Genoplesium ostrinum D.L.Jones APNI*
Synonyms: Corunastylis ostrina (D.L.Jones) D.L.Jones & M.A.Clem. APNI*
Description: Terrestrial tuberous herb.
Leaf terete, 15–28 cm long, c. 0.15 cm wide, dark green, base reddish, lamina subulate, closely sheathing the scape which is 10–22 mm long by 1.5–2 mm wide, ending 3–5 cm below the first flower.
Inflorescence 20–35 cm tall, bearing 3–10 flowers in a moderately dense spike 10–30 mm long. Floral bracts closely sheathing, transversely ovate-elliptic c. 1.5 mm long and 2 mm wide, apiculate. Ovary linear-obovoid, c. 5 mm long, asymmetrically arcuate. Flowers porrect c 8.5 mm wide, dark purple with darker stripes on the dorsal sepal and petals and a dark purple labellum. Dorsal sepal broadly ovate-lanceolate, 5.5–6 mm long by around 3 mm wide, concave, with 3 prominent medial purple stripes and purple-red margins which bear numerous purple-red multicellular filiform trichomes of varying length in the upper three-quarters of the margin, apex acuminate. Lateral sepals obliquely erect, widely divergent, linear lanceolate, slightly sinuous, c. 6.5–7.5 mm long by 1.5 mm wide, gibbous at the base, distal margins inrolled, apex (sub)acute, with no gland. Petals widely spreading, asymmetrically ovate-lanceolate, margins rounded in basal half then more or less abruptly narrowed in the upper half and tapered to an acuminate apex, c. 3.5–4 mm long by 1.5 mm wide, with 3 prominent purple stripes, margins purple with multicellular filiform trichomes to 0.3 mm long on the margins, apex without a gland. Labellum porrect, hinged on a short, circinate column foot, mobile in a breeze, linear-obovate, c. 5 mm long by 1.6 mm wide, thin and fleshy, deflexed at both base and in the vicinity of the apex, margins with numerous purple multicellular filiform trichomes of variable length, longest c. 1 mm, tending shorter toward the base, longest in the upper third of the labellum margin; apex with an acuminate apiculus; callus occupying less than half the area of the ventral surface of the lamina, extending two–thirds of the distance to the labellum apex, dark purplish-black, colluviate, thickest and broadest just above the base then constricted before expanding to an obtuse or emarginated apex. Column c. 3 mm long and 1.5 mm wide, pale purple to white with a purple wash. Column foot ligulate, c. 1 mm long, circinate. Column wings notched in the distal half, lobes unequal, slightly divergent, upper lobe shorter, linear, whitish, obtuse, margins entire; lower lobe longer, linear-lanceolate, slightly falcate, with dark purple wash, apex acuminate, the lower margin with with short papillae. Anther c. 1.3 mm long with a filiform rostrum to c. 1.0 mm long. Pollinarium c. 1.2 mm long, pollinia c. 1.0 mm long yellow, coarsely granular. Stigma ovate-elliptic c. 1 mm long by 0.6 mm wide.
Flowering: Recorded flowering from February to April.
Distribution and occurrence: Among low shrubs and tussock in heath and open Eucalyptus rossii woodland.
NSW subdivisions: ST
Genoplesium ostrinum can be recognised by 1) the ciliate dorsal sepal and petals; 2) the dark-purple flowers with striped dorsal sepal and petals; 3) the absence of glands on petals on sepals; 4) the apiculate labellum apex; 5) the densly ciliate labellum margins; 6) the labullum callus extending around two thirds of the labellum width, consticted at its middle, and appearing cleft at its apex; 7) the column wings divided by a narrow sinus into two unequal, narrow lobes with acuminate apices, the lower of which bears a few cilia. Genoplesium ostinum is similar to G. morrisii, and differences between these two are difficult to quantify. Jones (2001) confines G. morrisii to Victoria and Tasmania, and states that it has 'larger flowers, with much thicker segments and a broader, ovate oblong labellum with strongly developed colluviate callus' than G. ostrinum. The Flora of Victoria gives the width of G. morrisii flowers as 'c. 9 mm', which is comparable to the width of flowers on plants from NSW. Dimensions for flower segments, including labellum width, are also comparible among Victorian and NSW plants. Further investigation of the relationships between G. morrisii and G. ostrinum is required.
Text by Description based on D.L.Jones (2001), with modification by M.A.M.Renner (10 May 2020).
Taxon concept: Jones DL (2001) Six new species and a new combination in Genoplesium R.Br. (Orchidaceae) from eastern Australia. The Orchadian 13(7): 293-307.
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