Psoralea vlokii 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

3. Psoralea vlokii C. H. Stirt. & Muasya sp. nov.

Figs 2 , 4 , 5

“ Psoralea vlokii C. H. Stirt. ms. ”, nom. nud., Stirton and Schutte (2012: 574)

Type.

SOUTH AFRICA – Western Cape Province: 3322 (Oudtshoorn) • Northern slopes of the Outeniqua Mountains, Upper reaches of Grootdoringsbosrivier , 3322 CD; 12 Nov. 1986; Stirton & Žantovská 11582; holotype: PRE; isotypes: K, NBG .

Diagnosis.

Species similar to Psoralea trullata C. H. Stirt. but differs in being a sprawling multi-stemmed reseeding shrublet ( P. trullata a tangled multi-stemmed resprouting suffrutex); leaflets 1 - foliolate, 2.5–4.5 mm wide, linear, apex attenuate ( P. trullata 0.5–2.0 mm wide, linear to linear oblong, apex acuminate); stipules 2.0–3.1 (– 3.5) mm long ( P. trullata 5–7 (– 10) mm long); flowers 8–9 mm long, white, standard petal with pale mauve or hyaline veins ( P. trullata flowers 10–12 mm long, purple or purplish-blue, standard petal with dark veins and a distinct nectar guide comprising a white flabellate base topped with a violet fringe); wing petals 7 × 3 mm, not constricted towards the base, auricle not narrow and not peg-like ( P. trullata 14–15 × 3 mm, strongly restricted towards base, auricle almost peg-like); keel 9 mm long, tip of keel short and abruptly acuminate ( P. trullata keel 20–21 mm long, slender, with a long and attenuated beak).

Description.

Low, spreading, glabrous shrublet up to 50 cm tall, reseeder. Stems numerous, slender, terete, finely ridged, glandular; rootstock slender, caudate. Leaves stipulate, 1 (– 3) - foliolate, linear to linear-narrowly oblong but flattening towards the apex, densely covered in sub-epidermal glands. Leaflets 7–13 × 2.5–4.5 mm, slightly grooved along upper surface, base cuneate. Stipules 2.0–3.1 (– 3.5) × 0.5–1.0 mm, fused for two-thirds their length, collar-like, adnate to petiole, narrowing further up the stem. Inflorescence reduced to a solitary axillary flower. Flowers 8–9 mm long, white; stalked; cupulum composed of two long almost free acute teeth opposite a small hemispherical tooth, tube 1 mm deep, inner face of teeth glabrous. Calyx 6 mm long, lobes unequal, carinal tooth much longer than lateral and vexillar teeth, almost boat-shaped, longer than the flower, lateral teeth longer than the falcate and partially fused vexillar teeth, acute; tube 3.5 mm deep; inner face of teeth glabrous, glandular. Standard petals 9–10 × 8–9 mm, broadly elliptic, appearing broadly ovate when standard petal is erect, weakly auriculate, appendages scarcely developed, white with veins from hyaline to pale mauve, flushed with pale green in upper parts, apex acute, tipped green; claw 1.5 mm long. Wing petals as long as the keel blades, 7 × 3 mm, claw 3.0 mm long; upcurved and with the blade flaring strongly sideways from mid-point of the blade; auricle well-developed; sculpturing upper basal with 4–7 transcostal lamellae shortening towards the middle axis of the blade. Keel petals 9 × 3 mm, claw 3.5 mm long, 3.5 mm high from claw axis; apex almost rostrate. Androecium 9 × 2 mm, vexillary stamen free. Pistil 9 mm long, ovary 1.3–1.5 mm long, glabrous; gynophore present, 0.5 mm long; style glabrous, thickened at point of flexure, height of curvature 3.5 mm, stigma capitate, finely penicillate. Fruits and seeds unknown.

Distribution and habitat.

Psoralea vlokii is a rare endemic montane species and occurs on the Langeberg and Outeniqua mountains in the North Outeniqua Sandstone Fynbos (FFs 18) and North Langeberg Sandstone Fynbos (FFs 15) vegetation types ( Mucina and Rutherford 2006) (Fig. 2 ). It can form large colonies and favours permanent swampy seepage with Cliffortia graminea L. f. and Platycaulos compressus (Rottb.) H. P. Linder on wet sandy soils but also occurs on drier slopes in mountain fynbos occurring between 530 and 590 m a. s. l. It has been recorded from Tschando shales and Hutton Series soils.

