Plants 140–240 mm high. Corm globose, 10–15 mm diam.; tunics of coarse, matted fibres, accumulating with age and forming short neck around base of stem. Stem erect, unbranched, ± 1.5 mm diam. below spike. Cataphylls dry and papery, reddish brown. Leaves 4, lowermost inserted below ground, blade exceeding spike, ± dry at flowering, linear, 200–250 × 2–3 mm, closely 3- or 4-ribbed, upper 3 leaves cauline, sheaths ± imbricate and enveloping entire stem, blades successively shorter, up to 100 mm long, uppermost leaf sheath ± reaching to base of spike, with short blade 20–30 mm long. Spike erect, densely 7–15-flowered; bracts imbricate for 1/2 to 2/3 length, 8–10(–13) mm long and two or three internodes long, outer acute, either green below or entirely brown and leathery, conspicuously and closely veined, with narrow membranous margins, inner bract slightly shorter, bifid, ± membranous with narrow brown zones along veins. Flowers suberect, cream-coloured to pale flesh-pink, flushed purple on tube, lower three tepals with median linear maroon streak extending halfway along blade; perianth weakly zygomorphic; tube slightly curved outwards in distal 3 mm, (17–)20–23 mm long, ± 1.5 mm diam. at mouth, ± cylindrical but widening slightly distally, exserted 13–15 mm beyond bracts; tepals linear-oblanceolate, inner three slightly smaller, spreading and slightly cupped, 12–15 × 1.5–3.0 mm. Stamens arcuate; filaments 4–5 mm long, exserted 2–3 mm from tube; anthers 4 mm long, blackish purple; pollen purple. Ovary obovoid, 2.0–2.5 mm long; style arching above anthers, dividing between base and middle of anthers, branches, ± 3 mm long, divided to near base. Capsules narrowly ovoid, 5–7 × 3 mm. Seeds ellipsoidangled, ± 2 mm long, yellowish brown, testa striate-colliculate.
Thereianthus elandsmontanus is distinguished from the other ribbed-leaved species in the genus (ser. Thereianthus), by its creamcoloured to pale flesh-pink flowers with moderately long tube, 17–23 mm long and 1.5–1.8 × as long as the narrow, ± linear tepals which are 1.5–3.0 mm wide, the lower three each with a conspicuous maroon median streak extending over the lower half. Unfortunately the flowers do not retain their colour in the herbarium, drying bluish lilac. T. elandsmontanus is most likely to be confused with T. spicatus, which has a tube of similar length and which also occurs at Elandsberg Nature Reserve but this species has blue (rarely white or pink flowers) with broader, lanceolate tepals, 3–5 mm wide, the lower three marked with a white flash at the base bordered distally by a small blue chevron, and slightly shorter filaments, 3–4 mm long vs 4–5 mm long. Although these differences may seem minor, we are familiar with both species on the reserve and are convinced that they are distinct. Another related species, T. longicollis from the nearby Saronsberg and Elandskloof Mtns, has a much longer tube, 25–40 mm long and 2.0–2.5 × longer than the tepals, the lower three of which are marked with a dark, transverse chevron. The leaves in T. elandsmontanus are often slightly broader than in T. longicollis, 2–3 mm vs 1–2 mm, with 3 or 4 vs consistently 3 raised veins. We considered the possibility that the Elandsberg plants might be an isolated, short-tubed form of this species, possibly recognizable at subspecific rank but the consistent morphological and ecological differences between them suggest that recognition at species level is more appropriate. Typical T. longicollis is a montane species and the clear separation in tube length between it and T. elandsmontanus argues for complete genetic isolation between them.
Thereianthus elandsmontanus is known from a single small population on Slangkop, a low sandstone ridge on Elandsberg Nature Reserve near the foot of the Elandskloof Mtns near Hermon.
Just a couple of dozen individuals were found. Although only discovered two years after a fire had cleared the site, it is clear that the species also flowered in the first year after the burn since one of the individuals had the remains of a previous flowering stem still associated with the corm.
The moderately long-tubed, cream-coloured to fleshpink flowers with conspicuous narrow, maroon markings on the lower three tepals bear a striking resemblance to those of several co-occurring species of Iridaceae, notably Lapeirousia anceps (L.f.) Ker Gawl. and Tritonia undulata (Burm.f.) Baker, that are adapted to pollination by long-proboscid tabanid flies in the genus Philoliche, and it is likely that Thereianthus elandsmontanus is also a member of this pollination guild.
Flowering time: Nov.
History: the most recently discovered species in the genus, Thereianthus elandsmontanus was collected for the first time in November 2010 on a low sandstone ridge on Elandsberg Nature Reserve. This ridge has been explored botanically since 1996 by the owners of the property, Dale and Elizabeth Parker, but the species was only noticed when it flowered in response to a controlled burn of the ridge in early 2008.
Etymology: the name derives from the Elandsberg Nature Reserve, where the species appears to be endemic.