Psoralea albidula C. H. Stirt. & Muasya, 2025

Stirton, Charles H., Bello, Abubakar & Muasya, A. Muthama, 2025, Nomenclatural notes on the genus Psoralea (Psoraleeae, Fabaceae) in South Africa, Plant Ecology and Evolution 158 (2), pp. 168-180 : 168-180

4. Psoralea albidula C. H. Stirt. & Muasya nom. nov.

Fig. 5

Psoralea parviflora E. Mey. , Commentariorum de Plantis Africæ Australioris 1: 86. 1836. ( Meyer 1836: 86), nom. illeg.; non Psoralea parviflora (Pursh) Poir. ( Lamarck and Poiret 1816: 590) = Astragalus gracilis Fraser ex Nutt.

Psoralea tauschiana Steud. ( Steudel 1841: 408), nom. superfl.

Psoralea parviflora Tausch ( Tausch 1836: 420), nom. illeg.

Otholobium parviflorum (E. Mey.) C. H. Stirt. ( Stirton 1986: 3), comb. nov. illeg.

Psoralea parviflora (C. H. Stirt.) C. H. Stirt. ( Bello et al. 2022: 68), nom. illeg.

Type

SOUTH AFRICA – Western Cape Province: 3319 (Worcester) • “ Dutoitskloof , III A e ”; Drège s. n.; lectotype (designated by Stirton 1986): K [ K 000392537 ]; isolectotypes: G [ G 00022520 , G 00022521 ], GBH [ GBH 63919 ], HAL, L, LE, MO, P [ P 03050155 , P 03050158 , P 03050159 ], PRC, PRE .

Diagnosis

Psoralea albidula shares a few features with P. obliqua E. Mey. such as short resprouting shrubs with verrucose shoots, digitately 3 - foliolate flat leaflets, and keel petals shorter than wing petals. It has in the past been incorrectly identified or confused with the sympatric species P. obliqua but is easily separated by green finely pubescent young shoots ( P. obliqua purplish patently hairy young shoots); flat straight leaflets with a shortly recurved-mucronate apex ( P. obliqua apex aristate-mucronate); lateral leaflets almost symmetrical ( P. obliqua strongly asymmetrical); inflorescences densely racemose terminal, on leafy shoots 90–100 m long, comprised of 23–25 triplets of sessile flowers ( P. obliqua borne in the upper 3–4 axils of short 60–80 mm long comprised of 3 - flowered axillary inflorescences borne on short 2 mm long peduncles of seasonal shoots, much overtopped by the leaves); cream or white flowers without a nectar patch on standard petals ( P. obliqua pale mauve to purple flowers with dark purple nectar patch), and non-accrescent fruiting calyx ( P. obliqua accrescent).

Description

Suffrutex up to 1 m tall. Stems up to 50, coppicing after fire; verrucose, prominently papillose and glabrescent when young. Leaves digitately trifoliolate, inserted spirally, spreading; terminal leaflet 30–34 × 10–20 mm, elliptic, laterals slightly smaller, scarcely asymmetric; stem leaflets and water shoots are much larger than those borne on seasonal flowering shoots, all leaves becoming smaller upwards towards the apex; apex recurved-mucronate, base truncate, glabrous, densely glandular; rachis channelled above; petiolule 3 mm long, glandular; petiole 2–3 mm long. Stipules 6 × 1.5 mm, recurved-patent, pubescent, rapidly caducous. Inflorescences terminal, densely racemose on leafy shoots 90–100 m long, comprised of 23–25 triplets of sessile flowers, each triplet subtended by a single, pubescent 3–7 × 3.0– 4.3 mm, broadly ovate bract with an acute apex; bracts become smaller near the apex of the inflorescence. Flowers white to pale cream, drying yellow, nectar patch absent, 8–10 mm long. Calyx scarcely longer than the keel blades; carinal lobe longest, 8–9 × 1.5 mm; other lobes 7 mm long; tube 3–4 mm long; yellowish green with carinal lobe and veins a darker green, pubescent and glandular outside, finely pubescent on the inner face of teeth. Standard petals 8.0–9.5 × 6–7 mm, elliptic; nectar guide if present pale cream; claw 2–3 m long, auriculate; appendages absent; apex emarginate. Wing petals 7.0–10.0 mm, longer than the keel; 9 × 3 mm wide with 3.0– 3.5 mm long claw, billowy at tip; sculpturing present, upper central comprised of 1–2 rows of 13 vertical, irregular, transcostal lamellae. Keel petals 4–7 × 2 mm, with 3.0– 3.5 mm long claw. Androecium sheath 6 mm long, split adaxially; vexillary stamen free. Pistil 4.0– 6.5 mm log; ovary 1.5–2.0 mm long, pubescent; height of curvature of style 1.0– 1.7 mm, thickened at point of flexure; stigma small, penicillate. Fruits and seeds unknown.

