Pterostylis gibbosa (R.Br.) Illawarra Greenhood Orchid Recovery Plan

NSW National Parks and Wildlife Service, September 2002
ISBN 0 731 36905 X

Appendix 1 - Pterostylis gibbosa Species Profile

Illawarra Greenhood Orchid

Conservation Status

Pterostylis gibbosa is listed as an endangered species on Schedule 1 of the NSW Threatened Species Conservation Act 1995 and as an endangered species under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999.

Description

P. gibbosa (Orchidaceae) is a perennial terrestrial orchid. It belongs to the "greenhood" group of orchids that are characterised by green, hood-shaped flowers (Dressler 1981).

Leaves are elliptic to ovate in shape, 1.5 to 3.5 cm long, entire and arranged in a small basal rosette (Jones 1993).

Figure 4
Photo: R. Tunstall

The inflorescence consists of two to seven flowers held on a single scape (stalk) to 45 cm high with three to six closely sheathing stem leaves (Harden 1990).

Flowers are bright green with transparent areas in the galea (hood) and petals although light reddish-brown flowers have been observed (Jones & Clements 1997). The labelum (lip) is strongly exserted, brownish-black to black, with a deep central groove and thick basal lobe (Jones & Clements 1997).

Figure 5
Photo: L. Johnston

Distribution

P. gibbosa is presently known from five locations: three sites in the Illawarra (two sites at Yallah and one at Albion Park); one site near Nowra in the Shoalhaven; and one site at Milbrodale in the Hunter Valley.

The original or "type" specimen of P. gibbosa was collected in 1803 in western Sydney (NPWS 2000). Extensive surveys in recent years have failed to relocate the species in western Sydney and it is now considered likely to be extinct in that area (NPWS 2000).

Recorded occurrences in conservation reserves

P. gibbosa has been recorded from one conservation reserve, Worrigee Nature Reserve (previously part of Currambene State Forest), near Nowra.

Habitat

All known sub-populations of P. gibbosa occur in open forest or woodland on flat or gently sloping land with poorly drained soils.

In the Illawarra, P. gibbosa occurs on soils derived from Permian sedimentary rocks of the Berry formation at an altitude of 10 to 20 metres. Associated vegetation is woodland dominated by Eucalyptus tereticornis (Forest Red Gum) and Melaleuca decora (White Feather Honey-myrtle) with an open grassy understorey.

Near Nowra, P. gibbosa also occurs on soils derived from rocks of the Berry formation although at a slightly higher altitude of 20 to 30 metres. Associated vegetation is open forest dominated by Eucalyptus maculata (Spotted Gum) and Eucalyptus paniculata (Grey Ironbark) with an open grassy understorey.

The Milbrodale sub-population of P. gibbosa occurs at an elevation of 150 to 160 metres on soils derived from Triassic sedimentary rocks of the Narrabeen group. Associated vegetation is open woodland dominated by Eucalyptus crebra (Narrow-leaved Ironbark) and Eucalyptus molucanna (Grey Box), with Callitris endlicherii (Black Cypress Pine) present as a sub-dominant. The understorey at this location contains dense stands of the native shrub, Dodonaea cuneata.

Ecology

P. gibbosa is a deciduous orchid that is only visible above the ground between late summer and spring. Its rosette of leaves emerges from an underground tuberoid during late summer and autumn. A flower scape develops on mature plants over winter. Flowering occurs between September and October, after which the leaf rosette withers and seed capsules develop.

P. gibbosa flowers are thought to be pollinated by male fungus gnats (Genera Mycomya and Heteropterna) (NPWS 2000). The fruit is a dry, dehiscent, obovoid capsule containing thousands of minute, wind dispersed seeds (NPWS 2000).

P. gibbosa does not spread vegetatively to any great extent (NPWS 2000). A study by Sharma et al (2000) found a high mean viability rate (76%) for seeds collected from each known sub-population of the species.

P. gibbosa is capable of surviving occasional fire due to the regenerative capacity of the tuberoid (NPWS 2000).

Threats

Habitat loss from urban development and agriculture has greatly reduced the area of available habitat for the species. Further habitat loss will threaten the long-term viability of the species by further reducing population sizes and rendering extant sub-populations more vulnerable to stochastic events (NPWS 2000).

Frequent fires, particularly between March and November, are a potential threat to the species. Such fires will destroy above ground parts of the plant and may prevent flowering, seed set and the establishment of seedlings. Over time this may lead to the elimination of sub-populations. Frequent fire may also change the composition of surrounding vegetation by encouraging more fire tolerant species that may disadvantage P. gibbosa (NPWS 2000).

Fire exclusion may also threaten P. gibbosa as occasional fire may be necessary to provide conditions suitable for recruitment and growth of the species. The build up of leaf litter in the absence of fire will also increase the risk of high intensity fires that are more likely to kill tuberoids than low intensity fires (NPWS 2000).

Other potential threats to the species include: degradation of habitat through weed invasion, particularly by Lantana camara and Pittosporum undulatum; uncontrolled vehicular and pedestrian access to sites; and the collection of P. gibbosa by orchid enthusiasts (NPWS 2000).

Management

Future management must aim to increase the level of legislative protection afforded land upon which the species occurs. This can be facilitated on public and private land through a range of mechanisms including Voluntary Conservation Agreements, Joint Management Agreements, Property Management Plans etc.

Appropriate threat and habitat management practices include: weed removal to maintain suitable habitat; fencing to exclude vehicles and prevent rubbish dumping; and the establishment of appropriate grazing and fire regimes where necessary.

Further research and monitoring is required to gain a better understanding of the species and in particular, its response to different fire regimes.

Targeted survey is required to locate other extant populations of the species and so determine the full extent of the species distribution.

Recovery Plans

A recovery plan for P. gibbosa was approved in September 2002.

For Further Information contact

Threatened Species Unit Conservation Programs and Planning Division, Central Directorate NSW NPWS PO Box 1967, Hurstville NSW 2220 Phone 02 9585 6678. www.npws.nsw.gov.au

References

Dressler R.L. (1981) The Orchids: Natural History and Classification. Harvard University Press, New England.

Jones D.L. (1993) Pterostylis in Harden, G.J. (Ed.) Flora of New South Wales: Volume 4. New South Wales University Press, Kensington.

Jones D.L. & Clements M.A.(1997) Characterisation of Pterostylis gibbosa R.Br. (Orchidaceae) and description of P. saxicola, a rare new species from New South Wales. The Orchadian Vol. 12(3): 128-136.

National Parks and Wildlife (2000) Pterostylis gibbosa Draft Recovery Plan. NSW National Parks and Wildlife Service, Hurstville.

Sharma I.K, Clements M.A and Jones D.L (2000) Observations of high genetic variability in the endangered Australian terrestrial orchid Pterostylis gibbosa R. Br (Orchidaceae). Biochemical Systematics and Ecology Vol. 28: 651-663.

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