Acanthopsis erosa 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

3. Acanthopsis erosa H.M.Steyn , sp. nov. ( Figs. 1 , 3C , 5 & 7C, c )

Acanthopsis erosa differs from A. dregeana in having middle to upper floral bracts ending in 5 drawn-out primary spines (vs. ending in 3 ovate, mucronate to spinose lobes) and the corolla throat being white (vs. lemon-yellow) and from all other shrublet members of Acanthopsis in having dentate-spinose to erose leaf margins (vs. coarsely dentate-spinose) and inflorescences 50–80(–100) mm long (vs. (14–)20–60(–70) mm long).

Type: — SOUTH AFRICA. Northern Cape: Calvinia District, SW of Kaggakammaskloof, (3219DA), 20 August 2011, Steyn 1874 (holotype PRE0861469 !; isotype KMG!) .

Perennial shrublet, 20–30 cm tall. Stems brown, ribbed, pubescent with white, spreading hairs; internodes 8–10 mm long. Leaves lanceolate, 40–45(–55) × 4–6 mm, appear glaucous, strigose with densely packed, short hairs, also with scattered subsessile glandular hairs; margin undulate, dentate-spinose to erose, spines fine 1–2 mm long, yellow; base attenuate, decurrent. Inflorescences cylindrical, subsessile to pedunculate with 2 (or 3) pairs of peduncular bracts; 50– 80(–100) mm long (excluding peduncle), 8–10 mm in diameter, peduncle (5–)10–15(–20) mm long, pubescent with short, spreading hairs. Bracts wedge-shaped, 15–20 mm long, base 4–7 mm long; ending in 5 primary spines, central primary spine usually simple, occasionally with 1 (or 2) pairs of marginal secondary spines, lateral spines usually with 1 long, basal secondary spine (usually as long or longer than primary spines) and 1 short, marginal secondary spine; hirsute to velvety with deflexed to spreading short hairs, occasionally also with subsessile glandular hairs. Bracteoles linear, 7–9 mm long, silky hairy. Calyx with dorsal sepal ovate, attenuate, 13 mm long, silky hairy especially adaxially, often short, spreading hairs abaxially, 7–9-veined from base; ventral sepal ovate, 10–12 mm long, silky hairy especially adaxially, often with short, spreading hairs abaxially, 5–7-veined from base; lateral sepals lanceolate, ending in spinous tip, broader at base, 9 mm long, silky hairy especially along margins. Flowers lilac to purple with darker veins and white throat; corolla 28 × 12 mm, tube 8–10 mm long, pubescent; corolla limb recurved, central lobe usually wider than long, constricted at base, truncate to emarginate. Stamens with purple-black anthers, 2 mm long; filaments 7(–8) mm long, glandular, hairy towards the base. Style with patch of glandular hairs at base. Capsules ovate, flattened, glabrous, shiny, 7 × 4 mm, 2-seeded. Seeds 4 × 4 mm, covered with long white hygroscopic hairs.

Etymology: —The specific epithet, erosa (the Latin meaning “irregularly toothed, appearing as if nibbled”), refers to the leaf margins of this species.

Distribution, ecology and phenology: — Acanthopsis erosa is endemic to South Africa, only known from the type locality near the border of the Northern and Western Cape ( Fig. 1 ). The distribution of A. erosa falls within the Swartruggens Quartzite Karoo (SKv2) vegetation type in the Rainshadow Valley Karoo Bioregion ( Mucina & Rutherford 2006), within the Succulent Karoo Biome ( Rutherford & Westfall 1994, Low & Rebelo 1996, Mucina & Rutherford 2006). This species is found at an elevation of 500 m and is associated with deep sandy soils and grows in an area receiving a mean annual rainfall (mainly in winter) of 100–150 mm. Flowering time: August.

Conservation status: — Acanthopsis erosa is currently only known from the type locality and is possibly a Swartruggens Quartzite Karoo endemic with a limited distribution range. However, this area is botanically underexplored and more populations can be expected in suitable habitats. As the population is currently not exposed to any potential threat, a preliminary status of Rare ( Raimondo et al. 2009) is assigned to this species (L. von Staden, pers. comm. 2015).

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 5. Scanned image of holotype of Acanthopsis erosa H.M.Steyn (Steyn 1874, 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).