Distribution and habitat

Psoralea albidula is restricted to the lower slopes of the mountains stretching from the Kogelberg Biosphere Reserve and Jonkershoek in the south to DuToits Kloof Pass in the north (Fig. 2 ). It has overlapping distributions in parts of its range with P. obliqua which grows on Table Mountain Sandstone outcrops, usually along the crests of ridges, whereas the P. albidula occurs at lower elevations on more gentle slopes and sandier soils. Spontaneous intermediate hybrids may be found occasionally growing at the edge of rocky outcrops. The hybrids are erect multi-stemmed, up to 60 stems, with lax branching near the apex bearing spreading leaves, inflorescences that are either axillary (3–5 flowers) or terminal (up to 25 flowers) or in various combinations. The standard petal is pale mauve with a dark mauve nectar patch (e. g. Stirton 9939).

Psoralea albidula is a species of early successional stages in Mesic Mountain Fynbos and occupies the Hawequas Fynbos Sandstone (FFs 10), and Kogelberg Sandstone Fynbos (FFs 11) vegetation types ( Mucina and Rutherford 2006) on Table Mountain Sandstone (Fig. 2 ). Plants tend to be colony-forming. Flowers are visited by small bees.

Phenology and ecology

Flowering sporadically throughout the year but with a peak between October and December.

Etymology

The specific epithet albidula is a Latin adjective meaning “ whitish ” that refers to the colour of the flowers.

Preliminary IUCN conservation assessment

Potter (2005) classified this species as Least Concern (LC). The species has an EOO of 2,494 km 2 and AOO of 56 km 2, both classifying it as Endangered. However, most populations are in protected areas and no populations are threatened by alien plants. Since no major threats are observed, the Potter (2005) assessment is hereby upheld. The species is classified as Least Concern (LC) ( IUCN 2012).

