Acanthopsis glauca (Nees) Schinz (1890: 201)

Steyn, Hester M. & Van Wyk, Abraham E., 2017, Taxonomic notes on Acanthopsis Harv. (Acanthaceae, tribe Acantheae): the group with trifid bracts, Phytotaxa 295 (3), pp. 201-217 : 203-209

1. Acanthopsis glauca (Nees) Schinz (1890: 201) ; ( Figs. 1 , 2A, B , 4A , 5 )

Clarke (1901: 34). Acanthus glaucus E.Mey. in Drège (1843: 91, 161), nom. nud. Acanthus glaucescens E.Mey. in Drège (1843: 95), nom. nud. Acanthodium glaucum Nees von Esenbeck (1847: 277) . Blepharis glauca (Nees) Anderson (1864: 36) .

Type: — SOUTH AFRICA. Northern Cape: [Illegible] zum Goedemanskraal & Kaus, 2500–3000 ft [760–915 m], 8 September 1830, Drège 2434 (lectotype P04426154 scan! designated here).

Perennial subshrub, 15–20 cm tall. Leaves sessile; lamina oblanceolate, (40–)55–70(–80) × (5–)7–8(–10) mm, glaucous with appressed, densely packed short hairs; base attenuate; margin undulate, coarsely dentate-spinose, spines rigid, (2–)3–5(–7) mm long, yellowish brown or maroon; apex acute to cuspidate. Inflorescences pedunculated, cylindrical to slightly turbinate in fruit, (35–)50–75(–90) mm long (excluding peduncle), 8–10 mm in diameter; peduncle usually 15–30(–50) mm long, with 2 or 3 pairs of peduncular bracts, pubescent with deflexed short, white hairs. Bracts oblong to obovate, coriaceous, (22–) 25–35 mm long, lamina 12–18 mm long; lower bracts ending in 3(–5) primary spines, central primary spine always simple and recurved, usually more than twice the length (up to 30 mm) of lateral spines; middle to upper bracts oblong, nearly always with 3 primary spines (when 5, then outer spines very reduced), central primary spines nearly always simple, 5 primary veins very often converging into 3 attenuate spines, central primary spine nearly always with excurrent tip, twice as long (up to 20 mm) as lateral spines, spreading; spines and venation often maroonish, puberulent to hirsute with deflexed or spreading, short hairs, often with long, silky hairs abaxially towards the base and short glandular hairs adaxially. Bracteoles linear, 5 mm long, silky-hairy. Calyx with dorsal sepal ovate, acuminate, 11–13 mm long, silky-hairy, 5–7-veined from the base; ventral sepal ovate, 10–11 mm long, silky-hairy, 5–7-veined from the base; lateral sepals lanceolate, ending in spinous tip, broader at the base, 8–9 mm long, silky-hairy. Corolla lilac to white with dark purple veins and lemon-yellow throat, 27–30 × 11–13 mm long, tube 9–10 mm long; central lobe usually wider than long, constricted at base, truncate. Filaments 7–8 mm long, glandular; anthers orange-brown, 3 mm long. Style with patch of glandular hairs at base. Capsules ovate, flattened, glabrous, shiny, 7 × 3–4 mm. Seeds ovate, 4 × 2 mm, covered with long white hygroscopic hairs.

Etymology: —The specific epithet “ glauca ” refers to the glaucous appearance of the plants due to an indumentum of densely packed, appressed, short hairs.

Distribution, ecology and phenology: — Acanthopsis glauca is restricted to the mountainous areas to the south and east of Lekkersing ( Fig. 1 ), Northern Cape, at elevations between 300– 550 m. This area falls within the Gariep Centre of Endemism ( Van Wyk & Smith 2001) and in the Succulent Karoo of Rutherford & Westfall (1994), Low & Rebelo (1996) and Mucina & Rutherford (2006). This species is usually associated with fields of white quartz pebbles and prefers shallow, sandy loam soil in Die Plate Succulent Shrubland (SKr 10) and Central Richtersveld Mountain Shrubland (SKr 1) vegetation types ( Mucina & Rutherford 2006). Fog is common in Skr1 but of little importance in SKr 10, with the mean annual rainfall between 50–100 mm, but usually less than 90 mm. Specimens with flowers were collected from August to October.

Notes: —The authorship of the name Acanthopsis glauca was incorrectly attributed to “(E.Mey.) Schinz” by some authors (e.g. Welman 2003; Snijman 2013). Although Acanthus glaucus was first applied by Meyer in Drège (1843) to a Drège collection, it was invalidly published because no description was provided. Nees von Esenbeck (1847) validly published the name Acanthodium glaucum by citing Acanthus glaucus as a synonym. The authorship of the name Acanthopsis glauca is therefore either “(E.Mey. ex Nees) Schinz” or “(Nees) Schinz”.

