Psoralea purpurascens 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

2. Psoralea purpurascens C. H. Stirt. & Muasya nom. nov.

Fig. 3

Psoralea cephalotes Eckl. & Zeyh. ( Ecklon and Zeyher 1836: 230), nom. illeg.; non Psoralea cephalotes C. Presl. ex J. Presl ( Presl 1835: 182); non Psoralea cephalotes E. Mey. ( Meyer 1836: 87), nom. illeg.

Type

SOUTH AFRICA – Eastern Cape Province: 3024 (De Aar) • “ In humidis laterum montis Winterberg prope Phillipstown ” (– AD); Ecklon & Zeyher s. n.; lectotype (designated here): S [ S 14-41723 ] pro parte; isolectotype: S [ S 14-41744 ] .

Diagnosis

Psoralea purpurascens is most closely related to P. stachyera . P. purpurascens is a straggling shrub up to 2 m tall ( P. stachyera a larger, virgate, and laxly branched up to 3 m tall, sometimes tree-like); hairs on young leaflets restricted to the margins and adaxial vein, and glands are larger and more raised ( P. stachyera hairier all over becoming glabrescent, glands smaller); standard petals with scarcely reflexed sides and mostly purple with a large white nectar patch fringed with a broad deep purple halo with purple streaks ( P. stachyera with standard petals pink with deep violet-pink nectar patches, sides reflexed).

Description

Straggling shrub up to 2 m tall, regenerating from seed after fire episodes. Stems tan with storied lenticels. Branches appressed white pubescent in young shoots, hairs pointing towards apex. Leaves digitately trifoliolate, partly conduplicate, stipulate, shortly petiolate. Leaflets subequal, terminal 19–25 × 9–10 mm, sometimes much reduced and smaller on seasonal shoots, especially towards the terminal inflorescence, laterals somewhat smaller; symmetrical, apex emarginate, mucro sharp, arching to recurved, 1 mm long, base cuneate, obovate; glands black and crateriform when dry appearing pitted on lower surface, more or less equal, numerous, about the same number on each surface; young leaflets hairy on midrib and margins, persisting in mature leaflets only on the midrib; petiole 2–3 mm long, petiolules 1–2 mm long. Stipules 3–5 × 2 mm, clasping, subulate, sparsely hairy, persistent, very glandular. Inflorescences terminal on 4–5 cm long, densely leafy, seasonal shoots; 20–30 mm long, elongating during anthesis, each comprised of 15–20 triplets of 3–5 mm pedicellate flowers; triplet bracts 4 × 2 mm, broadly lanceolate, 7–8 - veined, becoming narrower and longer up the inflorescence, apex apiculate. Flowers 6–7 mm long, purple, pedicel 1–2 mm long. Calyx 4–6 mm long, glandular, tube 3 mm long, white-haired, lobes unequal, teeth lanceolate, acute, ciliate, glabrous on inner surface, carinal lobe longest 5–6 × 1.5 mm, other teeth equal, shorter and narrower. Standard petals 6 × 4–6 mm, purple, with a broad white nectar guide surrounded by an arc of purple, and suffused with purple streaks, narrowly obovate, appendages and auricles hardly developed, blade narrowed into a short-channelled claw. Wing petals 6–7 × 2 mm, longer than keel, cultrate with terminal end of blade expanded; claw straight, 3 mm long; sculpturing upper mid comprised of 10–12 transcostal lamellae. Keel petals 4 × 1.5 mm wide, obtuse, convex; claw 4 mm long. Androecium 7 mm long, 10 th stamen free, fenestrate. Pistil 4 mm long; ovary 1.5 mm long, ellipsoid, glabrous, 1 - ovulate; style 4 mm long, filiform, thickened before flexure, glabrous; height of curvature 1 mm, stigma small, capitate. Fruits and seeds unknown.

Distribution and habitat

Psoralea purpurascens is distributed mainly in the Eastern Cape Province from Makhanda (Grahamstown) eastwards along the Great Escarpment (Fig. 2 ) with an outlier in KwaZulu-Natal Province. It favours grassland on rocky slopes overlying Gabbro Formation sandstone and Witteberg quartzite, and occurs across a broad range of grassveld, thornveld, and thicket vegetation types: Ngongoni Veld (SVs 4), Amathole Montane Grassland (GD 1), Drakensberg Foothills Moist Grassland (Gs 10), Midlands Mistbelt Grassland (GS 9), Umtatha Moist Grassland (Gs 14), Bisho Thornveld (SVf 7), Eastern Cape Escarpment Thicket (AT 13), Great Fish Thicket (AT 11), Buffels Thicket (AT 12), Northern Coastal Forest margins (( FOz 7), and one fynbos outlier on Suurberg Quartzite Fynbos (FFq 7) (Mucina and Rutherforld 2006). The species favours southern and western aspects at 875–1500 m a. s. l. It is likely that this species will be found to be more common and widespread than is currently known as the central section of its range is a poorly explored mountain escarpment system. It is geographically separated from P. stachyera which is primarily coastal extending to the southern slopes of the first range of mountains stretching from Mossel Bay eastwards to the Mbashe River mouth.

Phenology and ecology

Flowering mainly between December and April but also sporadically at other times of the year. The species especially favours misty grassland, forest margins, and thickets. It has been reported to die off in the winter at higher elevations.

Etymology

The specific epithet purpurascens is a Latin word meaning purple and refers to the dominant colour of the standard petal of the flowers.

