Psoralea pallescens C. H. Stirt. & Muasya, 2024

Stirton, Charles H., Bello, Abubakar & Muasya, A. Muthama, 2024, Ten new species and notes on the genus Psoralea L. (Psoraleeae, Fabaceae) from South Africa, Plant Ecology and Evolution 157 (3), pp. 291-312 : 291-312

4. Psoralea pallescens C. H. Stirt. & Muasya sp. nov.

Figs 2 , 6

Type.

SOUTH AFRICA – Western Cape Province: 3419 (Caledon) • Southern slopes of mountains north of Riviersonderend , 3419 (– DC); 34 ° 08 ’ 7.87 ” S, 19 ° 53 ’ 57.07 ” E; 19 Nov. 1980; C. H. Stirton 8219; holotype: NBG; isotype: K .

Diagnosis.

Species similar to Psoralea usitata C. H. Stirt. but differs in its reseeding habit ( P. usitata resprouting); 1 - foliolate leaves ( P. usitata leaves reduced to appressed scales), branches and branchlets stiffly erect ( P. usitata arching to drooping), stipules bifid ( P. usitata stipules 1 - fid); flowers pale mauve, 17–18 mm long, faintly sweetly smelling ( P. usitata purple and white, 9–14 mm long, unscented); pedicels 8–9 mm long; cupulum trilobed, teeth equal ( P. usitata 2–3 mm long, cupulum bilobed with one of the pair bifurcate); calyx teeth about equal to calyx tube, margins not ciliate ( P. usitata calyx teeth shorter than calyx tube, margins ciliate); calyx strongly accrescent, swollen and fleshy, berry-like, teeth tightly closed during seed maturation, shiny and oily, becoming papery and accrescent in fruit ( P. usitata slightly accrescent, never berrylike, with teeth erect).

Description.

Virgate shrub up to 2.2 m tall, colonial reseeder. Stems 1–3, glabrous. Branches erect and stiff even when in flower. Seasonal shoots green, rounded with 10–12 fine grooves in cross-section, glandular, clustered on last season branch tips; previous season’s wood green with brown flaky bark. Leaves 1 - foliolate, spirally arranged, appressed to shoot, up to 18 × ± 1 mm, becoming shorter towards apex of shoots, very narrowly obovate, brownish yellow, glabrous, persistent, laterally compressed and hemispherical in cross-section, with 1 mm long mucro, glandular (translucent against the sun); rachis 1.0– 1.5 mm long, yellowish; petiole <2 mm long. Stipules ascending, bifid, 1 - nerved, green with yellowish tips, glandular, triangular, 2 mm long. Inflorescences borne in most upper axils of seasonal shoots with one flower per axil; buds glabrous; peduncles absent, bracts minute; pedicels 8–9 mm long; cupulum trilobed, teeth equal, 4 mm long, situated on pedicel one third up from the base, glabrous, lobes triangular, acute, gland-dotted. Flowers 17–18 mm long; axillary, one per axil, held at 30 ° from stem, pale mauve, veins not discoloured; maturing sequentially up the shoot; faintly sweet-scented. Calyx glabrous, lobes subequal, with keel tooth 1 mm longer than others; about equal to calyx tube; carinal tooth 8 mm long, acute; vexillar calyx lobes fused 2.5 mm from apex; tube 4 mm long; calyx shorter than corolla; inner face of calyx teeth densely covered in black stubby hairs, margins not ciliate; vexillar tooth purplish, rest green; strongly ribbed; prominently glandular, glands constant in size, same density all over, drying orange; fleshy and berry-like during seed maturation with teeth tightly closed, shiny and oily, becoming papery, orangey brown and accrescent in fruit. Standard petal s 15–17 × 16 mm; broadly ovate, pale mauve but darker towards the apex, nectar patch a dark narrow purple central strip, often absent, veins not coloured; 2 free vertical curved 2 × 3 mm, narrow, white appendages present 2 mm above claw; auricles well-developed, almost tubular when pressed together with anthesis; apex emarginate; claw 5 mm long. Wing petals 16 × 6 mm, longer than keel petals; pale mauve, narrowly cultrate, straight, hooded and touching when viewed from front, furrowed from auricle to tip, sculpturing present, upper basal, with up to ten lamellae transcostal lamellae; fused to keel petals near base; apex rounded; claw 7 mm long. Keel petals 13 × 7 mm, tip discoloured with an oblong-shaped purple discolouration otherwise white, apex acute; claw 6–7 mm long. Androecium 13 × 2 mm when closed, tenth filament mostly free but slightly adherent in lower third. Pistil 12 mm long, ovary 1.5 mm long; style filiform, 9 mm to point of flexure, glabrous but with few stalked club-shaped glands on ovary; pedicellate, gynophore 0.5 mm; height of curvature 4.5 mm, stigma penicillate. Fruits 6 × 4 mm, papery, reticulate, black, oblong. Seeds 4 × 5 mm, brownish black; hilum white, raised 0.5 mm.

