Acanthopsis tuba H.M.Steyn, 2015

Steyn, Hester M. & Van Wyk, Abraham E., 2015, Taxonomic notes on the Acanthopsis disperma-hoffmannseggiana complex (Acanthaceae, tribe Acantheae), with an interim key to members of the genus, Phytotaxa 219 (1), pp. 1-26 : 8-10

1. Acanthopsis tuba H.M.Steyn , sp. nov. ( Figs. 1 , 3A , 4 )

Acanthopsis tuba differs from all other species of Acanthopsis in having a markedly elongated (> 15 mm long) corolla tube.

Type: —[ SOUTH AFRICA. Northern Cape:] Little Namaqualand, Steinkopf District. Flats at Anenous , 530 m, (2917 BA), 20 August 1925, Marloth 12222 (holotype PRE0129530 -0!; isotypes PRE0863286-0!, NBG0274649 -0!) .

A. carduifolia sensu Williamson (2000: 188 fig.), misapplied name, non (L.f.) Schinz.

Perennial, compact subshrub, 80–100 mm tall with reduced branching. Leaves oblanceolate, 40–60(–70) × 8–10(–12) mm; margin undulate, coarsely dentate spinose, spines strong, (2–)4–8(–14) mm long, yellow; almost glabrous or with minute appressed to spreading hairs; base attenuate, decurrent. Inflorescences 2–5 per plant, 45–70 mm long, 12–16(–20) mm in diameter. Bracts hemispherical, obovate or wedge-shaped, 22–32(–35) mm long, base 15–16 mm long, lower bracts truncate, ending in 7 primary spines (central primary spine simple, rest with short basal secondary spines); middle and upper bracts ending in 7 primary spines; central primary spine often compound (with 2 pairs of marginal secondary spines); other primary spines usually with 1 or 2 basal and (0)1 or 2 marginal secondary spines; spines spreading in fruit; bract base glabrous to hirsute with deflexed to spreading short hairs and scattered long hairs; ring of long, silky hairs adaxially at base of spines; spines almost glabrous or villose (long, silky hairs interspersed with short hairs and sparsely scattered to occasional short, glandular hairs). Bracteoles sickle-shaped, 8–9 mm long, silky hairy especially at tip, rarely also with glandular hairs. Calyx with dorsal sepal obovate, apiculate, 11–14 mm long, silky hairy especially abaxially, rarely also with glandular hairs, 7–9-veined from base; ventral sepal ovate, 10–13 mm long, silky hairy especially abaxially, occasionally also with glandular hairs, 5–7-veined from base; lateral sepals 9 mm long, densely silky hairy especially at base, occasionally also with glandular hairs. Flowers blue to deep blue-purple with white throat and dark purple ring around entrance to throat; corolla 45–50 × 10–12 mm, tube (15–) 25–35 mm long, villose; corolla limb recurved, central lobe longer than wide or equal, slightly constricted at base, truncate to emarginate. Stamens with purple-black anthers, 2 mm long; filaments 4–5 mm long, glandular, hairy towards base. Style with patch or ring of glandular hairs at base. Capsules and seeds not seen.

Etymology: —The specific epithet refers to the markedly elongated corolla tube; from the Latin tuba , a Roman bronze war trumpet with a long straight tube.

Distribution, ecology and phenology: —Centred in the core part of the Gariep Centre of Endemism ( Van Wyk & Smith 2001) and only known from three localities between Anenous and Helskloof in the Richtersveld, Northern Cape, South Africa ( Fig. 1 ). This distribution falls within the Succulent Karoo Biome ( Rutherford & Westfall 1994, Low & Rebelo 1996, Mucina & Rutherford 2006) and within the Southern Richtersveld Scorpionstailveld (SKr 13) and Central Richtersveld Mountain Shrubland (SKr 1) vegetation types ( Mucina & Rutherford 2006). The mean annual precipitation in its range is 80–200 mm, received mainly in winter. This species seems to be habitat specific (L. von Staden, pers. comm. 2014) and specimens were collected at elevations of 350–600 m on plains or hill slopes in well-drained rocky soils. Flowering time: August and September.

Notes: —The specimen collected from the top of Helskloof (Oliver, Tölken & Venter 181) has villose bract lobes and the leaves are covered with minute appressed to spreading hairs in contrast to the almost glabrous specimens from further south.

More fieldwork is needed to determine the full distribution range and abundance of this species.

Conservation status: — Acanthopsis tuba has an Extent of Occurrence of 1619 km 2, and is known from only three locations, all in areas where severe overgrazing and trampling by domestic livestock are causing continuing loss and degradation of the habitat. Searches have failed to locate this species at two of the three known historical locations, and continuing population decline is inferred. It is therefore categorised as Endangered according to Red List criterion B1ab(iii,v) ( IUCN 2001) (L. von Staden, pers. comm. 2014).

Additional specimens examined: — SOUTH AFRICA. Northern Cape: Richtersveld. Vandersterrberg ; NE of Khubus. N end of the top of Helskloof and SE of Paradysberg western slopes to summit, (2817 AC), 28 August 1977, Oliver, Tölken & Venter 181 ( PRE!) ; Richtersveld. Karuchabpoort, 9 km south of Lekkersing. Main hills north of poort, 350 m, (2917 AA), 8 September 1977, Oliver, Tölken & Venter 800 ( PRE!) ; Richtersveld, Karachab Poort, between Eksteenfontein and Lekkersing, plateau of steep rocky slopes on northern side of road, near Eksteenfontein end of poort, (2917 AA), 28 August 2014, Von Staden CNR 9139 ( PRE!) .

Figures

FIGURE 1. Known distribution of species within the Acanthopsis disperma-hoffmannseggiana complex. A: A. ludoviciana (●) and A. tuba (Δ), B: A. adamanticola (▲), A. disperma (○), A. dispermoides (□), A. hoffmannseggiana (■) and A. villosa (ۗ).

FIGURE 3. Comparison of floral parts in members of the Acanthopsis disperma-hoffmannseggianna species complex (from left to right): bract(s) (abaxial views), bracteoles, calyx (4 sepals) and flower. A. A. tuba. B. A. ludoviciana. C. A. adamanticola. D. A. villosa. E. A. hoffmannseggiana. F. A. disperma. G. A. dispermoides. Note: if two bracts per species are illustrated, the one on the left is from lower down in the same inflorescence. Scale bar = 10 mm. Vouchers:A = Von Staden CNR 9139 (PRE), B = Koekemoer 4370 (PRE), C = Germishuizen 10074 (PRE), D = Koekemoer 4398 (PRE), E = Steyn 1907 (PRE), F = Koekemoer 4187 (PRE), G = Steyn 1912 (PRE).

FIGURE 4. Acanthopsis tuba: morphology. A & B. Habit. C. Flower. D & E. Leaf indumentum. F–H. Bract. I. Calyx. J. Flower (corolla lobes blue-purple; throat white). K. Glandular hairs at base of style. Vouchers: D, I, K = Oliver, Tölken & Venter 181 (PRE), E = Oliver, Tölken & Venter 800 (PRE), F–H, J = Marloth 12222 (PRE). Photographs: L. von Staden (A & B), P. van Wyk (C).