Polhillia involucrata (Thunb.) B.-E.van Wyk & A.L. Schutte

du Preez, B., Dreyer, L. L., Stirton, C. H. & Muasya, A. M., 2021, A monograph of the genus Polhillia (Genisteae: Fabaceae), South African Journal of Botany 138, pp. 156-183 : 179-181

11. Polhillia involucrata (Thunb.) B.-E.van Wyk & A.L. Schutte ( Fig. 20 ), Kew Bulletin 44(3): 420 (1989).

Argyrolobium involucratum (Thunb.) Harv. Fl. Cap. 2: 75 (1862). Genista involucrata (Thunb.) Briq. Etude Cytises Alpes Mar. 119 (1894). Melolobium involucratum (Thunb.) C.H.Stirt. S. Afr. J. Bot. 52: 4 (1986). Psoralea involucrata Thunb. Prodr. 136 (1800); Fl. Cap. 607 (1823).

Type: South Africa, Cape, without precise location, Thunberg s.n. ( UPS-THUNB 17575 , lecto.!, chosen by Stirton , 1986b) .

Erect, rounded shrubs to 0.4 — 1.0(— 1.5) m tall, sprouting from woody rootstock. Branches greyish-brown, smooth, densely villous on young stems, sparsely villous on old stems, lenticels absent. Stipules 4.0 — 10.0 mm long, green, glabrous abaxially, villous adaxially, 3 veins prominent. Lea fl ets obovate, glabrous, sparsely hairy on abaxial surface and margin of young leaves only partially reflexed, midrib sunken, conduplicate, partially flattened during wet season, apex apiculate-acute, base broadly attenuate, terminal leaflet 3.0 — 9.0 X (1.0 —)2.0 — 4.0(— 6.0) mm, lateral leaflets 2.5 — 8.0 X 1.0 — 4.0(— 5.5) mm; petiole 1.0 — 3.0 mm long. In fl orescence 2 — 5(— 6) flowered terminal cluster, subsessile, subtended by enlarged stipules that look like involucral bracts; pedicel up to 6.0 mm long, villous; bracts unknown. Flowers dark pink or rarely white, 10.0 — 12.0 mm long. Calyx ± 7.0 mm long, flushed red, darker on teeth, sparsely pilose, but denser on and inside teeth; tube 4.0 — 5.0 mm long; dorsal teeth triangular, 2.0 — 3.0 mm long, fused for less than one third their length, tips acute; ventral teeth narrowly triangular, 2.0 — 3.0 mm long, fused for ± half their length, spreading, apex acute. Standard 11.0 — 12.0 mm long, claw lanceolate, about 4.5 mm long; lamina broadly elliptic, dark pink, apex emarginate, base broadly attenuate, 6.5 — 7.5 X 6.0 — 7.0 mm, back pilose along midrib. Wing petals 10.0 — 11.0 mm long, paler than standard, equal to or slightly longer than keel; claw (3.0 —)4.0 — 4.5 mm long; lamina broadly oblong, glabrous, apex rounded-obtuse, base truncate, 7.0 — 7.5 X 3.5 — 4.0 mm, oval depression above with lamellate sculpturing prominent to apex. Keel petals 9.0 — 11.0 mm long, hyaline along upper half, flushed pink on lower half; claw 4.0 — 4.5 mm long; lamina navicular, 6.2 — 7.0 X 3.0 — 3.5 mm, pilose on fore half, apex obtuse, base truncate to slightly auriculate. Stamens basifixed anthers 1.1 — 1.2 mm long, carinal anther 0.9 — 1.0 mm long, dorsifixed anthers 0.6 — 0.7 mm long; staminal tube 8.9 — 9.1 mm long, unfused portion of filaments remaining equidistant, loosely arranged around the style. Pistil 10.1 — 11.5 mm long; ovary 5.7 — 6.3 X 0.9 — 1.1 mm, ovules 7; style usually at about 60 — 70̊ angle, height of curvature 1.8 — 2.2 mm, glabrous except basally. Fruit dehiscent, opening along two sutures, non-plicate, woody, sericeous and somewhat glabrescent, pale brown to beige, 23.0 — 29.0 X 3.0 — 4.5 mm. Seed ovate-squared; testa olive-green to dark-brown, marbled pale orange, smooth, 2.4 — 2.7 mm long, 2.1 — 2.4 mm wide, 1.5 — 1.9 mm thick.

Etymology

The specific epithet “involucrata ” refers to the enlarged terminal stipules that surround flowers in the bud stage similar to an involucral bract.

Diagnostic characters

Polhillia involucrata is characterized by having dark pink flowers, which is unique among SA Genisteae , of which flowers are primarily yellow, rarely white. The glabrous or rarely sparsely pilose leaves and stipules (versus pubescent leaves and stipules in other Polhillia species); enlarged terminal stipules (versus small terminal stipules); and dehiscent fruit (versus indehiscent fruit) are also diagnostic of this species, and distinguishes it from all other Polhillia species.