Preliminary IUCN conservation assessment

This species has an EOO of 89,250 km 2 classifying it as Least Concern and an AOO of 96 km 2 classifying it as Endangered. Given its wide distribution in the Eastern Cape Province and less so in KwaZulu-Natal Province, Psoralea purpurascens may be threatened by too frequent fires, village expansion, overgrazing, and alien vegetation. However, as most of the known collections have been made along roadsides such populations are very threatened by roadside construction. Few collections have been made beyond roadsides so it should be looked for in remaining vegetation away from roads. Given the large EOO, P. purpurascens does not meet the criteria for Endangered or Vulnerable under B 1 (EOO - based thresholds). However, the small AOO, habitat fragmentation, and multiple threats suggest a Vulnerable (VU) listing, as its habitat is declining in quality and extent. The species is therefore classified as Vulnerable: VU B 2 ab (iii, iv) ( IUCN 2012).

Additional specimens examined

SOUTH AFRICA – KwaZulu-Natal Province: 2829 (Harrismith) • Ukuhlamba (– CC); 15 Jan. 2008; Muasya & Stirton 3711; BOL . – KwaZulu-Natal Province: 3029 (Kokstad) • Tabankulu, Transkei (– CD); 17 Apr. 1996; Cloete 3423; KEI • Weza (– DA); 16 Dec. 1981; Stirton 10415; NH . – KwaZulu-Natal Province: 3030 (Port Shepstone) • Mpenjati Nature Reserve (– AA); 4 Jul. 1997; Von Fintel 555; NH • Mpenjati Nature Reserve (– CD); 13 Dec. 2001; Peter 437; NU . – KwaZulu-Natal Province: 3130 (Port Edward) • Mpenjati Reserve, Port Edward (– AA); 4 Apr. 1995; Abbott 6742; NH • ibid.; 23 Jun. 1991; Nicholson 2786; NH • ibid.; Aug. 1992; Nicholson 2804; NH . – Eastern Cape Province: 3225 (Somerset East) • Farm Glen Avon 74, Summit plateau of Boschberg (– DA); 13 Nov. 2008; Clark & Coombs 1064; BOL, GRA . – Eastern Cape Province: 3226 (Fort Beaufort) • near Grahamstown (– AD); Bolton s. n.; TCD • Howieson’s Poort (– AD); 1869; MacOwan 131; NH • Mountain Summit, Grahamstown (– AD); 10 Aug. 1999; Davies & Rothman 27; GRA • ibid.; 19 Aug. 1999; Davies & Rothman 28; GRA • ibid.; 1869; MacOwan 314; BOL, NH • ibid.; 17 Aug. 1990; Rapson & Turner 18; GRA • ibid.; 17 Aug. 1990; Cummings & Waldrick 28; GRA • Mountain Drive, Grahamstown ; 10 Aug. 1990; Davis & Rothman 27; GRA • Mid-reaches of Katberg Pass, Fort Beaufort District (– BC); 30 Jan. 2009; Clark, Pienaar & Daniels 725; BOL, GRA • Path to Featherstone Kloof ; 18 Jun. 1961; Heeg 113; GRA • Fort Fordyce (– CB); 12 Mar. 1947; Storey 2106; GRA, PRE • Sandile’s Kop, Transkei (– DD); Jan. 1989; Edwards 498; NU . – Eastern Cape Province: 3227 (Stutterheim) • Fort Cunynghame (– AD); 12 Jun. 1972; Van Gadow 149; GRA • ibid.; 1897; Sim s. n.; PRE [20288] • Cata Valley ; 22 Mar. 1950; Acocks 15746; PRE • Mountains W of Keiskamma River Valley (– CA); 25 Jan. 1957; Gibbs Russell 3498 a; GRA, NU • Kubusie State Forest north of Stutterheim (– CB); 7 Dec. 2001; Meyer 1025; PRE • Dohne Peak (– CB); 5 Jul. 1942; Acocks 8956; PRE • Mt. Kemp ; 13 Jan. 1947; Leighton 2750; BOL • Old Cwence Sawmill site, Amatola Range (– CB); 3 Aug. 1984; Duckworth 74; NH • Kingwilliamstown (– CA); 1881; Tyson 1020; SAM • Komgha (– DB); 1890; Flanagan 403; BOL, GRA, NH, PRE . – Eastern Cape Province: 3228 (Butterworth) • Dwesa Forest, Willowvale (– BA); Jul. 1937; J. D. W. Van der Merwe s. n.; BM, NH . – Without precise locality • Robinson’s Drift ; 22 Dec. 1892; Grant 2739; BOL .

Notes

This species has been overlooked since it was first described illegitimately. It is most closely related to Psoralea stachyera Eckl. & Zeyh. , within which it was included by Harvey (1862) and Forbes (1936). Stirton (1989) noted that the two species were quite distinct at the extremes of their range but that there was an overall gradation from the southwest to the northeast in inflorescence and flower size, flower colour, degree of pubescence, and robustness of the plants. Recent field work and new collections have enabled a clearer distinction. We have only come across two specimens of P. cephalotes that may be considered as type material. The first candidate is a mixed sheet at S. The righthand specimen on the S 14-41723 sheet is selected here as the lectotype. The other two twigs belong to P. bracteolata Eckl. & Zeyh. The other S specimen (S 14-41744) is more depauperate and is unlikely to have been used as the basis to describe the species. The Ernst Meyer name refers to P. uncinata Eckl. & Zeyh. and is an illegitimate name.

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 3. Psoralea purpurascens. A. Habit. B. Section of shoot showing upper surface of mature leaves. C. Branches with terminal inflorescences. D. Inflorescences. E. Inflorescence. Photographs from iNaturalist: A: https://www.inaturalist.org/observations/103088515, Emma Ferreira; B, C: https://www.inaturalist.org/observations/181416887, Felix Riegel; D: https://www.inaturalist.org/observations/69730347, Craig Peter; E: https://www.inaturalist.org/observations/22843644, Craig Peter.