Pterostylis ventricosa an orchid - critically 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 orchid Pterostylis ventricosa (D.L. Jones) G.N. Backh. as a CRITICALLY ENDANGERED SPEICES in Part 1 of Schedule 1A of the Act. Listing of Critically Endangered species is provided for by Part 2 of the Act.


The Scientific Committee has found that:


1. Pterostylis ventricosa (D.L. Jones) G.N. Backh. is the name currently accepted in NSW for this recently described species. The species was published as Speculantha ventricosa D.L. Jones (Jones 2008).


2. Pterostylis ventricosa (D.L. Jones) G.N. Backh. is described by Jones (2008) under the name of Speculantha ventricosa D.L. Jones as a ‘glabrous, tuberous, terrestrial herb. Plants 8-30 cm tall, not elongating in fruit. Rosettes just emerging at anthesis, 1-2, borne on lateral growths from the base of the scape or on sterile plants. Rosette leaves spreading, 4-9 per rosette; lamina ovate to sagittate, 3-12 mm long, 3-6 mm wide, dull green; margins entire; apex acute to apiculate; petioles 3- 8 mm long, very slender, narrowly winged. Scape slender, wiry, 1-6-flowered. Sterile bracts closely sheathing or spreading and foliose, 3-5, ovate-lanceolate, 5-12 mm long, 2-5 mm wide, acuminate. Fertile bracts closely sheathing, ovate, 3-6 mm long, 2-4 mm wide, acuminate. Flowers well spaced, 1-3 open at once, 10-13 mm long, 4.5-5.5 mm wide, green and white towards the base, bright red-brown distally, somewhat shiny, swollen at the base and narrowing distally; galea strongly inflated at base, erect before curving forwards in a semi-circle; petals longer than the dorsal sepal, smooth (non-scabrous). Dorsal sepal broadly ovate-lanceolate when flattened, 13-16 mm long, 5-8 mm wide, inflated at the base then tapered to apex, boldly striped, acute to apiculate, smooth. Lateral sepals erect, closely embracing the galea; sinus curved smoothly inwards, the area below bulging when viewed from the side, deeply notched at the centre, margins sloping obliquely upwards; conjoined part 6-8 mm long, 5-7 mm wide, narrowed to 2 mm wide at the base; free points erect, 2.5-3.5 mm long, linear-tapered, just reaching above the top of the galea. Petals broadly oblong, 10-13 mm long, 2.5-3 mm wide, strongly falcate, dark brown striped with white, acute; flange c. 1 mm across, broadly deltate, obtuse. Labellum erect, the tip visible through sinus in the set position, curved forwards near apex, dark red-brown and white. Labellum lamina broadly oblong-elliptical, 4.5-5 mm long, 2-2.3 mm wide, obtuse; basal appendage decurved, c. 1.3 mm long, broadest at the base; apex trifid, erect. Callus a raised, central, dark red brown ridge c. 0.3 mm across. Column 6-8 mm long, curved away from the ovary at 50° at the base then erect, red brown and white. Column wings c. 2.4 mm long; basal lobe broadly deltate, c. 1 mm long, c. 0.7 mm wide, brown, at an angle 50°; apex broadly obtuse; inner margins adorned sparsely with short, white cilia; mid-section c. 1 mm long, brown; apical lobe obliquely erect or curved, filiform, c. 0.7 mm long, acute. Anther c. 1.3 mm long, obtuse. Pollinia linear, c. 1.2 mm long, yellow, mealy. Stigma situated below the middle, broadly cordate, c. 2.2 mm long, c. 2.2 mm wide, prominently raised. Capsules erect, obovoid to ellipsoid, 9-12 mm long, 3-4 mm wide.’


3. Pterostylis ventricosa grows in open areas within tall eucalypt forest with a dense heathy understorey (Jones 2008). It is also found in open disturbed sites such as road verges and at one location, beneath a powerline easement.


4. Pterostylis ventricosa is known from four populations at St Georges Basin and Sussex Inlet, south of Nowra on the NSW south coast. The single population at St Georges Basin is located at a distance of c.10 km from the three Sussex Inlet populations. The geographic distribution of Pterostylis ventricosa is very highly restricted. The extent of occurrence is 26 km2, measured using a minimum convex polygon covering the known distribution, the recommended measure for extent of occurrence in the IUCN (2010) guidelines. The area of occupancy (AOO) is estimated to be 16 km² based on a 2 x 2 km grid, the scale recommended by IUCN (2010). The actual on ground area of occupancy is likely to be less.


5. The number of mature individuals is considered to be low. There were approximately 1200 plants, estimated from surveys carried out at various times from 2007 to 2010. Pterostylis ventricosa is currently known from areas of private land and land reserved for conservation purposes. The two largest populations, one at St Georges Basin and one at Sussex Inlet, are located on estates of private land that are currently zoned as rural. The current zoning does not entitle landowners to build on the blocks, but future rezoning may give this entitlement. Two smaller populations, comprising a total of less than 10% of the known plants, are within Conjola National Park.


6. Threats to the populations of Pterostylis ventricosa include clearing of habitat, disturbance of habitat by vehicles and domestic animals and stock, and illegal collection of the orchid. The two largest populations of Pterostylis ventricosa that are located on private land are currently located in habitat that is in a near natural state. However, at the St Georges Basin population, nearby occupied blocks have domestic animals such as horses and goats that may be a threat to the orchid habitat. The largest population at Sussex Inlet is on land unoccupied by residential dwellings, but bordered by rural/residential properties. Future rezoning of this land may lead to clearing for residential development. One of the populations located in Conjola National Park occupies habitat on a power line easement. Maintenance activities beneath the power line could pose a threat to the orchid, particularly if it is carried out when the orchid is at a vulnerable life stage, eg. when it is present above ground as a flowering stalk or a rosette. ‘Clearing of native vegetation’ is listed as a Key Threatening Process under the Threatened Species Conservation Act 1995.


7. Pterostylis ventricosa (D.L. Jones) G.N. Backh. is eligible to be listed as a Critically Endangered species as, in the opinion of the Scientific Committee, it is facing an extremely high risk of extinction in New South Wales in the immediate future as determined in accordance with the following criteria as prescribed by the Threatened Species Conservation Regulation 2010:


Clause 7 Restricted geographic distribution and other conditions

The geographic distribution of the species is estimated or inferred to be:

(a) very highly restricted,


(d) a projected or continuing decline is observed, estimated or inferred in either of the key indicators:

(a) an index of abundance appropriate to the taxon, or

(b) geographic distribution, habitat quality or diversity, or genetic diversity.


Dr Richard Major


Scientific Committee


Proposed Gazettal date: 08/07/11

Exhibition period: 08/07/11 – 02/09/11




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 (2008) Two threatened new species of Speculantha (Orchidaceae) from south-eastern Australia. The Orchadian 16, 30-35.

Page last updated: 08 July 2011