Biodiversity

Species Profile and Threats Database


For information to assist proponents in referral, environmental assessments and compliance issues, refer to the Policy Statements and Guidelines (where available), the Conservation Advice (where available) or the Listing Advice (where available).
 
In addition, proponents and land managers should refer to the Recovery Plan (where available) or the Conservation Advice (where available) for recovery, mitigation and conservation information.

EPBC Act Listing Status Listed as Endangered as Caladenia excelsa
Listing and Conservation Advices Commonwealth Conservation Advice on Caladenia excelsa (Giant Spider-orchid) (Threatened Species Scientific Committee, 2008d) [Conservation Advice].
 
Recovery Plan Decision Recovery Plan not required, included on the Not Commenced List (1/11/2009).
 
Adopted/Made Recovery Plans
Policy Statements and Guidelines Draft survey guidelines for Australia's threatened orchids (Department of the Environment, 2013b) [Admin Guideline].
 
Federal Register of
    Legislative Instruments
Declaration under s178, s181, and s183 of the Environment Protection and Biodiversity Conservation Act 1999 - List of threatened species, List of threatened ecological communities and List of threatening processes (Commonwealth of Australia, 2000) [Legislative Instrument] as Caladenia excelsa.
 
Amendment to the list of threatened species under section 178 of the Environment Protection and Biodiversity Conservation Act 1999 (11/04/2007) (Commonwealth of Australia, 2007f) [Legislative Instrument] as Caladenia excelsa.
 
State Government
    Documents and Websites
WA:Declared Rare and Poorly Known Flora in the Central Forest Region. Part 2 (Williams, K., A. Horan, S. Wood & A. Webb, 2001) [State Species Management Plan].
State Listing Status
WA: Listed as Endangered (Wildlife Conservation Act 1950 (Western Australia): September 2013) as Caladenia excelsa
Scientific name Caladenia excelsa [56717]
Family Orchidaceae:Orchidales:Liliopsida:Magnoliophyta:Plantae
Species author Hopper & A.P.Br.
Infraspecies author  
Reference Hopper, S.D. & Brown, A.P. (2001), Nuytsia 14(1/2): 68-71
Other names Caladenia sp. 8 (Leeuwin-Naturaliste N.P.) [24388]
Caladenia excelsa Hopper & Brown ms. [67273]
Caladenia excelsa Hopper & A.P.Brown ms. [67366]
Caladenia sp. Leeuwin-Naturaliste (S.D.Hopper 4670) [68655]
Arachnorchis excelsa [78686]
Distribution map Species Distribution Map

This is an indicative distribution map of the present distribution of the species based on best available knowledge. See map caveat for more information.

Illustrations Google Images

Scientific name: Caladenia excelsa

Common name: Giant Spider-orchid

Caladenia excelsa is conventionally accepted (CHAH 2010).

The Giant Spider-orchid is a tuberous, perennial herb that is one of the tallest spider orchids in Western Australia with stems 45–90 cm tall, usually with 1–2 flowers. The flowers are 15–30 cm long by 7–15 cm wide, cream coloured and marked with maroon stripes. The leaves are 20–35 cm long and 6–12 mm wide. The dorsal sepal (top petal) is erect initially, but then arches backward and becomes pendulous. Petals (9.5–15 cm long by 3–5 mm wide) and lateral sepals (13–20 cm long by 12–17 mm wide) narrow at 2–2.5 cm to slender elongate pendulous filaments. The labellum (lowest large petal, which is 25–35 mm long by 12–17 mm wide) has cream-coloured lamina (flat blades) at the base becoming maroon toward the apex and a marginal fringe 5–10 mm long (Williams et al. 2001).

The Giant Spider-orchid is distributed between Yallingup and Karridale along the Leeuwin-Naturaliste Ridge, approximately 300 km south of Perth, in the South West Forest Region of Western Australia (Atkins 1998; Williams et al. 2001). The species is known from 26 locations (WA DEC 2007).

The Giant Spider-orchid's extent of occurrence is calculated to be 124.4 km². There are insufficient data to indicate a decline in extent of occurrence of this restricted species (WA DEC 2007).

The Giant Spider-orchid has an estimated total population of 257 plants across 26 subpopulations (WA DEC 2007). These subpopulations are small (the largest was known to have 37 plants in the year 2000), and in some cases made up of single plants. Some subpopulations have historically been recorded as having no plants. For a summary of all known subpopulations, including number of plants, survey history, size, condition and known and potential threats, see WA DEC 2007. 

Ten Giant Spider-orchid subpopulations occur in Leeuwin Naturaliste National Park which is part of the Western Australia Department of Environment and Conservation formal conservation reserve system. National parks are managed for the conservation of flora and fauna, but not specifically for the species (WA DEC 2007).

