Polhillia stirtoniana B.du Preez

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 : 178-179

10. Polhillia stirtoniana B.du Preez , sp. nov. ( Fig. 19 )

Type: South Africa, Western Cape, 3420 (Bredasdorp): Bredasdorp Region , Plaatjieskraal farm, farm road leading west (— AD), 7 Aug 2017, B. du Preez 309 ( BOL, holo.!; K, MO, PRU, iso.!)

Erect, rounded shrubs up to 0.8 — 1.2 m tall, often wider than tall, sprouting from a woody rootstock. Branches greyish-brown, glabrescent, terminal burst branching present, forming a closed, dense, umbrella-like canopy when mature; lenticels prominent. Stipules 1.5 — 2.5 mm long, silvery. Lea fl ets linear-narrowly lanceolate, arcuate, silvery, adpressed sericeous, conduplicate, tightly closed during dry season, opening slightly in wet season, apex acute, base cuneate, terminal leaflet 3.0 — 5.5 X 0.5 — 0.7(— 1.0) mm, lateral leaflets 2.5 — 5.5 X 0.5 — 0.7(— 1.0) mm; leaves subsessile. In fl orescence 1(— 2) flowered terminal cluster, subsessile; pedicel up to 3.0 mm long; bract ± 1.0 mm long, linear. Flowers bright yellow, 9.0 — 11.0 mm long. Calyx 3.0 — 4.0 mm, yellow-green, villous; tube 2.0 — 2.5 mm; dorsal teeth triangular, 1.0 — 1.5 mm, fused for less than one third of lobe length; ventral teeth triangular, 1.0 — 1.5 mm, fused for about two thirds of lobe length, spreading, apex acute. Standard 10.0 — 12.5 mm long; claw linear, 3.0 — 4.0 mm long, lamina broadly ovate, 8.0 — 11.0 X 10.0 — 13.5 mm, apex emarginate, base cordate, back of standard sericeous, glabrous only along edge. Wing petals 9.0 — 11.0 mm long, equal to slightly longer than keel, claw 3.0 — 4.0 mm long, lamina obliquely oblong, 8.0 — 9.0 X 4.0 — 4.8 mm, shortly pilose along midrib to glabrous, apex truncate, base rounded auriculate, lunulate and rectangular depression with lamellate sculpturing. Keel petals 8.0 — 10.0 mm long, claw 3.5 — 5.0 mm long, lamina oblong-elliptical, 6.5 — 7.5 X 3.5 — 4.5 mm, pilose along fore edge, apex obtuse, base rounded-auriculate. Stamens basifixed anthers 1.3 — 1.4 mm long, carinal anther 1.0 — 1.2 mm long, dorsifixed anthers 0.7 — 0.8 mm long; staminal tube 6.9 — 8.0 mm long, unfused portion spreading, loosely arranged around style. Pistil 8.2 — 9.2 mm long; ovary 5.7 — 6.3 X 0.9 — 1.2 mm, ovules 9 — 11; style usually at 70 — 80̊ angle, height of curvature 2.1 — 2.5 mm, glabrous, except basally. Fruit indehiscent, partially plicate, straight to slightly falcate, sericeous, pale olive-green, 17.0 — 29.0 X 3.0 — 4.0 mm. Seed ovate-reniform, testa olive-green to dark-brown, smooth, 1.9 — 2.7 mm X 1.8 — 2.4 mm, 1.6 — 2.1 mm thick.

Etymology

The specific epithet honours Prof. Charles Howard Stirton for his extensive work on Cape legumes and his late wife, Dr Jana Stirton (Born Zantovska) who shared his love and passion for the diversity and conservation of the Overberg Renosterveld. They assisted in the formation of the Overberg Renosterveld Conservation Trust and establishment of the Haarwegskloof Private Nature Reserve and research centre. Prof. Stirton has significantly mentored the first author in his development as botanist.

Diagnostic characters

Polhillia stirtoniana was previously circumscribed as part of P. pallens , but is distinguished from P. pallens species by its very narrow, arcuate leaflets that are not wider than 1.0 mm (versus at least 1.0 — 3.0 mm wide); dense terminal burst branching forming a closed, umbrella like canopy, rendering the plant wider than its height (versus shrub not forming closed canopy); and fruit that are weakly plicate (versus fruit not plicate).