Distribution and habitat.

Psoralea pallescens is currently known from the Riviersonderend Mountains from Greyton to Riviersonderend (Fig. 2 ). It is restricted to terraces on rocky southern open slopes on Table Mountain Sandstone in Greyton Shale Fynbos (FFh 7) at 250–300 m a. s. l. and on the NW aspect of seasonally waterlogged sandstone streambanks ( Rebelo et al. 2006).

Phenology and ecology.

Flowering takes place mainly from November to December and sporadically up to June. It is unique in the genus Psoralea in having a strongly accrescent calyx that swells into a shiny, oily, fleshy, berry-like structure during seed maturation by the teeth enclosing tightly into a closed structure. When the seed is mature, and the conditions are right the calyx dries out, the teeth open and the single papery, reticulate, black, oblong fruit becomes exposed. At this point, the calyx is covered in dark orange glands. Dispersal usually happens under windy conditions when the stiff branches are shaken by wind and the papery fruit is expelled. Dispersal is primarily by wind and secondarily by water as the light papery fruits float easily and may wash away from the zone of ejection. It grows at a lower altitude or in valleys, sometimes higher up, than does P. usitata which is a montane species of seepages and stream banks at higher altitudes.

Etymology.

The specific epithet pallescens (Latin ‘ pallescens’ = becoming pale) alludes to the pale mauve flowers.

Preliminary IUCN conservation assessment.

This reseeding species is quite common where it occurs in large colonies. It can be expected to be found elsewhere on the Riviersonderend Mountains, but the area is surprisingly under-collected. It has a narrow distribution range and a small area of occupancy (<2000 km 2), hence based on the IUCN criteria ( IUCN 2012) its present status corresponds to Vulnerable: VU B 2 ab (i, ii, iii).

Additional material examined.

SOUTH AFRICA – Western Cape Province: 3419 (Caledon) • Greyton-McGregor Hike (– BA); 15 Jun. 2017; Brian du Preez 89; BOL • Groot Toren 181, mid slopes of Riviersonderend mountains (– BB); 1 Apr. 2009; Helme 6025; NBG .

Observations.

South Africa, Western Cape Province: Greyton, Genadendal, 8 Mar. 2020, obs. by Klaus Wehrlin, https://www.inaturalist.org/observations/39702444; Greyton Nature Reserve, 4 Apr. 2021, obs. by Klaus Wehrlin, https://www.inaturalist.org/observations/70687565; Greyton, 16 Dec. 2020, obs. by Matthew Fainman, https://www.inaturalist.org/observations/66699599; Greyton, 8 Mar. 2020, obs. by Klaus Werlin, https://www.inaturalist.org/observations/39702444.

Figures

Figure 2. Known distribution of the ten described Psoralea species. Map by Abubakar Bello.

Figure 6. Psoralea pallescens. A. Habitat. B. Habit of young plant. C. Cluster of fruiting calyces. D. Close-up of opened dried calyx teeth of calyces releasing seeds. E. Stages of fruiting calyx maturation. Calyx strongly accrescent, oily, fleshy, and swollen with the teeth tightly closed during seed maturation. F. Terminal cluster of solitary axillary flowers. G. Habit of mature plant. H. Flowering in upper axils of terminal seasonal shoot. Photographs: A, C – E by Charles Stirton; B, F – H by Klaus Wehrlin.