South Africa: Western Cape, Ladismith (3320), Witteberg Private Nature Reserve, Driedamhoek (–AD), at end of jeep track, 33°20'11.7"S, 20°31'57.7"E, 20 February 2011, Muasya, Chimphango, & Stirton 5927 (holotype: BOL!; isotypes: BM!, GRA!, K!, MO!, NBG!, NH!, P!, PRE!).

Habiterect, willowy, flexuose branched shrub to 3 m tall, reseeder but coppices regularly once established. Stems 1(2), brownish-grey with scattered white lenticels, weakly fissured, bare of leaves except on the seasonal shoots which arise in a characteristic burst-branching; shoots coppice seasonally on old stems, leafy along their entire length, glaucous green with a whitish bloom, glabrous, with small raised crateriform glands. Leaves 1-foliolate, petiolate, stipulate, glandular, glabrous. Leaf size variable, being larger on water shoots from the rootstock (20–23 mm long, 2–3 mm wide), becoming smaller up the flowering shoots, dull glaucous green; apex rounded to acute; base cuneate; tip arching; petiole 1–2 mm long. Stipules 1–2 mm long, fused at base, rigid, triangular, semi-patent, 1-veined, rapidly senescent on flowering shoots. Flowers 10.0–12.5 mm long, greenish cream, borne in most axils of the upper half of the seasonal shoots, 1–3 per axil; pedicels 2 mm long. Peduncles 10–12 mm long, purple-tinged, terminated by a small tri-toothed cupulum; cupulum teeth equal, broadly triangular, acute, green, <1.0mm long. Calyx 5 mm long, pale green, sometimes flushed with purple, glabrous; teeth triangular, all 2 mm long, carinal tooth broadest, blunt, weakly ribbed, glandular; tube longer than the teeth, accrescent in fruit, persisting after fruits and seeds are shed. Standard broadly elliptic, 10 mm long, 10–12 mm wide; claw 2 mm long, almost tubular; cream, nectar flash purple rising from above the strongly developed auricles to the apex; inner face of the standard greenish, veins purple; apex emarginate but standard not fully reflexed. Wing petals 10–11 mm long, 4 mm wide; claw 2.5 mm long; locked into keel fold but not fused, slightly longer than the keel, petal sculpturing present, upper basal, comprised of 4–5 transcostal parallel lamellae. Keel petals 10 mm long, 3 mm wide; claw 5 mm long; apex deep purple. Androecium 9 mm long; tenth stamen free; sheath split adaxially, fenestrate. Pistil 9 mm long; ovary 1.5 mm long, sessile, glabrous, thickened before point of flexure, height of curvature 3 mm, erect, penicillate. Fruits ovate, indehiscent, wall scarious, 3.8–4.1 mm long and 2.2–2.5 mm wide at mid length. Seed 3.5–4.0 mm long and 2.1–2.2 mm wide at mid length, dark olive green, smooth, aril present and light olive green.

Psoralea karooensis grows in the Klein Karoo mountains, between 1000–1200 m. It is restricted to the Witteberg quartzite fynbos vegetation, between the Witteberg and Anysberg Mountains, and occurs mainly in gulleys and along the banks of dry river beds (Plate 2).

The specific epithet alludes to its known restriction to the Klein Karoo.

Psoralea karooensis is locally common within its range and much of its distribution occurs in protected nature reserves. However, the species is a habitat specialist (fresh water stream beds with intermittent flow) at above 1000 m and is only known from an area less than 500 km². We therefore assess this species to be Rare under the South African Red list categories and criteria (EOO, AOO; Von Staden et al. 2009).

South Africa: Western Cape: Laingsburg district (3320 AD), Elandsfontein Farm, on dirt road off N1 - Laingsburg via Witteberg [33°18'38.41"S, 20°26'46.13"E], 20 Feb 2011, Stirton, Muasya & Chimphango 13245 (BOL); Witteberg Kloof, 16 Jul 1923, Compton 2592 (BOL). Witteberg, S. base of the range, 31 Jan 1961, Esterhuysen 28844 (BOL, PRE).

Western Cape: Ladismith district (3320 AD), 9 Aug 1939, Levyns 6106 (BOL).

Western Cape: Laingsburg district, at entrance to Perdekloof Gorge, S. of Matjiesfontein at northern base of Witteberg (3320 BC), Helme 2938 (NBG).

Psoralea karooensis is characterised by its small (< 13 mm long) greenish cream flowers with a small (< 1.0 mm long) trifid cupulum at the apex of a 10–12 mm long peduncle, standard with single purple flash nectar patch and purplish veins, 1-foliolate leaves, erect multi-branching short seasonal flowering shoots, and flexuose habit of many stiff bare stems with the seasonal shoots arising apically in clusters. It is most similar to Psoralea glaucescens Eckl. & Zeyh., a widespread but rare species found in the northwestern Cape. The resprouter Psoralea glaucescens differs in its densely branched mounded habit, grey puckered stems, 3–5-foliolate irregularly sized leaves, greenish yellow flowers, with violet veining and nectar flash, borne 1–5 per axil, and purplish calyces.