Distribution, ecology and conservation status

Polhillia stirtoniana flowers from June to September. It often grows abundantly in sheltered gullies and cooler southern slopes in Eastern and Central Ruens ^Shale Renosterveld (FRs 12 & FRs 13) ( Mucina and Rutherford, 2006). The species is distributed from Potberg in the east to the R 319 in the west with an outpost at Stormsvlei further north ( Fig. 6B ). It is the most abundant of all Polhillia species. This may be due to being protected from ploughing, as it prefers steep slopes and deep gullies and is often the dominant species in these habitats. The species, however, remains threatened by fragmentation throughout its distribution range and some sub-populations have been lost to recent ploughing. At present, this species is known from 12 extant locations, and more may be found as other areas of the Overberg are explored. The Red Data List status of this species is proposed as Near Threatened (NT A2c; B 1ab(iii,iv,v)+ B 2(iii,iv,v)) following the latest IUCN categories and criteria ( IUCN, 2012).

Additional specimens

3420 (Bredasdorp): Witkop, 15 km ESE of Stormsvlei (— AA), 1 Oct 1983, C.J. Burgers 3212 (K, NBG); Top of Stormsvleikloof (— AA), 4 Jul 1987, B.- E. van Wyk 2706 (JRAU); Farm Uitvlugt (— AC), 11 Jul 2018, B. du Preez 517 (BOL, PRE); Koppies on farm Uitkyk (— AC), 11 Jul 2018, B. du Preez 518 (BOL); Near Remhoogte, north of Bredasdorp (— AC), 9 Oct 1986, B.- E. van Wyk 2095 , 2096 (JRAU); Goereesoe farm next to R319 (— AC), 10 Aug 2017, B. du Preez 313 (BOL, PRE); Goereesoe farm, Bredasdorp region (— AC), 26 Nov 2011, Muasya, Stirton & Curtis 6303 (BOL); 10 Sept 2011, Curtis 15 (BOL); Plaatjieskraal (— AC), 7 Dec 2011, Muasya, Stirton & Curtis 6349 (BOL); Luipaardskop farm at northern foothills of Suikerkankop (— AD), 2 Oct 1983, C.J. Burgers 3197 (NBG); Farm Luipaardskop 53, about 12 km NW of Wydgelee (— AD), 10 Sept 2000, Helme 1760 (NBG), 2 Oct 1983, C.J. Burgers 3197 (K, NBG); Luipaardskop farm, north of Haarwegskloof along road (— AD), 12 Sept 2017, B. du Preez 341 (BOL); Spitskop (east) farm near planted Eucalyptus trees (— AD), 20 May 2017, B. du Preez 281 (BOL); Haarwegskloof, north of research centre (— AD), 6 Aug 2017, B. du Preez 308 (NBG); Bredasdorp, Haarwegskloof farm (— AD), 12 Oct 2011, Stirton , Ibrahim & Curtis 13362 (BOL); Haarwegskloof Nature Reserve (— AD), 8 Oct 2014, Stirton 14059 (BOL); Nysty Farm, 40 km north of Bredasdorp, along San Souci road (— AD), 2 Dec 2011, Stirton & Curtis 13442 (BOL); Farm Spitskop, near Ouplaas (— AD), 25 Sept 1986, J. Albertyn 852 (NBG); 33 km NE of Bredasdorp on Plaatjieskraal farm (— AD), 1 Aug 2001, Helme 2061 (NBG); Potberg Nature Reserve, 1.5 km due west of Potberg Education Centre (— BC), 1 Sept 1983, C.J. Burgers 3129 (K, NBG); 1 km west of Potberg centre, De Hoop (— BC), 10 Oct 1986, B.- E. van Wyk 2128 (JRAU); Potberg Nature Reserve, 50 m from western perimeter fence up gulley (— BC), 11 Jul 2018, B. du Preez 516 (BOL).

Figures

Fig. 19. Composite plate of Polhillia stirtoniana. 1 — Flower front view; 2 — Flower side view; 3 — Flower bottom view; 4 — Wing petal; 5 — Keel petal; 6 — Androecium; 7 — Gynoecium; 8 — Fruit;9 — Close-up of recurved leaves and stipules; 10 — Habit. Scale bars: 4 mm. Photographs by B. du Preez

Fig. 6. Map showing distribution of Polhillia in the Western Cape Province, South Africa.A — Distribution of extra Overberg species; B — Species within and just outside of the Overberg region. Note expansion of square in A to map in B.