Although the four specimens of Drège's collection were all labelled Acanthus glaucus or Acanthopsis glauca , the material on the sheets Drège 2434 (P04426154) and Drège s.n. (GZU000250678) differs from the other two in having a more ‘closed’ inflorescence with much shorter, less spreading spines on the bracts. The latter is, however, considered to be a young inflorescence of the same taxon. Specimens with similar young inflorescences include: Oliver, Tölken & Venter 803 and some inflorescences on Steyn 1857, 2143. There are currently four sheets known in Drège's collections ( Drège 1843) collected on at least two different dates and localities, namely Drège s.n. (19 August 1830 (P)), Drège 2434 (8 September 1830 (P)), Drège 2435 (September 1830 (S-G)) and Drège s.n. (no date (GZU)). The Paris specimen (Drège 2434) was selected as lectotype as it is annotated with the collector number, date and locality in Drège's handwriting.

Conservation status: — Acanthopsis glauca has a very limited distribution range and is known from three small subpopulations. Its entire known range falls within communally owned rangelands that are overstocked with livestock, and severely degraded due to overgrazing and erosion, particularly in the lowlands close to settlements. Although this taxon is not browsed, field observations indicate habitat degradation due to trampling by cattle at one of the subpopulations. Because of its localized distribution and potential threat of habitat degradation due to overgrazing and trampling, it meets the criterion D2 for the category Vulnerable according to the IUCN Red List Category and Criteria ( IUCN 2001) (L. von Staden, pers. comm.).

Additional specimens examined: — SOUTH AFRICA. Northern Cape: Richtersveld, Lekkersing, Karuchabpoort , 9 km South of Lekkersing main hills North of poort, 350 m, (2917 AA), 8 September 1977, Oliver, Tölken & Venter 803 ( PRE) ; Namaqualand District, 8 km S of Lekkersing, Karuchabpoort , 346 m, (2917 AA), 10 August 2011, Steyn 1857 ( PRE) ; Namaqualand District , S of Lekkersing, 298 m, (2917 AA), 11 October 2015, Steyn 2143 ( PRE) ; Namaqualand District, on road between Eksteenfontein & Lekkersing , 549 m, (2817 CC), 24 August 2012, Steyn 1888 ( PRE) ; Namaqualand District , between Lekkersing and Eksteenfontein, 556 m, (2817 CC), 11 October 2015, Steyn 2146 ( PRE). Without precise locality: [Illegible] Kasparskloof, 2000–3000 ft [610–915 m], III C, 19 August 1830, Drège s.n. (P04426152) ; no locality or date, Drège s.n. ( GZU000250578 scan) ; Klein Namaqualand , Inter Olifantsrivier & Kaus, in montibus, September 1830, Drège 2435 (S-G-44 scan) .

Figures

FIGURE 1. Distribution of Acanthopsis taxa within the trifid bract group: A.dregeana subsp. dregeana (●), A. dregeana subsp. longispina (○), A. tetragona subsp. tetragona (■), A. tetragona subsp. pedunculata (□) and A. glauca (▲).

FIGURE 2. Comparison of habit and flowers in members of Acanthopsis with trifid bracts. A, B. A. glauca, C, D. A. dregeana subsp. dregeana, E, F. A. dregeana subsp. longispina. Photographed by: H.M. Steyn (A, C, D, E) and M. Koekemoer (B, F).

FIGURE 4. Comparison of floral parts in members of Acanthopsis with trifid bracts (from left to right): bract(s), bracteoles, calyx (4 sepals: dorsal, ventral and 2 lateral ones) and corolla with anthers. A. A. glauca, B. A. dregeana subsp. dregeana, C. A. dregeana subsp. longispina, D. A. tetragona subsp. tetragona, E. A. tetragona subsp. pedunculata. Note: the bract on the left is from lower down in the same inflorescence. Scale bar = 10 mm. Vouchers:A = Steyn 1888 (PRE), B = Steyn 1822 (PRE), C = Steyn 2141 (PRE), D = Steyn 1848 (PRE), E = Steyn 2144 (PRE).

FIGURE 5. Acanthopsis glauca. A & B. Habit. C & D. Leaf indumentum (abaxial). E & F. Bract.G. Calyx. H. Corolla lobes lilac to white, throat lemon-yellow. I. Glandular hairs at base of style. J. Capsule. K. Seed. Vouchers: C–H = Steyn 2146 (PRE), I–K = Steyn 1888 (PRE). Photographed by: M. Koekemoer (A, B) and H.M. Steyn (C–K).