Phenology and ecology.

Flowering occurs commonly after fires from December to January and thereafter only sporadically. The multi-stemmed appearance also gives the impression that plants emanate from a rootstock, but they clearly germinate after fire (fide Jan Vlok and personal observation). Psoralea trullata , by contrast, occurs at higher altitudes between 1100 and 1600 m a. s. l. and favours steep rocky slopes and ledges with peaty soils overlying Table Mountain Sandstone and has a broader distribution stretching from the Outeniqua Pass to the Great Wintershoek mountains.

Etymology.

The specific epithet vlokii is named after the Cape plant ecologist, botanist, and phytogeographer Jan Vlok who first showed the first author this species in the field, and for his past and continuing outstanding contribution to the study and discovery of plants of the Karoo and for his ongoing mentorship of professional botanists and amateurs who visit the region.

Preliminary IUCN conservation assessment.

Although this species can be locally common after fires little is known about its population density or perseverance after fire. However, like P. trullata , the unique rare, red-flowered P. implexa C. H. Stirt. (DuToitskloof), and P. cataracta C. H. Stirt. (Northern Tulbagh valley) it is difficult to find in the veld or identify in its restioid-like vegetative state, which probably accounts for their supposed rarity. The known observations and collections of P. vlokii cluster across 320 km of mountain ranges and have been found mostly on either side of the Tradouw, Garcia, and Outeniqua passes with little known of the largely intervening areas so it can be expected to be more common than encountered so far. Vlok and Raimondo (2007) assessed it as Endangered: EN B 1 ab (iii, v). However, since then it has been found in more locations so it needs to be reassessed. They noted that in 2007 it occurred in an EOO of <250 km 2, from five locations which were declining due to dense alien pine and Hakea Schrad. invasion of the habitat, and that it was also likely to be overly sensitive to water extraction. Although these threats are still present, the broadening of its distribution range suggests lowering its conservation status (Jan Vlok pers. comm.).

Additional material examined.

SOUTH AFRICA – Western Cape Province: 3322 (Oudtshoorn) • Next to forestry track along Grootdoringsrivier , Northern slopes of the Outeniqua mountains; 8 Oct. 1985; Vlok 1271; K, NU, PRE • Upper tributary of the Moordkuils , southern foothills of the Outeniqua mountains (– CC); 1985, Vlok 1354; K, PRE • Near Kleindoringsrivier , lower northern slopes of the Outeniqua Mountains (– CD); 14 Nov. 1984, Stirton 8650; K, NU .

Observations.

South Africa, Western Cape Province: Huisrivier tributary, east of Barrydale, Langeberg, 3 Mar. 2019, obs. by Lennartn, https://www.inaturalist.org/observations/21105626; Eden, Camferskloof, 21 Oct. 2019, obs. by Nicky van Berkel, https://www.inaturalist.org/observations/34962095; ibid., 25 Oct. 2019, obs. by Nicky van Berkel, https://www.inaturalist.org/observations/34962095; ibid., 25 Oct. 2019, obs. by Nicky van Berkel, https://www.inaturalist.org/observations/34962102; ibid., 26 Feb. 2019, obs. by Nicky van Berkel, https://www.inaturalist.org/observations/70278510; ibid., 14 Nov. 2021, Nicky van Berkel, https://www.inaturalist.org/observations/101187196.

Figures

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

Figure 4. Psoralea vlokii. A. Jan Vlok holding a plant. B. Whole plant in habitat. C. Side view of flower showing cupulum and subtending leaf. D. Frontal view of flower. E. Flower bud. F. Side view of flower showing cupulum and subtending leaf. G. Fruiting calyx. H. Frontal view of flower showing variation in colour. Photographs: B by Charles Stirton; A, F, H by Brian du Preez; D by Dave U; C, E, G by Nicky van Berkel.

Figure 5. Psoralea vlokii. A. Habit. B. Frontal view of flower. C. Adaxial view of opened calyx. D. Adaxial view of stipules fused to the petiole. E. Cupulum. F. Standard petal. G. Wing petal. H. Keel. I. Pistil. Artist: Elenor Cathrine.