Acanthopsis dregeana H.M.Steyn, 2016

Steyn, Hester M. & Van Wyk, Abraham E., 2016, Taxonomic notes on the shrublet species of Acanthopsis (Acanthaceae, tribe Acantheae), with two new species from South Africa, Phytotaxa 244 (2), pp. 145-160 : 155-158

4. Acanthopsis dregeana H.M.Steyn , sp.nov. ( Figs. 1 , 3D , 6 & 7D, d )

Acanthopsis dregeana differs from all other shrublet members of Acanthopsis in having middle to upper floral bracts ending in 3 ovate, mucronate to spinose lobes (vs. ending in 5(–7) drawn-out primary spines), middle to upper bracts with long, glandular hairs (vs. subsessile glandular hairs—when present) and a lemon-yellow (vs. white) corolla throat.

Type: — SOUTH AFRICA. Northern Cape: Namaqualand District, NW of Eksteenfontein, (2817CA), 16 September 2010, Steyn 1822 (holotype PRE0861475 -0!; isotype NBG!) .

Perennial shrublet, 15–40 cm tall. Stems brown (maroon when young), ribbed, almost glabrous to hirsute with deflexed short, white hairs; internodes (10–) 15–30 mm long. Leaves lanceolate to oblanceolate, 25–45(–50) × 7–10(–12) mm, appears glaucous with appressed, densely packed short hairs; margin undulate, coarsely dentate-spinose, spines rigid, 2–4 mm long, orange-brown; base attenuate, decurrent. Inflorescences cylindrical, clearly pedunculate, with 2 or 3 pairs of peduncular bracts; 30–55 mm long (excluding peduncle), 10–12 mm in diameter, peduncle (14–)20–40(–70) mm long, pubescent with short, spreading hairs. Bracts obovate to oblong, 18–24 mm long, base 10–13 mm long; lower bracts ending in 3(–5) primary spines, central primary spine always simple and recurved; middle to upper bracts oblong, 5 primary veins converging into 3 mucronate to spinose, ovate lobes with 2 outer lobes reduced, central primary spine always simple, spine tips often dark brown or maroon; peduncular bracts strigose with appressed, short hairs, lower fertile bracts strigose with appressed short hairs becoming more densely pubescent with long, glandular hairs towards the top of inflorescence. Bracteoles linear to sickle-shaped, unequal in length, 3–6 mm long; silky hairy, also with glandular hairs. Calyx with dorsal sepal oblong, acuminate, 10–11 mm long, silky hairy especially adaxially, also with short spreading and glandular hairs abaxially, 7–9-veined from base; ventral sepal ovate, 10–11 mm long, silky hairy especially adaxially, also with short spreading and glandular hairs abaxially, 5–7-veined from base; lateral sepals lanceolate, ending in spinous tip, broader at base, 8 mm long, silky hairy especially along margins, also with isolated glandular hairs. Flowers lilac to purple with lemon-yellow throat; corolla 23–25 × 8–10 mm, tube 7(–8) mm long, pubescent; central lobe usually longer than wide, constricted at base, truncate. Stamens with brown anthers, 3 mm long; filaments 5–6 mm long, glandular. Style with patch or ring of glandular hairs at base. Capsules narrowly ovate, flattened, glabrous, shiny, 7 × 2 mm, 2-seeded. Seeds 5 × 3 mm, covered with long white hygroscopic hairs.

Eponymy: —Named after Johann Fran(t)z Drège (1794–1881), horticulturalist, botanical collector and traveller, who collected most of the Acanthopsis type specimens. Drège collected about 200 000 specimens (representing ca. 8 000 species) in South Africa between 1826–1834 ( Glen & Germishuizen 2010).

Distribution, ecology and phenology: — Acanthopsis dregeana is endemic to South Africa, and only known from two localities north-west of Eksteenfontein, Northern Cape ( Fig. 1 ). It is centred in the core part of the Gariep Centre of Endemism ( Van Wyk & Smith 2001), this distribution falls within the Succulent Karoo Biome ( Rutherford & Westfall 1994, Low & Rebelo 1996, Mucina & Rutherford 2006) and within the Central Richtersveld Mountain Shrubland (SKr 1) vegetation type ( Mucina & Rutherford 2006). The mean annual rainfall in this area is 50–100 mm, received mainly in winter. The specimens were collected at elevations of 400–440 m on hill slopes in well-drained sandy loam, stony soils. Flowering time: August and September.

Notes: —Plants observed in nature were heavily grazed and most of the fruit were parasitized, apparently by insects.

Conservation status: — Acanthopsis dregeana is only known from two sublocalities in the vicinity of Eksteenfontein, an area where severe overgrazing and trampling by domestic livestock are causing continuing loss and degradation of the habitat. Should grazing pressure continue to increase, the population is potentially at risk. The species therefore qualifies for Critically Endangered B1ab(iii,v) ( IUCN 2001) (L. von Staden, pers. comm. 2015).

Additional specimens examined: — SOUTH AFRICA. Northern Cape: Namaqualand District, 19 km NW of Eksteenfontein on road to Khubus, (2817CA), 23 August 2012, Steyn 1886 (PRE!).

Figures

FIGURE 1. Known distribution of the shrublet species of Acanthopsis: A. spathularis (○), A. horrida (●), A. erosa (■) and A. dregeana (▲).

FIGURE 3. Comparison of floral parts in shrublet species of Acanthopsis (from left to right): bract(s), bracteoles, calyx (4 sepals: dorsal, ventral and 2 lateral ones) and flower. A. A. spathularis, B. A. horrida, C. A. erosa, D. A. dregeana. Note: the bract on the left is from lower down in the same inflorescence. Scale bar = 10 mm. Vouchers:A = Steyn 2135 (PRE), B = Koekemoer 4397 (PRE), C = Steyn 1874 (PRE), D = Steyn 1822 (PRE).

FIGURE 6. Scanned image of holotype of Acanthopsis dregeana H.M.Steyn (Steyn 1822, PRE).

FIGURE 7. Habit and flowers of A, A. spathularis, B. A. horrida, C. A. erosa, D. A. dregeana. Photographs: H.M. Steyn (A, a, B), M. Koekemoer (b, C, d), S.P. Bester (c, D).