Common name: Trifid midge orchid
Genoplesium trifidum (Rupp) M.A.M.Renner APNI*
Synonyms: Genoplesium trifidum (Rupp) D.L.Jones & M.A.Clem. APNI*
Corunastylis trifida (Rupp) D.L.Jones & M.A.Clem. APNI*
Prasophyllum trifidum Rupp APNI*
Description: Tuberous terrestrial herb.
Leaf terete, 110–330 mm long, 1–2 mm wide, lamina sheathing the scape, linear, free lamina lamina 15–30 mm long and 2–3 mm wide, ending below or level with the first flower.
Inflorescence 160–380 mm long, bearing 10–42 flowers on a spike 12–43 mm long; flowers opening in sequence from the base; pedicel and ovary straight, 1–4 mm long, lengthening with age such that young spikes with newly opened flowers are densely crowded while older spikes with all flowers open and presenting may be openly spaced. Flowers porrect to deflexed, dorsal sepal 3 mm long, 1.5 mm wide, triangular-ovate, concave and inflated at medial base, apex shortly attenuate, not bearing a gland; lateral sepals 4 mm long, 1 mm wide, linear-lanceolate, widest just above base, concave toward apex sometimes margins overlapping and so tubular, acute, bearing a small dark orange to fuscous unstalked ovoid gland around 0.1 mm diameter; petals 2.5 mm long, 1 mm wide, triangular-falcate, outer surface papillate in distal third, dorsal margin straight in lower half above weakly ampliate base, then curved through 45° to the apex, margin crenulate to shortly ciliolate in distal half, ventral margin straight at middle then arched through 15–30°, margin shortly ciliolate in outer half, apex acute, sharply inwardly curved and with a pale opaque circinate-falcate gland attached and presented on the inner side of the petal, gland 0.5–0.6 mm long; labellum 2.5 mm long, 1.2 mm wide, elliptic, widest at midpoint, apex acute, margins ciliolate in distal half, entire in proximal half, with callus linear in distal two thirds of the labellum and extending almost to the labellum apex, flaring toward labellum base in the basal third where it becomes ridged marginally, ridges extending to and incorporated into the labellum margin, callus surface papillate medially, papillae formed by prorate surface cells, and ciliolate marginally; attachment narrow, articulated, at apex of column foot. Column 1.5–2.0 mm long not including column foot, 1 mm wide; column foot present, 0.5 mm long, curved; wings subequally bilobed, around 1 mm long and 0.625 mm wide, divided to 0.4 their length, dorsal lobe slightly ligulate, apex obtuse or rounded, margins entire, slightly broader than ventral lobe; ventral lobe narrow triangular, apex acuminate, margin and surfaces shortly and closely ciliolate; anther versatile, 0.75 mm long, ovate, with a filiform rostrum whose apex is emarginate or weakly and shortly bifurcate; stigma ampulliform but with truncate apex and base, the base faintly emarginate, surface concave along lateral and basal margins. Pollinarium not seen sufficiently intact for description.
Flowering: Recorded flowering from January to May, with most flowering specimens collected in April and May.
Distribution and occurrence: Genoplesium trifidum is endemic to New South Wales and is currently known with certainty only from the north shore of Sydney, in the vicinity of Castlecrag, Castlecove and Roselle, and from Oxford Falls. All reports from the North Coast of New South Wales and Queensland are referable to other species. All herbarium specimens are flowering, with most being collected in April or May, suggesting this is primarily an autumn-flowering species, though flowering at other times of the year is possible, as demonstrated by a collection made in January at Oxford Falls. No information on habitat or microsite is recorded in association with the specimens. The most recent genuine and correctly identified specimen held by the National Herbarium of New South Wales was collected in 1949.
NSW subdivisions: NC, CC
Genoplesium trifidum can be recognized by the combination of 1) closely ciliolate labellum margins, wherein the marginal cells are elongate, and their ends are free from neighbouring cells; 2) the papillose callus surface; 3) the elliptic-obovate labellum whose apex is acute; 4) the pale, circinate to hook-shaped gland attached to the apex of each petal and typically presenting on the inner surface of the petal; 5) the absence of glands on the apex of the dorsal and lateral sepals, or presence of a minute usually fuscous gland-like protruberance; 6) the broad upper column arm that narrows to an obtuse to rounded apex, the lower column arm being narrow acuminate, and papillose to ciliolate at the apex. The pale circinate to hook-shaped gland attached to the apex of each petal will immediately distinguish G. trifidum from all other similar species including G. rufum.
APNI* Provides a link to the Australian Plant Name Index (hosted by the Australian National Botanic Gardens) for comprehensive bibliographic data
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