Dunsborough Spider Orchid (Caladenia viridescens) recovery plan
Government of Western Australia, Department of Environment and Conservation
Department of the Environment, Water, Heritage and the Arts 2008
About the plan
Scientific Name: Caladenia viridescens
Common Name: Dunsborough spider orchid
Flowering Period: September - October
DEC Region: South West
DEC District: Blackwood
South West Region Threatened Flora and Communities Recovery Team
Illustrations and/or further information: Brown, A., Thomson-Dans, C. and Marchant, N. (Eds) (1998) Western Australia's Threatened Flora. Department of Conservation and Land Management, Perth; Hoffman, N. and Brown, A. (1992) Orchids of South-west Australia. University of Western Australia Press. Perth; Hopper, S.D. and Brown, A.P. (2001) Contributions to Western Australian Orchidology:2. New taxa and circumscriptions in Caladenia (Spider, Fairy and Dragon orchids of Western Australia). Nuytsia 14(1/2), 27-308.
Caladenia viridescens was declared as Rare Flora under the Western Australian Wildlife Conservation Act 1950 in September 1992 and is currently ranked Critically Endangered (CR) in Western Australia under World Conservation Union (IUCN 2001) Red List criteria B1ab(iii,v)+2ab(iii,v); C2a(i) and D due to its limited distribution, severe fragmentation of populations and continuing decline in the quality of habitat and number of mature individuals. The main ongoing threats are further habitat degradation and inappropriate fire regimes. The species is listed as Endangered under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act).
Caladenia viridescens stands from 25 to 40cm high, and has a single leaf, 15-20cm long and 5-8mm wide. It displays one to three flowers, which are pale green, stiffly held, and which have a narrow labellum. The flowers are similar in size and shape to those of C. busselliana and also the common C. paludosa (Swamp Spider Orchid). C. viridescens differs from C. busselliana, its nearest relative, in its green colouration, its dark maroon fringe and apex, and shorter, wider clubs on the sepals (Hoffman and Brown 1992). Although the plants are perennial herbs, they are reduced to a below-ground storage organ (tuber) in summer, re-emerging in autumn and flowering from mid-September to late October.
Caladenia viridescens occurs over a linear range of 12km near the northern end of the Leeuwin-Naturaliste Ridge. It grows on well-drained lateritic sandy loam soils in marri and peppermint woodlands with C. brownii or coastal heath with Calothamnus graniticus subsp. graniticus, Hakea trifurcata and many other Caladenia species, and occasionally occurs in the same swampy areas that C. busselliana favours.
Guide for decision-makers:
Section 1 provides details of current and possible future threats. Developments in the immediate vicinity of populations or within the area defined as habitat critical for survival require assessment. Any on-ground works (clearing, firebreaks, roadworks, spraying of herbicides, burning, drainage etc) in the immediate vicinity of Caladenia viridescens will require assessment. Proponents should demonstrate that on-ground works will not have an impact on the species, or on its habitat or potential habitat.
Habitat critical to the survival of the species, and important populations:
Habitat critical to the survival of the species includes the area of occupancy of important populations; areas of similar habitat surrounding important populations i.e. well-drained lateritic sandy loam soils or winter-wet swamps in jarrah, marri and peppermint woodlands or coastal heath (these provide potential habitat for natural expansion); and additional occurrences of similar habitat that may contain important populations of the species or be suitable for future translocations or other recovery actions intended to create important populations. All population are considered important for the long-term recovery and survival of the species.
Benefits to other species/ecological communities:
Recovery actions implemented to improve the quality or security of the habitat of Caladenia viridescens will also improve the status of the threatened giant spider orchid (C. excelsa) and Bussell's spider orchid (C. busselliana), which occurs in the habitat of C. viridescens at Population 4.
This plan is fully consistent with the aims and recommendations of the Convention on Biological Diversity, ratified by Australia in June 1993, and will assist in implementing Australia's responsibilities under that Convention. Although the taxon is listed under the United Nations Environment Programme World Conservation Monitoring Centre (UNEP-WCMC) Convention on International Trade in Endangered Species (CITES) this IRP does not affect Australia's obligations under international agreements.
Role and interests of Indigenous people:
Involvement of the Indigenous community is being sought through the advice of the Department of Indigenous Affairs to determine whether there are any issues or interests identified in the plan. A search of the Department of Indigenous Affairs Aboriginal Heritage Sites Register has identified that there are no sites of Aboriginal significance at or near populations of the species covered by this IRP. Where no role is identified for the Indigenous community associated with this species in the development of the recovery plan, opportunities may exist through cultural interpretation and awareness of the species. Indigenous involvement in the implementation of recovery actions will be encouraged.
Social and economic impacts:
The implementation of this recovery plan has the potential to have some social and economic impact, as some populations are located on Shire and unvested reserves, and State Forest, and this is discussed under recovery actions.
Evaluation of the Plans Performance:
DEC, in conjunction with the Recovery Team will evaluate the performance of this IRP. The plan is to be reviewed within five years.
Completed Recovery Actions:
The following recovery actions have been implemented:
- Relevant land managers have been made aware of the location and threatened status of the species.
- Declared Rare Fauna (DRF) markers have been installed at all roadside populations.
- Habitat restoration measures including deep-ripping, rubbish removal and weed control have been undertaken at Population 4. A track at Population 4 has also been closed to help prevent illegal rubbish dumping.
- Spot spraying of weeds has been carried out as appropriate.
- The habitat of Population 4 has been fenced to exclude grazing.
- Staff from Botanic Garden and Parks Authority (BGPA) collected seed from Population 1 in 2001. They also collected seed and fungi in 2002. This is stored in the BGPA's plant science lab at â196Â°C.
- BGPA staff have assessed material from Caladenia viridescens to determine the genetic distinctiveness of the species.
- Germination trials of Caladenia viridescens have been carried out by BGPA staff and germination rates of around 60% have been achieved.
- A research burn was undertaken in December 1999 to investigate how the species responds to fire. Monitoring of this trial is ongoing. Population 3b was burnt in Autumn 2002 and the area around Population 1b was burnt in May 2004.
- An information sheet that describes and illustrates the species has been produced and distributed.
- A new population (Population 6) was located during surveys for additional populations undertaken in 1999-2000.
- The species was promoted through threatened flora displays at local wildflower shows and threatened flora field days.
- A review of historical rainfall data was undertaken in 2001 to identify any correlation between rainfall patterns and orchid flowering.
The objective of this Interim Recovery Plan is to abate identified threats and maintain or enhance in situ populations to ensure the long-term preservation of the species in the wild.
Criteria for success:
The number of individuals within populations and/or the number of populations have increased by 10 percent or more over the five years of the plan.
Criteria for failure:
The number of individuals within populations and/or the number of populations have decreased by 10 percent or more over the five years of the plan.
- Coordinate recovery actions
- Stimulate seed set
- Collect seed and fungal material
- Monitor populations
- Conduct further surveys
- Complete and implement the fire management strategy
- Obtain biological and ecological information
- Undertake translocation
- Stimulate flowering
- Map habitat critical to survival
- Continue weed control
- Control rabbits
- Liaise with land managers
- Seek to increase security of Population 4
- Promote awareness
- Rehabilitate habitat as required
- Review this Plan