Pterostylis bicornis - endangered species listing

NSW Scientific Committee - final determination

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list the terrestrial orchid Pterostylis bicornis D.L.Jones & M.A.Clem. as an ENDANGERED SPECIES in Part 1 of Schedule 1 of the Act. Listing of Endangered species is provided for by Part 2 of the Act.


The Scientific Committee has found that:


1. Pterostylis bicornis D.L.Jones & M.A.Clem. (family Orchidaceae), commonly known as Horned Greenhood, was first described by Jones and Clements (1987) as a “small, slender terrestrial orchid with a rosette produced on a separate growth arising from the base of the floral scape. Rosette leaves 3–7, the lamina cordate, 3-7 mm x 3-5 mm, on broad petioles 2-4 mm long. Scape 6-10 cm tall, very slender, with 1-2 terminal flowers. Sterile bracts 3 or 4, to 10 mm x 3 mm, lanceloate, acuminate, sheathing at the base. Fertile bracts similar. Flowers 8-10 mm long, dark green and white; dorsal sepal 6-8 mm long, galeate, erect at the base then curved in the distal third, apex truncate or emarginate. Lateral sepals about 6 mm long, united in the basal two-thirds, the free segments closely embracing the galea and barely exceeding it, the lateral margins covering the petals. Petals 6-7 mm x 1.5 mm, curved, the apex produced into a filiform or slightly clavate tail 4-5 mm long which far exceeds the dorsal sepal. Labellum 3.4–4 mm x 1 mm, oblong, constricted in the distal quarter, curved sigmoidally, the basal appendage shortly branched. Column 3.5–4.5 mm long, erect, slender; wings about 1.5 mm long, their upper margin produced into a filiform point, the lower margins obtuse, sparsely ciliate. Anther cap about 0.8 mm long, obtuse, with a very short rostrum. Stigma about 1 mm x 0.5 mm, cordate, basal, the upper margins irregular. Polinia about 0.8 mm long, linear, mealy. Capsule not seen.”


2. Council of Heads of Australian Herbaria (CHAH 2007) recognizes the taxonomic name Pterostylis bicornis D.L.Jones & M.A.Clem. with Petrorchis bicornis (D.L.Jones & M.A.Clem.) D.L.Jones & M.A.Clem. as a synonym. Jones (2006) used the name Petrorchis bicornis. Pterostylis bicornis has affinities with both Pterostylis aphylla and Pterostylis parviflora but can be distinguished readily from these by the filiform tips on the petals (Jones & Clements 1987).


3. Pterostylis bicornis is listed nationally as a Vulnerable species under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999, and as a Vulnerable species in Queensland under the Nature Conservation (Wildlife) Regulation 2006 (Queensland) (TSSC 2008).


4. There is only one location for Pterostylis bicornis currently known in NSW, from near Woodenbong, in far northern NSW. Pterostylis bicornis also occurs in Queensland, at three locations along the NSW - Queensland border. In NSW, Pterostylis bicornis is very highly restricted. The area of occupancy was calculated to be 4 km2, based on 2x2 km grid cells, the scale recommended for assessing area of occupancy by IUCN (2010). The extent of occurrence was measured by a convex polygon encompassing the currently known sites, and extending this to the Queensland border in line with the sites within southern Queensland. This gives a more realistic measure of the extent of occurrence as most of the known occurrences for the species are in southern Queensland. This method gives the extent of occurrence as approximately 200 km2.


5. Pterostylis bicornis occurs in heathy forests or in heathlands. It grows in quite specific and limited habitat, in small humus pockets among moss and lichens in very shallow to skeletal soils over rock (Jones 2006; Mathieson pers. comm. Feb. 2011). It reproduces both sexually via seed and asexually, by forming tubers along the root system (Mathieson pers. comm. Feb. 2011). Flowering occurs from June to July (Jones & Clements 1987), although it has been seen flowering from mid-March through to mid-July, in the Queensland populations (Mathieson pers. comm. Feb 2011).


6. The number of mature individuals of Pterostylis bicornis in NSW is poorly known, although is considered to be very low. Benwell (pers. comm. 2010) estimated that there were less than 100 mature individuals, based on a 1999 general vegetation survey of the area where the population occurs.


7. The only known population of Pterostylis bicornis in NSW occurs in Toonumbar National Park. There is very little information on the current threats to the population of Pterostylis bicornis in NSW. The populations in Queensland are threatened by inappropriate fire regimes, particularly high fire frequency, and potentially by orchid collecting by plant hobbyists (Mathieson pers. comm. Feb. 2011). It would appear that the possibility of these threats affecting the NSW population is low, given the isolated location of the NSW population.


8. Pterostylis bicornis D.L.Jones & M.A.Clem. is not currently eligible to be listed as a Critically Endangered species. If further information becomes available, the species may need to be reassessed.


9. Pterostylis bicornis D.L.Jones & M.A.Clem. is eligible to be listed as an Endangered species as, in the opinion of the Scientific Committee, it is facing a very high risk of extinction in New South Wales in the near future as determined in accordance with the following criteria as prescribed by the Threatened Species Conservation Regulation 2010:


Clause 9 Low number of mature individuals of species


The total number of mature individuals of the species is observed, estimated or inferred to be:

(b) very low.


Dr Richard Major


Scientific Committee


Proposed Gazettal date: 09/12/11

Exhibition period: 09/12/11 – 03/02/12




Council of Heads of Australia Herbaria (CHAH) (2007) Review of Australian vascular plant names – report to Department of the Environment and Water Resources.


IUCN Standards and Petitions Subcommittee (2010) ‘Guidelines for Using the IUCN Red List Categories and Criteria Version 8.1.’ Prepared by the Standards and Petitions Subcommittee in March 2010.


Jones DL (2006) “A complete guide to native orchids of Australia.” (Reed New Holland, Sydney).


Jones DL, Clements MA (1987) New orchid taxa from South-eastern Queensland. Proceedings of the Royal Society of Queensland 98, 123-132.


Threatened Species Scientific Committee (2008). Commonwealth Conservation Advice on Pterostylis bicornis. [Online] Available at: (

Page last updated: 09 December 2011