Additional specimens examined

SOUTH AFRICA – Western Cape Province: 3318 (Cape Town) • mountains near Wellington (– DB); Nov. 1882; Tyson 917; BOL, NH • Jakkalsvlei (– DC); 20 Nov. 1962; Taylor 4377; NBG, PRE • ibid.; 12 Nov. 1965; Taylor 6592; NBG, PRE • Jonkershoek (– DD); 25 Oct. 1950; Parker 4535; BOL, K, NBG • ibid.; 16 Nov. 2007; Muasya & Stirton 3199; BOL • 7 Nov. 1943; Parker 15317; NBG • ibid.; 16 Nov. 2007; Muasya & Stirton 3196; BOL • ibid.; 19 Jan. 1975; Esterhuysen 33749; BOL • ibid.; 3 Jan. 1983; Goldblatt 6812; MO, PRE • ibid.; 10 Nov. 1975; Kruger 49; NBG • ibid.; 13 Dec. 1975; Kruger 33 3; NBG, PRE • ibid.; 9 Nov. 1918; Garside 1163 a; K, STE • ibid.; 14 Dec. 1960; Grobbelaar 249; PRE, PRU • ibid.; 14 Dec. 1966; Grobbelaar 1589; PRE • ibid.; 24 Dec. 1925; Marion s. n.; BOL • Swartboskloof (– DD); 25 Oct. 1960; Van der Merwe 2381; K, NBG, PRE • ibid.; 9 Nov. 1989; Buys 89; NBG, STEU • ibid.; 9 Nov. 1982; McDonald 777; NBG, PRE • ibid.; 28 Oct. 1982; McDonald 855; NBG, PRE • ibid.; 11 Dec. 1975; Kruger 103; STE • ibid.; 9 Jun. 1960; Van Der Merwe 2221; STE • ibid.; 18 Sep. 1960; Van Der Merwe 2358; STE • ibid.; 17 Oct. 1960; Van Rensburg 2120; NBG, PRE • Langrivier Catchment (– DD); 6 Mar. 1975; Haynes 1011; PRE • ibid.; 19 Dec. 1979; Le Maitre 18; NBG • Stellenbosch golf-course (– DD); 17 Oct. 1960; Van Der Merwe 2120; STE . – Western Cape Province: 3319 (Worcester) • Du Toits Kloof Pass (– CA); 10 Nov. 1959; Acocks 20635; K, PRE • ibid.; Jan. 1880; Bolus 5158; BOL, K • ibid.; 25 Oct. 1960; Gentry & Barclay 18729; K, PRE, US • Elandspad, Du Toits kloof (– CA); Walters 13444; NBG • Du Toits Kloof Lodge (– CA); 27 Dec. 2007; Muasya & Stirton 3542; BOL • Bushman’s Castle, Franschhoek Mountains (– CC); Esterhuysen 17670; BOL • ibid.; 14 Dec. 1940; Compton 10131; NBG • ibid.; 7 Jan. 1983; Grobbelaar 2704; PRE • ibid.; Dec. 1951; Stokoe s. n.; SAM [ SAM 69596 ] • Bakkerskloof (– CC); 18 Jan. 1978; Van Wilgen 218; STE • Drakenstein Mountains (– CC); Jan. 1812; Tyson 2436; NH • Bergrivier Hoek (– CC); 1 Jan. 1940; Anonymous s. n.; NBG . – Western Cape Province: 3418 (Simonstown) • Aries Kraal (– BD); 18 Nov. 1944; Leighton 767; BOL • ibid.; 26 Dec. 1941; Bond 1303; NBG • ibid.; 11 Nov. 1944; Compton 16472; NBG • ibid.; Nov. 1944; Lewis 915; SAM • boundary of Kogelberg State Forest and Somersfontein Farm (– BD); 22 Nov. 1974; Boucher 2691; NBG • 2.6 km from Stokoe Bridge, Kogelberg ; 6 Oct. 1993; Kruger 1166; NBG . – Western Cape Province: 3419 (Caledon) • Sutherland farm overlooking Palmiet River of Farm 152, South of Jutland ; 1 Apr. 2011; Anonymous s. n.; NBG • near Elgin, between Grabouw and Paardeberg (– AA); Dec. 1947; Stokoe s. n.; SAM [ SAM 56394 ] • ibid.; 7 Dec. 1984; Jaarsveld & Sardien 7682; NBG • Baileys Peak ; 19 Nov. 1967; Esterhuysen 31806; BOL • Berg Rivier Hoek ; 16 Dec. 1945; Esterhuysen 12408; BOL • Verlorenkloof ; s. d.; Geertse s. n.; PRE • Abdol’s kloof, Jonkershoek ; 28 Oct. 1940; Levyns 7346; BOL • Elgin ; s. d.; Helme 2011; NBG • Bushmans Castle, French Hoek District; 25 Dec. 1936; Salter 6551; BOL . – Without precise locality • Burmann s. n.; G .

Figures

Figure 2. Known distribution of the six described Psoralea species. Map by Abubakar Bello using QGIS v. 3.28 (QGIS Development Team 2020).

Figure 5. Psoralea albidula. A. Habitat. B. Habit. C. Leafy shoots. D. Lower surface of leaflets. E. Inflorescence showing flowers. F. Infructescence showing calyces after fruit shedding. Photographs from iNaturalist: A, B, C, E: https://www.inaturalist.org/observations/37245764, Charles Stirton; D: https://www.inaturalist.org/observations/10815095, Tony Rebelo; F: https://www.inaturalist.org/observations/102157768, Ismail Ebrahim.