Disa staerkeriana McMurtry & Bytebier, 2015

Bytebier, Benny, 2015, Disa staerkeriana (Orchidaceae): a new species from Mpumalanga, South Africa, Phytotaxa 203 (2), pp. 192-198 : 192-194

Disa staerkeriana McMurtry & Bytebier , sp. nov. ( Figs. 1–4 )

Type:— SOUTH AFRICA. Mpumalanga: Lydenburg, west of Sabie, Hartebeesvlakte , 2200 m, 25°05’S, 30°39’E (2530 BA), 25 January 2014, McMurtry 15222 (holotype: NU!; isotypes: BOL!, BNRH!, HSMC!, WAG!) .

Diagnosis—similar to Disa amoena from which it can be distinguished by the shorter spur and the smaller flowers; and to Disa montana from which it can be distinguished by smaller and differently shaped petals, and by the much shorter inflorescence with fewer flowers (Table 1).

Erect terrestrial herb 250–350 mm tall. Leaves 6–8, slightly spreading at 5–15° from axis, rigid, conduplicate, linear-lanceolate, (56–) 80–90 (–105) mm long × 1.5–2.8 mm wide, 3–5 mm wide when flattened, with three main veins, veins and margins translucent, light straw-coloured. Inflorescence compact, subsecund, 55–75 mm long × 30–35 mm wide, 5–13-flowered. Bracts 16–28 mm long × 4.5–5 mm wide, acute to acuminate, pale maroon-pink, scarious at anthesis. Ovary green, tinged reddish, obliquely patent, ± 15mm long. Flowers white often suffused pale pink, lightly and randomly speckled violet, sweet-soapy scented; 10 mm wide, 5–8 mm tall. Median sepal white flushed pale pink along main vein, finely speckled violet, oblong, shallowly canaliculate, rounded, 10–13 (–15) mm long × 9–11 mm wide, lateral lobes recurved. Spur white, suffused pink dorsally, 8–10 mm long × 1 mm wide medially, patent, gently decurved to ± straight, narrowly funnel shaped, nectariferous. Lateral sepals white, flushed pale pink, randomly speckled violet, porrect, ± parallel, oblong, 11–14 mm long × 6–8 mm wide, subacute, apiculate, apiculus (0.5–) 1–2 mm long. Petals white, translucent, variously marked violet apically (rarely pure white), erect next to the rostellum, narrowly oblong, subfalcate, variably trilobed distally, 4–6 mm long × ± 2 mm wide, anticous basal lobe ± 1 mm in diameter. Lip white, randomly speckled violet, rarely unspotted, lorate to very narrowly spathulate, 10–11 mm long × 2–3 mm wide, apex acute to obtuse, slightly decurved, margins ± revolute. Anther purple-brown, horizontal ± 1.5 mm long. Stigma white, equally tripulvinate, 1.5 mm in diameter. Rostellum lateral lobes square, central lobe vestigial.

Affinities and diagnostic characters: — Disa staerkeriana is a member of section Stenocarpa Lindley (1838: 347 , 352) sensu Bytebier et al. (2008) on the basis of its rigid, cauline leaves, erect petals free from the rostellum and square lateral rostellum lobes.

D. staerkeriana is most likely closely related to the sympatric D. amoena Linder (1981: 236) but is distinguishable by its spur length, flower size and flower shape. The spur in D. amoena ranges between 25–45 mm and is amongst the longest in the section Stenocarpa , whereas that of D. staerkeriana is only 8–10 mm long ( Figure 3B ). The flowers of D. staerkeriana are also smaller compared to those of D. amoena ; dorsal sepal ranges from 10–15 vs. 15–25 mm, lateral sepals 11–14 vs. 13–20 mm, petals 4–6 vs. 7 mm and lip length 11–12 vs. 15–20 mm. With regard to shape, the flowers of D. staerkeriana are rather cupped in comparison to the much more open D. amoena flowers ( Figure 3 ). Lastly, flower colour is uniform within the population of D. staerkeriana , whereas it is variable within and between populations of D. amoena .

