Corybas rivularis

Detailed description

Colonial, terrestrial, tuberous, glabrous, late winter to summer-green herb. Tuberoids globose to ellipsoid on extended roots. Plant at flowering to 40 mm tall. Leaf solitary (rarely paired), fleshy, subsessile or with a short petiole 5–10 mm long; lamina 20–30 × 15–25 mm long, oval to orbicular, apiculate, rounded to cordate at base; dark green to yellow green, margins and sometimes whole of upper surface flecked with purple or red, underside silvery pellucid. Flower erect, mostly large for plant, (15)–20–(25) mm long, held well above leaf, mostly dark crimson black; peduncle short and stout, 2.5–3.5 mm long. Ovary 8.5–10.0 mm long, narrowly oblong to ellipsoid, yellow-green, erect or slightly curving forward over leaf; subtended by two unequal floral bracts, the smaller projecting toward leaf, 1.5–2.0 mm long, linear-subulate to lanceolate-subulate, terete, pale green to cream, spotted or flecked with crimson, the larger smaller than, equal to or exceeding the ovary, (2.5)–8.8–(11.0) mm long, lanceolate to linear-lanceolate, curved, deeply keeled and mostly closely sheathing ovary for about one third to half of length, apex acute, green, usually with purple or reddish striae or flecks. Dorsal sepal membranous, more or less equal to labellum length 15–20 mm long, greenish with purple-red crimson-black striate or flecks, lanceolate-acuminate, apex acute, erect then arched forwards, or downwards, very rarely upwards. Lateral sepals and petals subsimilar, 20–30 mm long, filiform, cream to yellow green more or less flecked with red, greatly exceeding the labellum, held well above leaf. Labellum conspicuous, dark crimson-black, auriculate at base,; labellum tube 1.5–3 mm long, erect at first then abruptly deflexed at c. 90 degrees and expanding into a gradually broadening lamina; lamina (15)–20–(25) × (6)–10–(16) mm, narrowly obtuse when flattened, upper margins sharply folded inwards, upper ⅓–½ more or less overlapping, lower surface spreading and deeply grooved; apex usually held well above leaf; margins initially entire, becoming erose to finely and irregularly denticulate on either side, and with a short to moderately long down-curved apiculus; apiculus not or only rarely touching leaf.