Xerocladia Harv. in W.H. Harvey & Sonder, Fl. Cap. 2: 278. 1862.

Figs 138, 139, 140

Type.

Xerocladia zeyheri Harv. [= Xerocladia viridiramis (Burch.) Taub.]

Description.

Small, rigid, densely and intricately much-branched shrub to 1 m (Fig. 138A), the branches often somewhat zig-zag, shoots mid- to olive-green, sub-striate; brachyblasts absent. Stipules spinescent, in pairs, recurved (Fig. 138G). Leaves small, bipinnate; petiole with a stipitate reddish-brown gland immediately below insertion of pinnae, unijugate (Fig. 138G); leaflets 6-12 pairs per pina, sub-opposite, usually with a small reddish-brown gland at the base of each leaflet. Inflorescences solitary capitula, in axils of leaves (Fig. 139A). Flowers sessile, dark maroon, young filaments reddish-maroon (Fig. 139A); sepals 5, valvate, free almost to the base; petals 5, valvate, free except at base; stamens 10, free, anthers with a minute, caducous, apical claviform gland arising from the connective; pollen in tricolporate monads, pores with costae, exine smooth, perforated, columellae present; ovary shortly stipitate, stigma truncate. Fruits sessile, indehiscent, broadly falcate-ovate to semi-orbicular, compressed, the lower suture arched and winged, 1 (2)-seeded, valves coriaceous, chestnut- to reddish- or purplish-brown when ripe (Fig. 139H). Seeds sub-circular to elliptical, smooth, pleurogram present, U-shaped, testa hard.

Chromosome number.

Unknown.

Included species and geographic distribution.

Monospecific ( X. viridiramis), endemic to arid parts of Namibia and Namaqualand in southern Africa (Fig. 140).

Ecology.

Arid scrubland in sandy river soils, on riverbanks, alluvium and saline flats.

Etymology.

From Greek, xero - (= dry) and - cladion (= branch), in reference to the dense branching habit typical of small shrubs in arid climates.

Human uses.

Unknown.

Notes.

Xerocladia has long been thought to be closely related to the former Prosopis s.l. (Catalano et al. 2008) with which it shares arid ecology and characteristic green photosynthetic shoots. It is robustly supported as sister to Strombocarpa with which it shares similar armature in the form of spinescent stipules, and unijugate leaves. However, despite these obvious similarities, Xerocladia is a highly distinctive and easily recognised genus, and its small reniform, flattened, indehiscent, 1 (2)-seeded winged fruits are unique within Mimoseae (Fig. 139H).

Material referred to under the name Xerocladia pampeana Speg. from Argentina, shows clear affinities to the genus Prosopidastrum Burkart, as suggested by Palacios and Hoc (2005).

Taxonomic references.

Dyer (1975); Ross (1975a); illustration Fl. Southern Africa 16: 131.