The Giant Spider-orchid grows on hilltops, slopes, swales in deep white, grey or brown sands or sandy loam of the Leeuwin-Naturaliste Ridge. Associated vegetation includes dense low shrubs in Banksia (Banksia spp.), Jarrah (Eucalyptus marginata) and Marri (Corymbia calophylla) woodlands (Hopper & Brown 2001b; Williams et al, 2001).

The Giant Spider-orchid is dormant over summer and has a growing phase from April through to late November. Following the first seasonal rains, the tuber sprouts and a single leaf appears above ground. During late autumn-winter, the replacement tuber, which is essential for the plant's survival post-flowering, is initiated and continues to develop until late in the growing season. Further research is needed to understand the interactions between leaves and tubers as 'sinks' for resources. It seems likely that tubers must reach a critical size to sustain dormancy throughout the summer (Patten et al. 2005).

The Giant Spider-orchid flowers from late September to early November (Brown et al. 1998; Williams et al. 2001). Summer fires do not stimulate flowering of this species. Plants flower for approximately two weeks or until pollination occurs, after which flowers collapse and if pollination is successful a seed capsule develops. The capsule swells as seeds mature, and this can take from six to eight weeks to develop depending on climatic conditions. If temperatures are higher, then average seeds may mature faster. Prior to seeds being released the green capsule turns yellow and then brown. Small slits develop in the capsule from which the seed is dispersed. Up to 30 000 seeds can be produced in the one capsule. Not all plants will produce flowers in any one year. The proportion of flowering to non-flowering individuals is influenced by environmental conditions including the amount of rainfall during winter and spring (Patten et al. 2005).

Seeds will remain dormant in the soil over summer until the break of the season the following year. Once wet, the seeds imbibe water and the seed coat splits. At this point, infection by a suitable fungus is required for germination to occur which will result in a protocorm and the development of a seedling. Not all seedlings will mature, as those that fail to produce a tuber will not survive dry summer conditions. If no fungus is present, seeds remain in the soil throughout the growing season and those that are not eaten are killed by dry summer conditions. Orchid seedlings are very small for the first growing season and are difficult to locate. Leaves are typically less than 20 mm long and only a few millimeters wide. It appears that leaf and tuber size will then increase over the next two to five years until they become adult plants capable of flowering (Patten et al. 2005).

At the ecotones linking their respective habitats, the Giant Spider-orchid occasionally grows and hybridises with Caladenia longicauda (Hopper & Brown 2001b).

The Giant Spider-orchid is distinguished from Caladenia longicauda by the former's red-tipped labellum (lip) and long, hanging petals and sepals (Atkins 1998; Brown et al. 1998; Hoffman & Brown 1998; Williams et al. 2001). Detectability is optimum during the species' flowering period from late September to November (Brown et al. 1998).

Several populations of the Giant Spider-orchid occur on land where there is risk of accidental damage, such as road verges, gravel reserve, recreation reserves, water reserve, and private property. Many of the subpopulations are located on or near tracks or firebreaks and are at risk from maintenance operations. Tracks and firebreaks are likely to be used during prescribed burning and this could potentially affect the orchids.

Research has indicated that adult plants are most vulnerable to fire during the vegetative stage (April-early November) when replacing their parent tuber(s). If control burns are considered for the area, it is strongly recommended that they should not take place from April to early November. Late November is the recommended time for burning (WA DEC 2007).

Subpopulations 2 and 3 are in disturbed habitat which is heavily affected by weedy grasses. Subpopulation 19f has been affected by kangaroo grazing, however the landowners are taking preventative measures — hanging wind-chimes/reflectors in trees and some fencing (WA DEC 2007)

Williams and colleagues (2001) recommend monitoring and fire for habitat quality maintenance. Landowners have been made aware of the occurrence of the Giant Spider-orchid on their property. Where appropriate, road markers have been installed (WA DEC 2007).

Management documents relevant to the Giant Spider-orchid are at the start of the profile.

The following table lists known and perceived threats to this species. Threats are based on the International Union for Conservation of Nature and Natural Resources (IUCN) threat classification version 1.1.

