Arachnorchis actensis (Canberra Spider Orchid)

Advice to the Minister for the Environment and Heritage from the Threatened Species Scientific Committee (TSSC) on Amendments to the list of Threatened Species under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act)
6 June 2005

1. Scientific name, common name (where appropriate), major taxon group

Arachnorchis actensis (Canberra Spider Orchid)

The species was originally described as Caladenia actensis. A 2001 revision of the genus Caladenia resulted in the species being renamed Arachnorchis actensis.

2. Description

The Canberra Spider-orchid is a terrestrial orchid growing to between 4 and 9 centimetres. The greenish flowers are heavily marked with reddish crimson lines.

3. National context

The Canberra Spider-orchid is endemic to the Australian Capital Territory. It is currently only known from two populations of about 250 plants scattered over an area of a few hectares on the lower western slopes of Mt Ainslie and Mt Majura, in the Canberra Nature Park. It was previously recorded from sites at Aranda and Campbell, but no longer exists at either of these locations. Extensive surveys of suitable locations have failed to locate the species outside its previously known range. The Canberra Spider-orchid has recently been listed as an endangered species in the ACT under the Nature Conservation Act 1980.

EPBC Act criteria.

TSSC judges the species to be eligible for listing as critically endangered under the EPBC Act. The justification against the criteria is as follows:

Criterion 1 - Decline in numbers

In the last 40 years the Canberra Spider-orchid has been reduced from four populations to two extant populations totalling approximately 250 plants on the lower western slopes of Mt Ainslie (approximately 30 plants) and Mt Majura (approximately 220 plants), in the Canberra Nature Park. The two extinct populations were previously recorded at sites that have now been developed as part of the suburbs of Aranda, on the western slope of Black Mountain, and Campbell, on the slopes of Mt Ainslie.

Although the number of populations has declined from four to two populations over the last 40 years, there is no quantitative data available on the number of individuals from the two extinct populations. There is insufficient information to adequately quantify the decline in numbers during this period.

There is no quantitative data available against this criterion.

Criterion 2 - Geographic distribution

The Canberra Spider-orchid is known from two extant populations totalling approximately 250 plants with an area of occupancy of approximately five hectares on the lower western slope of Mt Ainslie (approximately 30 plants) and Mt Majura (approximately 220 plants), in the Canberra Nature Park. The species was previously recorded at a site that has now been developed as the suburb of Aranda, and at a second site on Mt Ainslie in the suburb of Campbell. It no longer exists at either of these locations.

Threats to the Canberra Spider-orchid include inappropriately timed fuel reduction burns, heavy vehicle damage from firebreak slashing, trampling and bicycle damage, encroachment of weeds and new road building, grazing by kangaroos and possible illegal collection.

The species occurs at only two locations, and two populations have been lost in the last 40 years.

The geographic distribution is precarious for the survival of the species and is very restricted.

Therefore, the species is eligible for listing as critically endangered under this criterion.

Criterion 3 - Population size and decline in numbers or distribution

The total population of the Canberra Spider-orchid is very low at approximately 250 plants. The number of populations has declined by 50% over the last 40 years. Threats to the Canberra Spider-orchid include inappropriately timed fuel reduction burns, heavy vehicle damage from firebreak slashing, grazing by kangaroos, possible illegal collection and activities related to its proximity to urban areas such as trampling and bicycle damage, encroachment of weeds and new road building.

The identified threats to these remaining populations are likely to lead to an ongoing decline in the number of individuals if measures are not taken to abate them.

Therefore, the species is eligible for listing as critically endangered under this criterion.

Criterion 4 - Population size

The total population size of the Canberra Spider-orchid is very low at approximately 250 plants.

Therefore, the species is eligible for listing as endangered under this criterion.

Criterion 5 - Probability of extinction in the wild

There is no quantitative data available against this criterion.

5. Conclusion

The Canberra Spider-orchid is currently known from two populations of about 250 plants with an area of occupancy of about five hectares on the lower western slopes of Mt Ainslie (about 30 plants) and Mt Majura (about 220 plants), in the Canberra Nature Park. The species was also previously recorded at a site that has now been developed as the suburb of Aranda, and at a second site on Mt Ainslie in the suburb of Campbell. It no longer exists at either of these locations.

The total population size of the Canberra Spider-orchid is very low at approximately 250 plants and the two existing populations are under continued pressure from activities related to its proximity to urban areas and possible inappropriate land management.

The species is eligible for listing as critically endangered under criteria 2 and 3.

6. Recommendation

TSSC recommends that the list referred to in section 178 of the EPBC Act be amended by including in the list in the critically endangered category:

Arachnorchis actensis (Canberra Spider-orchid)

Publications used to assess the nomination

Jones, D.L., and Clements, M. (1999). Caladenia actensis (Orchidaceae), a new species from the Australian Capital Territory. The Orchadian 12(11): 522-525.

Jones, D.L., Clements, M.A., Sharma, I.K., and Mackenzie, A.M. (2001). A new classification of Caladenia R.Br. (Orchidaceae). The Orchadian 13(9): 389-419.

Jones, D.L., Clements, M.A., Sharma, I.K., Mackenzie, A.M., and Molloy, B.P.J. (2002). Nomenclatural notes arising from studies into the Tribe Diurideae (Orchidaceae). The Orchadian 13(10): 437-468.

Conservation advice

The Canberra Spider-orchid only occurs in the ACT (Australian Capital Territory Natural Resource Management region). The species grows in transitional vegetation zones between open grassy woodland (dominated by Eucalyptus blakleyi, Eucalyptus melliodora and Eucalyptus pauciflora) and dry sclerophyll forest (dominated by Eucalyptus rossii). The soils are shallow gravelly brown clay loam of volcanic origin. Plants occur amongst a groundcover of grasses, forbs and low shrubs, often among rocks. It is currently known from only two small populations with a total population of approximately 250 plants on the lower western slopes of Mt Ainslie (approximately 30 plants) and Mt Majura (approximately 220 plants), within the Canberra Nature Park.

Key threats to the Canberra Spider-orchid include inappropriately timed fuel reduction burns, heavy vehicle damage from firebreak slashing, grazing by kangaroos, possible illegal collection and activities related to its proximity to urban areas such as trampling and bicycle damage, encroachment of weeds and new road building.

The priority recovery and threat abatement actions required for this species are:

  • protect the two sites where it is known to occur from direct physical disturbance and illegal collecting;
  • incorporate conservation measures, including management of fuel reduction burns or slashing, and weed control, into relevant Management Plans; and
  • undertake regular monitoring and further research to collate data on recruitment and better understand threats.

This list does not encompass all actions that may be of benefit to this species, but highlights those that are considered to be of the highest priority at the time of listing. Longer term issues that should be considered in broader landscape, regional and or recovery planning include establishing either an ex situ and/or additional population in the wild.

Priority for the development of recovery plan: Low. No Recovery Plan is currently in place for the Canberra Spider-orchid.