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National recovery plan for Arachnorchis macroclavia (syn. Caladenia macroclavia) (Large - club Spider - orchid)

Doug Bickerton
National Parks and Wildlife SA
In partnership with Threatened Plant Action Group, February 2003

Note: This publication has been superseded by the Recovery Plan for Twelve Threatened Orchids in the Lofty Block Region of South Australia 2010

Recovery Plan for Arachnorchis macroclavia cover page

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Part A: Information Components (continued)

Critical Habitat

Arachnorchis macroclavia is found in mallee woodland and grassy mallee woodland with sandy loam soils over limestone. Mallee species such as Eucalyptus gracilis, E. socialis and E.incrassata dominate the canopy at all five confirmed sites. A well-developed shrub layer is present at Agery, Muloowurtie and Pt Vincent. Species such as Alyxia buxifolia and Melaleuca uncinata and chenopods dominate the understorey at Agery and Muloowurtie. The Pt Vincent site comprises many thickets of Melaleuca uncinata and large open areas of sedges. The understorey at the Pt Julia site has a predominance of sedges, while at Mona both grasses and sedges dominate. See Appendix 1 for a more detailed list of associated plant species. Although mallee woodland and grassland were once widespread across Yorke Peninsula, it survives mostly in small remnant blocks and along roadsides.

 The specific fungal endophyte that the orchid requires for nutrient has not been isolated and identified, and neither has the primary pollinator species, although it is likely to be a Thynnid wasp.

Threats

The main direct threats to Arachnorchis macroclavia and its critical habitat include grazing by vertebrate animals, competition from weeds, habitat damage by vehicles, dumping of soil or rubbish, herbicide drift, clearance of habitat for agriculture and road works. These activities have caused a decline in the area and quality of the orchid's critical habitat, and as a result, sub-populations are now very small (Table 1) and severely fragmented (Figure 2). It is highly unlikely that the orchid's pollinators would travel between sites, and consequently the genetic variation within each sub-population is likely to be severely diminished.

Weeds are a threat at Agery, Mona and Muloowurtie. The major weed is Bridal Creeper, and others of concern are Soursobs, Wild Oats and African Boxthorn. Table 2 outlines the weeds present at these sites.

As Table 3 indicates, there is evidence that kangaroos, rabbits or sheep are either present or able to gain access to all five sites monitored in 2001. Table 4 shows that the proportion of flowering Arachnorchis eaten at each site was generally high. (N.B. At Agery, Mona and the Pt Vincent property, flowers of closely related Arachnorchis dilatata complex species were also monitored.) In addition to eating spider-orchid flowers, sheep and rabbits also cause soil erosion and spread weeds.

At Mona and Muloowurtie, trail bikes and 4WD vehicles were creating access tracks, damaging vegetation and causing weed invasion. The situation was exacerbated by illegal firewood cutting and dumping of soil and rubbish. These activities remain a threat to A. macroclavia habitat, although the threat is somewhat diminished since the erection of fencing at both sites.

Clearance has in the past been a threat as well, because it is likely that the species was more common prior to the clearance of bushland for farming, and all known extant sub-populations are now small and isolated. Currently, three of the remaining sub-populations are in small blocks of remnant vegetation on farms, and not protected by any form of conservation management agreement.

Table 2: The weeds present at three A. macroclavia sites. Blank spaces indicate that the weed species is either not present or not considered to be a threat.
Weed Agery Mona Muloowurtie
Bridal Creeper Yes   Yes
Soursobs Yes   Yes
Wild Oats   Yes Yes
African Boxthorn   Yes
Hairy Plantain   Yes  
Exotic grasses Yes Yes  
Exotic herbs   Yes  
Black-berry Nightshade Yes    
Table 3:The herbivores present or believed present at the Arachnorchis macroclavia sites monitored in 2001.
Site Herbivores present
Kangaroos Rabbits Sheep
Agery Reserve Yes Yes  
Mona Reserve Yes Yes  
Muloowurtie Reserve   Yes  
Pt. Julia property     Yes
Pt. Vincent property Yes Yes Yes
Table 4: The number of monitored Arachnorchis flowers eaten, damaged or unfound (possibly eaten) in 2001.
(E = eaten; D = damaged; U = unfound. The term “unfound” refers to plants that were recorded in flower early in the season, but could not be located on subsequent visits.)
Site No. Monitored E D U (E + D + U)%
Agery Reserve 25 7 0 11 72%
Mona Reserve 18 8 0 3 61%
Muloowurtie Reserve 3 1 1 0 67%
Pt. Julia property 1
0
0
0
0%
Pt. Vincent property 47 6 13 6 53%
Total 94 22 14 20 60%