Psoralea acocksii 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

1. Psoralea acocksii C. H. Stirt. & Muasya nom. nov.

Fig. 1

Otholobium pustulatum C. H. Stirt., South African Journal of Botany 57 (2): 125. 1991. ( Stirton 1991).

Psoralea pustulata (C. H. Stirt.) C. H. Stirt. ( Bello et al. 2022: 69), nom. illeg.; non Psoralea pustulata F. Muell. ( Mueller 1859: 54).

Type

SOUTH AFRICA – Northern Cape Province: 2917 (Springbok) • 27 km SWW of Springbok ; 24 Sep. 1957; Acocks 19581; holotype: PRE; isotype: K [ K 003992565 ] .

Diagnosis

Psoralea acocksii is most similar to P. flexuosa (C. H. Stirt.) C. H. Stirt. but differs in its low tangled habit with smooth stems ( P. flexuosa a more robust erect laxly branched shrub with densely lenticelled stems); with dull greyish green, elliptic to obovate, flattish leaflets, sparsely sericeous on both surfaces ( P. flexuosa with conduplicate broadly obovate leaflets, sparsely sericeous on lower surface only, and shiny bright green above); with more compact inflorescences at ends of long seasonal shoots bearing white flowers ( P. flexuosa with lax zig-zag like inflorescences bearing greenish-white flowers); and calyx teeth much longer than the long tube ( P. flexuosa with calyx teeth shorter than tube).

Description

Tangled densely branched shrub 0.3–1.0 m tall. Stem branches brownish, pustulate, sparsely lenticelled, appressedly puberulous, striped and grey when younger. Leaves digitately trifoliolate, petiolate. Leaflets unequal; terminal (12 –) 15–16 × 5.0– 6.5 mm, elliptic to obovate, larger than the laterals, all symmetrical; recurved, mucronate, mucro 0.5 mm long; apex emarginate, base cuneate, flat to partly complicate, sparsely sericeous on both surfaces; dull greyish green; petiole 2–4 mm long, persistent once leaflets have dropped; petiolules <1 mm long, sericeous. Stipules 2–3.5 mm long, glabrous, setaceous, straight, caducous. Inflorescences laxly spicate, borne terminally, straight or arching, sparsely leafy; 30–45 mm long, flowers ascending; comprised of 5–8 triplets of shortly pedicellate flowers, each triplet subtended by a rapidly caducous, broadly oblanceolate, pubescent bract. Flowers 8–9 mm long, ebracteate, white; pedicel <2 mm long. Calyx teeth much longer than the 3 mm long tube; equal to subequal (carinal tooth sometimes longer); lanceolate, attenuate, carinal tooth slightly broader, 2 mm wide; vexillary teeth fused for more than half their length, appressedly puberulous, with white and blackish hairs, profusely and evenly glandular over the entire surface but glands larger on the tube. Standard petals 9–10 × 6–7 mm, broadly ovate; apex emarginate, claw 2 mm long, scarcely auriculate. Wing petals 9–10 × 2.5–3.0 mm, claw 4 mm long, auricle prominent, longer than keel petals; sculpturing upper central comprising up to 15 rows of transcostal lamellae. Keel petals 7 × 2.0– 2.3 mm, claw 3–4 mm long, apex obtuse. Androecium 8 mm long, sheath split adaxially, vexillary stamen lightly fused in lower third. Pistil 7 mm long; ovary 2 mm long; sericeous on upper half, stipitate; height of curvature 2 mm, entasis broadest at point of curvature; stigma penicillate. Fruits known from photographs, hairy, glandular, elliptic, flattish, as long as calyx but not emerging. Seeds unknown.

Distribution and habitat

Psoralea acocksii is one of the most north-westerly species of Psoralea in southern Africa and occurs in mountain Renosterveld (Veld Type No. 43; Acocks 1975) at an elevation of 700–800 m a. s. l. (Fig. 2 ). It occupies the Namaqualand Klipkoppe Shrubland (SKn 1) and Namaqualand Shale Shrubland (SKn 2) vegetation types ( Mucina and Rutherford 2006).

Phenology and ecology

Flowering in September and October, fruiting in November. Found occasionally in small populations on yellow brown sandy loam soil on moderate slopes (Nama geological series) with a southerly aspect.

Etymology

The specific epithet acocksii is named after the South Africa plant ecologist John Phillip Harison Acocks (1911–1979). Acocks made a monumental contribution to the knowledge of plant ecology in southern Africa, and collected numerous herbarium specimens, over a career spanning nearly 50 years ( Hoffman and Cowling 2003).

Preliminary IUCN conservation assessment

Psoralea acocksii is a rare range-restricted species with an EOO of 973 km 2 and an AOO of 20 km 2, both classifying it as Endangered. It has a limited seed output and is susceptible to fire. Very little information is available about its status or population density although a few new populations have been discovered since it was described. The species is therefore provisionally classified as Endangered: EN B 1 ab (iii) + 2 ab (iii) due to its restricted range and potential habitat threats ( IUCN 2012).

Additional specimens examined

SOUTH AFRICA – Northern Cape Province: 2917 (Springbok) • North of Nigramoep Kammagas (– BC); Helme s. n.; BOL • Kammagas (– CB); 1 Oct. 1929; Herre s. n.; NBG [ NBG 201680 -0] • Spektakel Pass (– DA); 4 Sep. 1951; Maguire 1009; NBG • 23 km W of Springbok on road to Kleinsee (– DA); Le Roux 2953; NBG . – Northern Cape Province: 3017 (Hondeklipbaai) • Grootberg (– BC); 26 Nov. 2007; Muasya & Stirton 3286; BOL • Without precise locality, Namaqualand; Whitehead 26; MEL [ MEL 1541978 ] .

Figures

Figure 1. Psoralea acocksii. A. Habit and habitat. B. Upper surface of leaflet. C. Lower surface of leaflet. D. Infructescence. E. Side view of fruit. Photographs from iNaturalist: https://www.inaturalist.org/observations/27961328, Brian du Preez.

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