Genoplesium rhyoliticum D.L.Jones APNI*
Synonyms: Corunastylis rhyolitica (D.L.Jones) D.L.Jones & M.A.Clem. APNI*
Description: Terrestrial herb 10–18 cm high.
Leaf 10–15 cm long by 2.0–2.5 mm wide, terete. Inflorescence dense, 2–4 cm long, 5–20-flowered.
Flowers c. 4 mm across, semi-erect, dark purplish black. Dorsal sepal narrow-ovate, c. 4.5 mm long, c. 2 mm wide, glabrous, greenish with three longitudinal purple-black stripes medially and purple-black, entire, margins. Lateral sepals linear to lanceolate, c. 5 mm long, c. 1 mm wide, not gibbous at the base, parallel or slightly divergent. Petals narrow-ovate, c. 4 mm long, c. 1 mm wide, greenish with purple-black stripes, margins entire, apex acuminate. Labellum obovate, c. 3.5 mm long, c. 1.7 mm wide, dark purple-black, margins with numerous, coarse, spreading cilia to 0.5 mm long; callus narrow-triangular, extending to the labellum apex. Column around 2 mm long, erect; foot c. 0.5 mm long, projecting forward and curved upward. Column wings shallowly divided by a narrow sinus into two lobes, the lobes not divergent; lower lobe acute, bearing cilia around its apex, which shorten along the dilated lower margin, surface papillose; upper lobe obtuse to rounded, ligulate, surface smooth and margins entire.
Distribution and occurrence: Grows under shrubs; known from a single rhyolite outcrop near Pambula.
NSW subdivisions: SC
Threatened species: NSW BCA: Endangered; Commonwealth EPBC: Endangered
Genoplesium rhyoliticum can be recognised by the combination of 1) ciliate trichomes on the labellum margins; 2) the absence of cilia on other floral segements, whose margins are entire; 3) the column wing shallowly divided into two lobes, the lower of which is acute and bears cilia about its apex, and has shorter ciliolate margins on the dilated medial margin; 4) the acuminate petals, whose apex does not bear a gland; 5) the labellum callus extending into the acuminus at the labellum apex; 6) the flowers being c. 4 mm wide. Genoplesium rhyoliticum is similar to G. oliganthum but can be distinguished by its smaller flowers (4 mm v. 8-9 mm wide); the labellum whose callus runs into the terminal acuminus (v. callus ending below the acuminus; and the elliptic dorsal sepal (v. ovate-triangular in G. oliganthum. When described (Jones 1991), Genoplesium rhyoliticum was diagnosed against G. morrisii, from which it is readily distinguished by the absence of trichomes on the dorsal sepal and petal margins. This same feature distinguishes G. rhyoliticum from G. ostrinum.
Text by D. L. Jones, updated by Matt A.M. Renner (17 June 2020).
Taxon concept: Flora of NSW 4 (1993) and Jones (1991) New taxa of Australian Orchidaceae. Australian Orchid Research 2: 1-208.
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