparsely hairy, the margins of the blade with a fringe of hairs, and some hairs on the inner surface behind flap of tissue, and at the edges; outer surface glabrous. Upper lateral petals suborbicular to obovate, 6–12 × 5–8 mm, including claw ca. 1 mm long. Lower lateral petals oblong to elliptic, 8–13 × 4–10 mm, including claw 1–2 mm long; all laterals villous on inner surface of claw, and sometimes the basal ⅓ of blade, outer surface glabrous. Stamen filaments 11–17 mm long, densely villous on the basal ½ on inner surface; anthers 1.5–2 mm long. Ovary ca. 5–7 mm long, glabrous, or sparsely, or densely tomentose, sometimes partially or only along upper edge (see discussion); style ca. 10–12 mm long; stigma funnel-shaped, to 2 mm wide, the rim papillate. Fruit oblong, base cuneate, apex with wing extending to form a beak, 6.5–15.5 × 2.3–3.9[–4.3] cm, wing 5–9 mm wide; fruit surface glabrous to sparsely tomentose, sometimes with hairs only at base; venation reticulate, raised and clearly visible on fruit body, anastomosing and somewhat raised and visible on the wing; hypanthium persistent. Seeds 2–5 per fruit; elliptic, visible in outline on fruit exterior when mature, ca. 8–11 × 6–9 mm, brown.

A TAXONOMIC REVISION OF MEZONEURON

Phytotaxa 274 (1) © 2016 Magnolia Press • 7

8 • Phytotaxa 274 (1) © 2016 Magnolia Press

CLARK

Distribution: — Liberia, Ghana, Guinea-Conakry, Cameroon, Gabon, Congo, Rwanda, Burundi, Uganda,

Kenya, Tanzania, Zanzibar, Mozambique, Zambia, Angola ( Fig. 2 ).

Habitat and Ecology: —Moist evergreen forest; secondary forest; grassland; scrub; roadsides. Elevation 90–1900 m.

Phenology:—Flowering and fruiting throughout the year.

Preliminary Conservation Assessment: —Extent of Occurrence 8,238,225.345 km 2 = LC; Area of Occupancy 216.000 km 2 = EN.

Category assigned:—Least Concern (LC).

Taxonomic notes:—The indumentum of the ovary of M. angolense varies from being completely glabrous, to partially to densely tomentose. The distribution of populations with a hairy ovary corresponds broadly with the Guineo-Congolian phytogeographical region ( White 1979), of which the dominant vegetation types are rainforest on well-drained sites and swamp forest on hydromorphic soils ( White 1983). Those with a glabrous ovary correspond with the Swahelian regional centre of endemism and the Swahelian-Maputaland regional transition zone ( Clarke 1998), of which the dominant natural climax vegetation is wet and dry forest, but has largely been replaced by secondary wooded grassland and cultivation ( White 1983).

Figures

FIGURE 2. Distribution of M. angolense in Africa, showing specimens with hairy (squares), slightly hairy (circles), and glabrous (triangles) ovaries.