Disa staerkeriana is also somewhat similar to D. montana Sonder (1846: 90) but differs in several aspects (Table 1). In particular the petals are very different ( Figure 4 ). They are smaller (4–6 mm vs. 6–9 mm), have a different shape (narrowly oblong and vs. narrowly oblanceolate) and a differently shaped apex (trilobed vs. acute). Disa staerkeriana is in general also a much smaller plant. The inflorescence is considerably shorter (55–75 vs. 150–220 mm) and the number of flowers per inflorescence is considerably less (5–13 vs. 15–22). D. montana has only been recorded from the southern Drakensberg (Eastern Cape and KwaZulu-Natal Provinces), which is about 600 km to the southwest in a straight line, from the only currently known locality of D. staerkeriana . Furthermore, D. montana flowers from late November until the middle of December, whereas D. staerkeriana flowers in late January.

Flowering Time: —late January.

Etymology: —Named for Herbert and Helga Staerker of Vienna, Austria who have spent the last nine years photographing South African orchids and discovered this species in January 2013.

Distribution and altitudinal range: —Currently known from a single population in which 30 individuals were counted, covering an area of ± 500 × 700 m in size between 2160–2231 m elevation.

Habitat and associated species: —The habitat falls within the Wolkberg Centre of Plant Endemism ( Matthews et al. 1993) on the upper reaches of the Hartebeesvlakte, an area of pristine grassland. The individuals are scattered, rarely closely adjacent, on a steep south-easterly slope, growing between widely scattered Black Reef quartzite boulders in well-drained Lydenburg Montane Grassland (Gm18) ( Mucina & Rutherford 2006). At anthesis of D. staerkeriana only three other orchid species were found in the immediate surrounds, namely Disa clavicornis Linder (1984: 261) , Neobolusia tysonii ( Bolus 1884: 485) Schlechter (1895: 5) and Satyrium longicauda Lindley (1838: 337) . Other associated flora of Disa staerkeriana includes Alepidea cf. setifera Brown (1896: 161) , Berkheya echinacea (Harvey in Harvey & Sonder, 1865: 495) O.Hoffm. ex Burtt Davy in Burtt Davy & Pott-Leendertz (1912: 121), B. radula (Harvey in Harvey & Sonder, 1865: 491) De Wildeman (1901: 89), Chaenostoma neglectum J.M.Wood & M.S.Evans in Wood (1897: 352), Cyphia cf. stenopetala Diels (1898: 112) , Erica atherstonei Diels ex Guthrie & Bolus in Thiselton-Dyer (1905: 120), Inezia integrifolia (Klatt in Schinz, 1896: 840) Phillips (1932: 297), Mohria marginalis (Savigny in de Lamarck & Poiret 1798: 655) Roux (1990: 401) , Monsonia cf. burkeana Planch. ex Harvey in Harvey & Sonder (1860: 255), Streptocarpus dunnii Hooker (1886 : t. 6903) and Xyris cf. obscura N.E.Br. in Thiselton-Dyer (1902: 16).

Specimens examined:— SOUTH AFRICA. Mpumalanga: Lydenburg, west of Sabie, Hartebeesvlakte (2530BA), 25 January 2013, Staerker s.n. (NU!), Staerker sub McMurtry 14795. (HSMC!).

Conservation: —The number of narrow endemic Disa species in the Mauchsberg-Hartebeesvlakte area has been further increased by the addition of D. staerkeriana . The area is an important refuge for a surprising number of range restricted orchid species. Schizochilus lilacinus Schelpe ex Linder (1980: 426) , Disa alticola Linder (1981: 252) , D. clavicornis , D. klugei , D. vigilans and now D. staerkeriana are all endemic to this area. The Hartebeesvlakte covers an area of 1970 hectares and is an important mountain catchment area, presently protected by the Department of Agriculture, Forestry and Fisheries (M. Lotter, pers. com.).

Figures

FIGURE 1. Disa staerkeriana. A. Plant in grassland habitat. B. Close up of inflorescence.

FIGURE 2. Dissected flower of Disa staerkeriana (left) and the unspeckled deep pink form of D. amoena (right).

FIGURE 3. Close-up comparison of single flowers of the speckled light pink form of Disa amoena (left) and D. staerkeriana (right). A. Front view. B. Side view.

FIGURE 4. Close-up comparison of the petal of Disa montana (left), Disa staerkeriana (middle) and Disa amoena (right).