NEW SOUTH WALES FLORA ONLINE

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Synonyms: Oligochaetochilus petrosus (D.L.Jones & M.A.Clem.) D.L.Jones & M.A.Clem. APNI*

Description: Terrestrial herb

Leaves narrowly elliptical to narrowly obovate, 15–25 mm long by 6–9 mm wide, sessile to subsessile, obtuse to subacute, 6–10 in a sparse radical rosette, usually senescent at flowering.

Scape 9–15 cm tall, slender to moderately stout, with 2–4 closely sheating, ovate-lanceolate, acute to acuminate stem leaves. Floral bracts 10–23 mm long, ovate-lanceolate, closely sheating, acute to acuminate. Pedicels 14–20 mm long, slender. Ovary 8–10 mm long. Flowers 1–8, transparent with broad brown lines and red-brown patches in the galea and sepals, porrect; galea gibbous at the base, shallowly curved, decurved suddenly to the apex; proximal petal flanges widely separated and not closing off the base of the galea. Dorsal sepal 18–20 mm long, cucullate, obliquely erect, abruptly decurved in distal third, reddish brown with darker lines and transparent areas, apical point 8–10 mm long, filiform, long acuminate, porrect to upcurved. Lateral sepals deflexed, red-brown with darker lines and transparent areas; conjoined part deeply concave, 6–8 mm long by 14–16 mm wide, the margins thickened and slightly incurved with numerous white trichomes c. 1 mm long; sinus narrow, the lobes divergent; free points 14–20 mm long, filamentous, more or less parallel. Petals ovate-lanceolate, 16–19 mm long by 5–6 mm wide, long acuminate, curved at the base, transparent with red-brown lines, dorsal ridge with numerous trichomes, proximal flange poorly developed. Labellum highly irritable on a curved claw c. 3.5 mm long; lamina oblong-elliptic, 7–9 mm long by 3.0–3.5 mm wide, brown, thin-textured, constricted in the proximal third, widest above the middle, margins irregularly scalloped, apex broadly obtuse; lateral margins with 9–12 pairs of stiff, white, spreading trichomes c. 1.2 mm long; basal lobe slightly raised, sloped backward, a pair of prominent erect trichomes c. 3 mm long arising near the constriction; underside with a narrow, deep, central channel extending nearly to the apex, bordered by a band of pale, siliceous cells.

Habitat Photo Lachlan Copeland

Habit Photo Lachlan Copeland

Flower Photo Lachlan Copeland

Flowering: September– November

Distribution and occurrence: Southern New South Wales, within the Riverina District.

Grows in sparse sclerophyll forest, in crevices and on ledges on rock outcrops; confined to the Riverina district.
NSW subdivisions: SWS

AVH map***

Pterostylis petrosa is similar to P. biseta but can be distinguished by its rosettes having 6–10 leaves that are 1.5–2.5 cm long and 6–9 mm wide; the scape is 9–15 cm high and 1–8-flowered; the lateral sepal free points are 14–20 mm long; and the labellum is oblong-elliptic to elliptic and has 9–12 pairs of marginal trichomes; the galea is wider than P. biseta, the free points on the sepals are shorter, and the petals are longer.