Acanthopsis insueta H.M.Steyn, 2017

Steyn, Hester M. & Van Wyk, Abraham E., 2017, Taxonomic notes on Acanthopsis (Acanthaceae, tribe Acantheae): the group with semi-dense spikes and 5 - fid bracts, Phytotaxa 324 (2), pp. 101-121 : 115-117

5. Acanthopsis insueta H.M.Steyn , sp. nov. ( Figs. 1 , 3E & 8 )

Type: — SOUTH AFRICA. Northern Cape: Namaqualand District. Richtersveld National Park . Vyftienmylberg ; on track to top of mountain, 292 m, (2917 AA), 7 September 2010, Steyn 1805, (holotype PRE0861485 !; isotype NBG!) .

Diagnosis: — Acanthopsis insueta differs from A. glandulopalmata in having middle to upper bracts ending in (3–)5 ensiform or narrowly winged primary spines (not 5 winged primary spines) and the lateral spines usually with a basal secondary spine on the side facing the central primary spine (not lateral spines always simple) and from A. carduifolia in having grey leaves with appressed hairs (not green leaves with strigose hairs) and bracts with secondary spines often longer than primary spines (not secondary spines always shorter than primary spines) and a lemon-yellow (not cream or white) corolla throat.

Perennial, compact subshrub, 15 cm tall with very short internodes. Leaves sessile, decurrent, base petiole-like with spines 3–6 mm long; lamina oblanceolate, (25–)35–50(–70) × 8–10(–12) mm, grey with appressed, densely packed short hairs; apex acute, base attenuate, margin undulate, dentate-spinose to coarsely dentate-spinose, spines rigid, 4–7(–8) mm long, yellow to dark brown. Inflorescences semi-dense, cylindrical, subsessile, ca. 35–45 mm long, 8– 10(–12) mm in diameter. Bracts obovate to wedge-shaped, 11–13 mm long (including spines), lamina 5–8 mm long; spines and lamina pubescent to hirsute with deflexed to spreading short hairs, lamina often with isolated long white hairs abaxially, silky-hairy adaxially; lower bracts ending in 5 primary spines; middle and upper bracts ending in (3–)5 primary spines, upper bracts very often 3-fid (see Figs. 3 & 8 ); central primary spine usually simple or with short marginal secondary spines; lateral primary spines usually with long basal secondary spine on side facing central primary spine, often longer than primary spines; spines spreading to recurved in fruit;. Bracteoles linear, 4–5(–6) mm long, silky-hairy. Calyx with dorsal sepal ovate, acuminate, 11–12 mm long, silky-hairy especially abaxially, 7–9- veined; ventral sepal ovate, 9–11 mm long, silky-hairy especially abaxially, 5–7-veined; lateral sepals 9 mm long, silky-hairy. Corolla lilac to purple with lemon-yellow throat, 25 × 10 mm, tube 9 mm long, central lobe wider than long, constricted at base, emarginate. Filaments 6 mm long, glandular; anthers beige to orange-brown, 3 mm long. Style with patch of glandular hairs at the base. Capsules 8 × 3–4 mm. Seed 5 × 3 mm.

Etymology: —The specific epithet insueta , meaning “unusual”, refers to the unusual combination of middle to upper floral bracts ending in 3 or 5 primary spines.

Distribution, ecology and phenology: — Acanthopsis insueta is endemic to the Vyftienmylberg (Northern Cape) and is known from two localities ( 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). It is found in the Richtersveld Bioregion, Vyftienmyl se Berge Succulent Shrubland ( Mucina & Rutherford 2006) where it receives predominantly winter rains with an average of 60–120 mm per year (including considerable amounts of fog). The specimens were collected on mountain slopes associated with quartzite stones in well-drained, sandy soils at elevations between 230 and 445 m. Specimens with flowers were collected in August (probably also flowers into September).

Conservation status: — Acanthopsis insueta is a highly localized Richtersveld endemic (EOO <10 km ²). This species is known from a small area on the northern section of the summit of Vyftienmyl-se-Berg, an inselberg that is home to many local endemics. As there are no severe threats, the population is not likely to be declining. As its habitat is well-protected and the species is not in danger of extinction, it is given a status of Critically Rare (L. von Staden, pers. comm.).

Additional specimen examined (Paratype): — SOUTH AFRICA. Northern Cape: Namaqualand District. Richtersveld National Park . Vyftienmylberg ; top of mountain, 444 m, (2917 AA), 9 September 2010, Steyn 1806 ( PRE!) .

Notes: —In the case where Acanthopsis insueta has trifid bracts, it differs from A. glauca in having sessile inflorescences and bracts with primary spines of approximately the same length (not pedunculate inflorescences and bracts with central primary spine much longer than lateral spines) and from all other species with trifid bracts in having ensiform spines (not ovate, mucronate to spinose lobes).

Figures

FIGURE 1. Known distribution of A. glabra (○), A. scullyi (▲), A. nitida (□), A. glandulopalmata (■) A. insueta (Δ) and A. carduifolia (●). Thunberg’s route (1774) indicated in red. (for explanation see Notes under taxonomic treatment of A. carduifolia)

FIGURE 3. Comparison of floral parts, associated bracts and bracteoles (from left to right): bracts (2), bracteoles (2), calyx (4 sepals: dorsal, ventral and 2 lateral ones) and corolla with anthers.A. A. glabra, B. A. scullyi, C. A. nitida, D. A. glandulopalmata, E. A. insueta, F. A. carduifolia. Note: the bract on the left is from lower down in the same inflorescence. Scale bar = 10 mm. Vouchers:A = Steyn 1893 (PRE), B = Steyn 1911 (PRE), C = Steyn 1884 (PRE), D = Steyn 1890 (PRE), E = Steyn 1805 (PRE), F = Koekemoer 4620 (PRE).

FIGURE 8. Acanthopsis insuenta. A & B. Habit. C & D. Leaf indumentum (abaxial). E & F. E &F. Bract. G. Calyx. H. Corolla (lobes lilac; throat lemon-yellow). I. Glandular hairs at base of style. J. Capsule. K. Capsule with seed. Vouchers: C–K = Steyn 1805 (PRE). Photographed by: H.M. Steyn (A–K).