Stenostelma urceolatum Bester & Nicholas, 2018

Bester, Stoffel P. & Nicholas, Ashley, 2018, New combinations in Stenostelma (Apocynaceae-Asclepiadoideae) and two novel species from South Africa, Phytotaxa 361 (1), pp. 41-55 : 49-50

Stenostelma urceolatum Bester & Nicholas spec. nov.

Closely related to Stenostelma corniculatum from which it differs in the shorter extended corona lobe without lateral expanded wings and in the elongated gynostegial column.

Type:— SOUTH AFRICA, KwaZulu-Natal, 2730 (–DD), Vryheid District, ± 7.8 km S from Vryheid, Klipspruit dam, slope below dam wall, alt. 1088 m, 10 February 2006 (fl.), S.P. Bester 6541 (holotype, PRE!; isotypes, K!, MO!, NH!). ( Fig. 8A ). ( Fig. 5–8 ) .

Geophytic herb 145–450 mm tall, all parts with milky latex ( Fig. 7A ). Stems usually solitary, otherwise branched from neck; neck 60 mm long; tuber 56 × 15 mm; older stems sparsely pilose to villous and pronouncedly terete. Leaves opposite, sessile or petiolate then <5 mm long, narrowly lanceolate to lanceolate, 13–125 × 2–5 mm, base attenuate, apex apiculate, margin revolute, distinct midvein much paler, much longer than internodes; glabrous. Peduncle short, inflorescences appearing sessile but peduncle 1–3.5 mm long (12–19 mm long in fruit), sparsely pilose; pedicel 1–4(– 5 mm long in fruit), sparsely pilose. Inflorescence axillary, umbellate, 3–8 per stem, 4–10-flowered; bracts linear to filiform, 2.2–3.0 mm long, apex acute, sparsely pilose towards the base and centre below ( Fig. 7C ). Calyx narrowly deltate, 3.2–4.7 × 1.2–1.4 mm, apex acute, sparsely pilose towards the base and centre below. Flowers pseudo-urceolate, 4.5–7.1 × 3.9–5.8 mm (recurved apical tips excluded, these 1.12 mm long), segments fused for lower 0.9–1.5 mm (lower fifth), upper 3–4 mm free but tightly joined below; segments ovate, 2.5–2.7 × 1.6–2.0 mm, green on the outside and whitish-pink on the inside. Corona lobes 3.9–6.3 × 1.5–2.2 × 0.8–1.0 with stype in ± lower fifth, lower half ovate dilating into thin apical extension half the length of the full lobe; outer margin convex with appendix inwardly directed, inner margin concave ( Fig. 6D, 6G ), upper half abruptly extended into narrow tip. Basal flaps 0.32 mm long. Gynostegial column 5.26 mm tall, gynostegial head 1.1–2.3 × 1.6–2.3 mm, ±half the length of the gynostegial column. Anthers 1.1–1.9 × 0.6–1.1 mm; anther appendages ovate, 1.18–1.64 × 0.80–1.1, apex acute to rounded; anther-wings 1.32–2.71 × 0.33–0.52 mm, notched ± third from base. Pollinarium: pollinia ± unevenly deltoid narrower at apex where attached to caudicle, 0.584 –1.318 × 0.255 –0.607 mm, inner-margin straight, outer-margin rounded; caudicle 0.198 –0.498 × 0.103 –0.113 mm, lower end attached to pollinia; corpuscle narrowly ovate, 0.318 –0.747 × 0.086 –0.209 (0.223 –0.498) mm with horn included and with lateral horn 82–147 μm; upper end attached to corpuscle, winged and 0.151 –0.181 mm broad and flattened. Fruit 41–91 × 5–7 mm, longitudinally striped in two shades of green, sparsely pilose. Seed not seen.

Habitat:—Growing in gently undulating grasslands and hill slopes on NW aspects and pan/depression in well-drained stony to rocky and clayey soil, in full sun. One label stated the lithology to be dolerite. The known habitat has been indicated on specimen labels to include the: Sub-Escarpment Grassland Bioregion within the Income Sandy Grassland vegetation unit ( Mucina et al. 2006); and North-Eastern Mountain Grassland ( Bredenkamp et al. 1996).

Distribution:— Stenostelma urceolatum is known only from northern KwaZulu-Natal in the Newcastle and Vryheid districts ( Fig. 5 ).

Phenology:—All specimens were collected in February, mostly in flower, but also the fruiting specimens dated from this month. It is deduced from the current material available that the plants flower quickly and have a short flowering period with fruit produced within a couple of weeks after flowering.

Etymology:—The specific epithet is in reference to the shape of the corolla which is urceolate.

Conservation assessment:—This species has been recorded from 3 locations within an EOO of 1035 km 2 (EOO <5000 km 2). The Vryheid and Newcastle locations are ± 98 km apart and the two Vryheid sub-populations ± 22 km apart. Therefore, there are three known sub-populations in three locations. The one sub-population at Vryheid is in a conservation area and the other in an area used for livestock farming. The third sub-population, at Newcastle, is also on a farm. It is unlikely that these populations are undergoing a continual decline and no current threats to their existence is foreseen. This species is thus assessed as Least Concern (LC) but Rare according to Victor & Keith (2004) (Assessors: S.P. Bester & J.E. Victor 17/02/2016).

Summary of criteria met:

• 3 locations, no continuing decline

• EOO= 1035 km 2

• LC, Rare

Specimens examined:— SOUTH AFRICA. KwaZulu-Natal. Vryheid (2730): (–DD) Vryheid District, ± 7.8 km S from Vryheid , Klipspruit dam, hillslope S of dam wall, Klipfontein 316 farm, alt. 1106 m, 15 February 2010 (fr.), S.P. Bester 9845 ( PRE! with fruit only) ; alt. 1088 m, 7 Feb. 2013 (fr.), S.P. Bester 11500 ( PRE! with immature fruit only) ; alt. 1101 m, 22 February 2012, S.P. Bester 11080 ( PRE! with fruit remains only. (–BB), 20 km from Vryheid towards Nongoma, alt. 1136 m, 9 February 2006 (fl.), S.P. Bester 6517 ( NH!, NU!, PRE!). Volksrust (2729): (–DB) Newcastle District , Rotsvas, Ingogo, 16 February 2002 (fl.), F. & S.J. Siebert 1940 ( PRE!) .

Figures

FIGURE 6. Stenostelma urceolatum. A, Habit. B, Tuber. C, Flowers side view. D, Flower side view with calyx, corolla lobes and corona lobes removed. E, Flower vertical view. F, Pollinarium.G–I, Corona lobe; G, side view; H, dorsal view; I, ventral view. J, Fruit. Scale bars: A, B, J, 10 mm; C, 1 mm; D, 1 mm; E, 0.5 mm; F, 0.2 mm; G–I, 0.5 mm. Voucher: Bester 6541 (PRE). Artist: G.S. Condy.

FIGURE 8. Scan of holotype of Stenostelma urceolatum, Bester 6541 (PRE).

FIGURE 5. Known distribution of Stenostelma ligulatum (z) and Stenostelma urceolatum („).Map created in ArcGIS10.1.

FIGURE 7. Stenostelma urceolatum: A, Habit. B, Inflorescence close-up. Stenostelma periglossoides: C. Stenostelma carinatum: D. Stenostelma corniculatum: E. Scale bars: A, C, E, 10 mm; B, D, 5 mm.. Photos: S.P. Bester.