Acianthus fornicatus
Plant: Erect herb 6-30 cm tall.
Stem: Straight, terete, 2-4 cm long, green or greenish red, glabrous.
Cataphyll: Sheathing, tubular, 4-7 mm long, membranaceous, 1-nerved, hardly or not expanded distally, the apex acute.
Leaf: Sessile, entire or rarely weakly 3-lobed, broadly ovate to ovate-elliptic, 1.6-5.8 cm long, 1.4-3.6 cm broad, dark green above, reddish purple beneath, the base deeply cordate, with slightly imbricate or weakly divergent basal lobes, the apex abruptly acuminate and frequently minutely apiculate or rarely subacute, the margin entire or sometimes weakly undulate.
Peduncle: 3.5-13.5 cm long.
Inflorescence: Slender, 4.5-25 cm long, subdensely 3- to 10-flowered.
Bracts: Ovate, elliptic-ovate or sometimes oblong-ovate, 3-5.5 mm long, 1.3-3.5 mm broad, 3-nerved, dark green, with a few scattered, oblong-elliptic idioblasts distally, the base broadly rounded or cuneate, the apex gradually acuminate or narrowly acute.
Ovary: Briefly pedicellate, cylindrical-clavate, 5-10 mm long, weakly 6-ribbed.
Flowers: Ascending (sometimes weakly so), the outer perianth segments somewhat translucent, pale greenish red to greenish purple, frequently with reddish markings along the nerves, or rarely pale green, the labellum pale to dark green with the lateral margins and apex suffused with dark reddish purple, the column greenish white.
Dorsal Sepal: arched above column, broadly ovate, ovate-elliptic, or elliptic, 5-14 mm long, 3.5-6 mm broad, 3-nerved, strongly cucullate proximally, broadly rounded at base, abruptly acuminate and manifestly apiculate at apex, the apicule subulate or setiform, 1.5-4 (-6) mm long.
Lateral Sepals: Porrect, weakly appressed to labellum, frequently slightly deflexed and weakly divergent from each other distally, linear-lanceolate or linear-ligulate, 6-12 mm long, (0.6-) 0.8-1.3 mm broad, 1-nerved, often abruptly constricted subapically, manifestly apiculate at apex, the apicule setiform, 1.5-3 mm long.
Lateral petals: Weakly spreading, lanceolate, slightly oblique, 2.5-5 mm long, 0.5-1 mm broad, 1-nerved, very gradually acuminate at apex.
Labellum: Porrect or weakly reclined, very briefly clawed, moderately sigmoid, entire, 3.5-7 mm long, 1.8-4 mm broad, 3-nerved, the blade oblong-ovate or oblong-elliptic, deeply concave proximally, somewhat porcate laterally, broadly cuneate or truncate at base, abruptly acuminate or acute at apex, the lateral margins gradually becoming strongly revolute medially, subentire, erose, or sometimes irregularly denticulate, the disk with 2 large calli at base, the proximal portion finely reticulate medially throughout an oblong or oblong-cuneate region, the distal portion laxly to subdensely papillose laterally, the calli partially embracing column base, erect, clavate-falcate, gradually increasing in height distally and weakly confluent with each other apically.
Column: Arcuate, terete, 2.8- 3.5 mm long, unappendaged, prominently gibbous at base, strongly dilated at apex; anther locules suborbicular, 0.6-0.8 mm across; pollinia strongly 2-lobed, the lobes more or less clavate or pyriform, relatively firm, unequal, 0.3-0.5 mm long, the viscidia 2, broadly ovate or transversely ovate, 0.2-0.3 mm across; rostellum porrect, relatively long, the anterior margin weakly tri-denticulate; stigma small, suborbicular, shallowly recessed.
Capsule: Oblong-obovoid or oblong-ellipsoid, 8-12 mm long, 3-4 mm in diameter.
Type: AUSTRALIA. Port Jackson, May 1802(A), R. Brown s. n. (lectoype designated by Clements in Austral. Orchid Res. 1: 9. 1989: bm!; isolectotypes: ad, bm!, e, k (photo no!), l!, le (photo ny), p!)
Distribution: Endemic to Australia and widely distributed in coastal regions from the Endeavor River in the southeastern Cape York Peninsula of Queensland to the extreme southeastern part of New South Wales.
Ecology: Acianthus fornicatus grows in open forest, heathlands or scrub, often under low shrubs or herbs, in light to moderate shade. It is frequently found on the walls of small gullies, along stream banks or roadcuts, often in rocky areas, and may be locally abundant. Jones (1988) suggests that Acianthus fornicatus favors sandy soils, but it is found on other soil types as well. The species has been collected from near sea level to approximately 1700 m elevation. The species does not appear to be autogamic and is probably pollinated by small Diptera.
Phenology: Flowering April through October, and capsules from May to November.
Similar Species: Acianthus fornicatus is the most common representative of section Acianthus, and the species is moderately polymorphic throughout its range. This variability was first noted by Rupp (1944) who commented that coastal colonies consistently produce larger flowers than do inland populations. A number of segregate species have recently been proposed by Jones (1991) on the basis of differences in stature, floral orientation, size, coloration, and labellar morphology, but the variation in size appears to be continuous rather than disjunct. After examining the extensive holdings of A. fornicatus, sensu lato, at ad, bri, nsw, and Perth, and the excellent drawings and photographs of A. apprimus, A. borealis, A. collinus, and A. exiguus in the protologues, it is evident that these taxa are insufficiently distinct to warrant formal taxonomic recognition. In addition to the four taxa proposed by Jones, A. ledwardii Rupp is here considered as a synonym of A. fornicatus.