Distribution, ecology and conservation status

Polhillia involucrata flowers from October to December. This species was previously only thought to occur in two regions of the Roggeveld escarpment ( Fig. 21 ) where it grows in Roggeveld Shale Renosterveld (FRs 3) ( Mucina and Rutherford, 2006). An isolated collection was, however, made in 2003 (Gwynne-Evans 818) along the R318 between Touwsriver and Montagu. The more widespread occurrence in this area was confirmed when flowering specimens were discovered and collected in October 2017 ( B. du Preez & Stirton 397) several kilometres north of the 2003 collection in Matjiesfontein Shale Renosterveld (FRs 6) ( Mucina and Rutherford, 2006). This represents only the third known location of P. involucrata . It may be more widespread and further exploration, especially after fire, may reveal more populations. It appears to favour relatively flat sandy areas at high altitudes (1000 m.a.s.l. and higher) in shale Renosterveld where it is relatively cool and moist. The generation length is unknown, but is expected to be less than 50 years ( Raimondo et al., 2009). It is threatened largely by overgrazing, habitat loss due to ploughing, and a lack of fire in most areas. Climate change is also likely to threaten the long-term survival of this species due to the lack of suitable habitat remaining around existing populations. The population at Kanariesfontein is on the brink of extinction, as there are only about 10 individuals left in an area which is annually grazed in vegetation that is> 60 years old and drier than the other two areas. The population on the wide road verge around Blomfontein is large with several hundred plants that look healthy. It has burnt recently and has a low browsing pressure. The population found along the R318 growing in a road cutting only includes 6 plants. The Red Data List status of this species is proposed as EN B 1ab(i,ii,iii,iv,v) + B 2ab(i,ii,iii,iv,v) following the latest IUCN categories and criteria ( IUCN, 2012). Flowers are visited by small bees and bee flies.

Additional specimens examined

South Africa. NORTHERN CAPE: 3119 (Calvinia): Roggeveld, turnoff to Blomfontein, in road reserve (— DD), 26 Sept 2009, Helme 6189 (NBG); Roggeveld, along Rooiwal road to Middelpos, Blomfontein (— DD), 27 Sept 2000, H. Rosch 793 (NBG); Farm Blomfontein, Roggeveld escarpment (— DD), 7 Jan 1986, C.H. Stirton 10999 (NBG); Entrance to Blomfontein farm (— DD), 27 Oct 1983, Snijman 778 (NBG); 23 Apr 2017, B. du Preez 279 (BOL); 23 Oct 2017, B. du Preez & Stirton 405 (BOL), 406 (BOL); 17 Dec 1985, A.L. Schutte 397 (JRAU), 398 (JRAU); Nov 1986, M. Steenkamp s.n. sub A.L. Schutte 377 (JRAU), 379 (JRAU); 3120 (Williston): 68 km from Calvinia on Blomfontein road to Middelpos (— CC), 15 Dec 1976, Goldblatt 4614 (NBG); Between Calvinia and Middelpos on Blomfontein road, about 70 km SE Calvinia (— CC), 26 Oct 1976, Goldblatt 4389 (BOL, NBG); Dro ekloof € farm along Blomfontein road (— CC), 23 Oct 2017, B. du Preez & Stirton 402 (BOL, NBG, PRE), 403 (BOL, NBG); 25 km west of Middelpos, near Bo Tuin farm, Roggeveld Escarpment (— CC), 14 Nov 1987, Goldblatt & Manning 8652 (PRE); Kareebank farm south of Blomfontein on Roggeveld escarpment (— CC), 23 Oct 2017, B. du Preez & Stirton 407 (BOL, PRU); 3220 (Sutherland): Sutherland — Kanariesfontein (— AD), Oct 1990, Bayer 6142 (PRE); Kanariesfontein farm behind Populus plantation, Sutherland (— AD), 16 Sept 2011, Boatwright 602 (NGB); 24 Oct 2017, B. du Preez & Stirton 409 (BOL); 3319 (Touwsriver): Road cutting along R318 before tower (— BD), 21 Oct 2017, B. du Preez & Stirton 397 (BOL); Next to R318 (— BD), 25 Mar 2003, Gwynne-Evans 818 (BOL).

Figures

Fig. 20. Composite plate of Polhillia involucrata. 1 — Inflorescence with pink flowers; 2 — Inflorescence with white flowers; 3 — Side view of inflorescence showing pink-flushed sepals; 4 — Calyx; 5 — Flower side view; 6 — Flower bottom view; 7 — Wing petals; 8 — Keel petal; 9 — Androecium; 10 — Gynoecium; 11 — Fruit; 12 — Dehiscent frfrfruit on bush; 13 — Close-up of leaves and stipules; 14 — Habit.Scale bars:4 mm.Photographs by B.du Preez

Fig. 21. Distribution of Polhillia involucrata