Threat Class Threatening Species References
Ecosystem/Community Stresses:Indirect Ecosystem Effects:Restricted geographical distribution (area of occupancy and extent of occurrence) Caladenia excelsa in Species Profile and Threats (SPRAT) database (Department of the Environment and Heritage (DEH), 2006ea) [Internet].
Human Intrusions and Disturbance:Human Intrusions and Disturbance:Mechanical disturbance during construction, maintanance or recreational activities Caladenia excelsa in Species Profile and Threats (SPRAT) database (Department of the Environment and Heritage (DEH), 2006ea) [Internet].
Human Intrusions and Disturbance:Recreational Activities:Disturbance, especially from human recreational activities and development Declared Rare and Poorly Known Flora in the Central Forest Region. Part 2 (Williams, K., A. Horan, S. Wood & A. Webb, 2001) [State Species Management Plan].
Invasive and Other Problematic Species and Genes:Invasive Non-Native/Alien Species:Competition and/or habitat degradation by weeds Commonwealth Conservation Advice on Caladenia excelsa (Giant Spider-orchid) (Threatened Species Scientific Committee, 2008d) [Conservation Advice].
Invasive and Other Problematic Species and Genes:Problematic Native Species:Competition, predation and/or habitat degradation by kangaroos and wallabies Commonwealth Conservation Advice on Caladenia excelsa (Giant Spider-orchid) (Threatened Species Scientific Committee, 2008d) [Conservation Advice].
Natural System Modifications:Fire and Fire Suppression:Inappropriate and/or changed fire regimes (frequency, timing, intensity) Commonwealth Conservation Advice on Caladenia excelsa (Giant Spider-orchid) (Threatened Species Scientific Committee, 2008d) [Conservation Advice].
Natural System Modifications:Fire and Fire Suppression:Inappropriate prescribed regimes and/or vegetation management to control fire regimes Declared Rare and Poorly Known Flora in the Central Forest Region. Part 2 (Williams, K., A. Horan, S. Wood & A. Webb, 2001) [State Species Management Plan].
Species Stresses:Indirect Species Effects:Low numbers of individuals Caladenia excelsa in Species Profile and Threats (SPRAT) database (Department of the Environment and Heritage (DEH), 2006ea) [Internet].
Declared Rare and Poorly Known Flora in the Central Forest Region. Part 2 (Williams, K., A. Horan, S. Wood & A. Webb, 2001) [State Species Management Plan].

Atkins, K.J. (1998). Conservation Statements for threatened flora within the regional forest agreement region for Western Australia. Page(s) 1-95. Western Australia: Department of Conservation and Land Management.

Brown, A., C. Thomson-Dans & N. Marchant, eds. (1998). Western Australia's Threatened Flora. Como, Western Australia: Department of Conservation and Land Management.

Council of Heads of Australasian Herbaria (CHAH) (2010). Australian Plant Census. [Online]. Australian National Herbarium, Australian National Botanic Gardens and Australian Biological Resources Study . Available from: http://www.anbg.gov.au/chah/apc/.

Hoffman, N. & A. Brown (1992). Orchids of South-west Australia 2nd edn. Nedlands, Western Australia: University of Western Australia Press.

Hopper, S.D. & A.P. Brown (2001b). Contributions to Western Australian orchidology: 2. New taxa and circumscriptions in Caladenia (Spider, Fairy and Dragon Orchids of Western Australia). Nuytsia. 14(1/2):27-314. Perth, Western Australia: Department of Conservation & Land Management.

Patten, J., A.P. Webb & A. Batty (2005). Bussell's Spider Orchid (Caladenia busselliana) Interim Recovery Plan No. 214, 2005-2010. Western Australia, Department of Conservation and Land Management.

Western Australia Department of Environment and Conservation (WA DEC) (2007). Records held in DEC's Declared Flora Database and rare flora files. Perth, Western Australia: Department of Environment and Conservation.

Williams, K., A. Horan, S. Wood & A. Webb (2001). Declared Rare and Poorly Known Flora in the Central Forest Region. Part 2. [Online]. Western Australian Wildlife Management Program No. 33. Department of Conservation and Land Management. Available from: http://www.dpaw.wa.gov.au/plants-and-animals/threatened-species-and-communities/threatened-plants.

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This database is designed to provide statutory, biological and ecological information on species and ecological communities, migratory species, marine species, and species and species products subject to international trade and commercial use protected under the Environment Protection and Biodiversity Conservation Act 1999 (the EPBC Act). It has been compiled from a range of sources including listing advice, recovery plans, published literature and individual experts. While reasonable efforts have been made to ensure the accuracy of the information, no guarantee is given, nor responsibility taken, by the Commonwealth for its accuracy, currency or completeness. The Commonwealth does not accept any responsibility for any loss or damage that may be occasioned directly or indirectly through the use of, or reliance on, the information contained in this database. The information contained in this database does not necessarily represent the views of the Commonwealth. This database is not intended to be a complete source of information on the matters it deals with. Individuals and organisations should consider all the available information, including that available from other sources, in deciding whether there is a need to make a referral or apply for a permit or exemption under the EPBC Act.

Citation: Department of the Environment (2014). Caladenia excelsa in Species Profile and Threats Database, Department of the Environment, Canberra. Available from: http://www.environment.gov.au/sprat. Accessed Fri, 18 Apr 2014 09:12:29 +1000.