Acianthus saxatilis
Plant: Glabrous, terrestrial, tuberous herb growing in small colonies.
Stem: Stem erect to slightly bent forward, widest and darkest green at base, 40-90 mm tall, 1.5-3 mm thick.
Leaf: Porrect, cordate, 38-70 x 20-90 mm, light green above, reddish green to light greenish purple beneath, entire; veins not prominent; apex attenuate to acuminate.
Inflorescence: Raceme erect, 3-8 cm tall, slender, thinner than the stem, 1-5[-8]-flowered.
Floral Bracts: Prominent, cordate, 4-12 x 4-13 mm, light green, foliose.
Ovary: Linear, 8-10 x 1-2 mm, curved, light green.
Flowers: Largest for the genus, porrect, 10-13 x 5-7 mm, light green with faint light brown margins on sepals; labellum light greenish-brown to greenish-yellow with light brown margins, brown callus and darker brown apex.
Dorsal Sepal: Ovate-lanceolate, 8-12 x 4.5-8 mm, cucullate, acute to apiculate.
Lateral Sepals: Connate at the very base then free, projected obliquely forwards below the labellum and forming a flat to slightly concave platform- like structure; each sepal asymmetrically oblanceolate, 9.5-14 x 3-3.5 mm, narrowed to the base.
Petals: Porrect to upswept, partially hidden by the dorsal sepal, obliquely lanceolate, falcate, 7-9 x c. 3 mm, acuminate.
Labellum: Sessile, obliquely porrect, 8.5-10 x 4.5-5 mm, elliptical to elliptical lanceolate, cymbiforme, thickest in basal half, flat to shallowly concave; margins entire or distally irregular; apex acute to subacute or apiculate. Callus consisting of paired basal glands and a narrow brownish central band; glands mostly hidden, tonsil-like, each 1.5-2 mm long; central band c. 1 mm wide, restricted to proximal two-thirds of labellum.
Column: Erect, 4.5-6.5 mm long, shallowly curved, green. Anther 0.6-0.8 mm long, rounded, with light brown band, without a rostrum. Stigma elliptical, c. 0.7-0.8 mm wide. Pollinarium c. 0.8 mm wide, consisting of two hemipollinaria, each comprised of a small hemivisidium and four poillinia in two unequal pairs; viscidium c. 0.2 mm wide; pollinia clavoid, light yellow, the smaller four c. 0.35 mm long, the larger four c. 0.5 mm long.
Capsules: Ellipsoid, 10-12 x c. 3 mm.
Type: Queensland; Lightning Falls, Lamington National Park, 12 Feb. 2010, M.T. Mathieson MTM0606, L.Rintoul and M.Pears (holo BRI! AQ792112)
Distribution: To date this species is known only from two localities in the Border Ranges region of south- eastern Queensland and north-eastern New South Wales. It is extremely localised and forms relatively small colonies. At the Lightning Falls locality it grows at about 1,100m alt., under ferns and shrubs among wet basaltic rocks in dense subtropical rainforest. At the New South Wales locality it grows at about 900m alt. among rocks (probably rhyolite) in moss gardens under tall Hoop Pines (Araucaria cunninghamiana). The soil at both localities is a brown loam.
Phenology: Flowering February to May.
Similar Species: Acianthus saxatilis has flowers like no other Australian species of Acianthus and is unlikely to be confused with any other Australian orchid. It can be immediately recognised by its relatively large leaf, large foliose floral bracts, large greenish to greenish and brown flowers, very broad cucullate dorsal sepal, broad lateral sepals held horizontally in a close pair directly beneath and subtending the labellum, spreading to upswept petals which have an attenuate apex and an ovate-lanceolate labellum which projects porrectly forwards from the column base. The labellum has a pair of prostrate tonsil-like glands at the base, an abbreviated central channel which extends about three-quarters of the labellum length and an acute to apiculate apex.