Conservation and taxonomy of the Caladenia toxochila complex

The species

A group of seven closely related spider orchids that are all pollinated by sexual deception of Thynnid wasps. Species in the complex are distributed throughout the mallee and dry eucalypt woodland regions of South-Eastern Australia.

• Bow-lip Spider Orchid (Caladenia toxochila) – once a widespread species, it is now largely restricted to small, fragmented populations. (FFG Act VIC: CR)

• Coast Spider Orchid (Caladenia conferta) – a Yorke Peninsula endemic, now restricted to two small conservation parks. (EPBC: E)

• Bayonet Spider Orchid (Caladenia gladiolata) – only known from two sites separated by over 250km, with the main population experiencing a major bushfire in 2025 (EPBC: E)

• Eyre Peninsula Spider Orchid (Caladenia hesperia) – only known from a small number of plants across two sites. (requires conservation status assessment) 

• Canberra Spider Orchid (Caladenia actensis) – endemic to the ACT with approximately 250 known plants (EPBC: CR)

• Neat Spider Orchid (Caladenia concinna) – occurs in fragmented populations in central NSW, evidence for multiple cryptic species. (requires conservation status assessment) 

• Charming Spider Orchid (Caladenia amoena) – populations have reduced by 99% in the last ~60 years, leaving just a handful of plants in the wild (EPBC: E, FFG Act: CR)

Why we need to act

Australia’s temperate regions are rich with unique and endemic orchid species. The spider orchids (genus Caladenia) are one of Australia’s largest orchid genera, with well over 300 species. However, Caladenia is also one of the most threatened plant genera in Australia, with approximately one quarter of all described species listed under federal threatened species legislation. The C. toxochila complex is no exception to this trend, with five out of the seven species in the group listed as threatened under federal and/or state legislation.

The taxonomy of the complex remains unresolved, with several described species being difficult to identify based on our current understanding, as well as evidence of unrecognised cryptic species that cannot be conserved until formally described.

Conservation work is dependent on robust taxonomy. Incomplete or inaccurate taxonomy can have detrimental effects when engaging in conservation actions, including inaccurate understanding of species distributions, over or underestimation of population sizes, accidental hybridisation, exclusion of populations and genetic diversity from breeding programs, or translocations of plants into inappropriate areas

Threats to the species

Like many of Australia’s orchids, species in the Caladenia toxochila complex have suffered major declines since European invasion, largely driven by habitat loss and degradation, introduced herbivores, competition by weed species, and loss of pollinators. Climate change is an ever-increasing threat to these orchids, as vital winter rainfall becomes less reliable in semi-arid regions. The combined impacts of these threats have reduced these species to small, highly isolated populations, increasing the risks of inbreeding and local extinctions.

Solution and approach

Resolving the taxonomy of this species complex will facilitate future and ongoing conservation work. To achieve the most accurate taxonomic outcome, this revision will combine multiple lines of evidence:

1. Pollinators – most sexually deceptive orchid species are pollinated by a single insect species, isolating them reproductively from closely related species. Identifying the pollinators of each orchid species provides a solid biological basis for species recognition. Beyond taxonomy, understanding the identity and distribution of pollinators is an important pre-cursor to identifying suitable translocation sites for these orchids.

2. Morphology – fundamentally important to taxonomy and species identification in the field, Andrew will combine traditional (two-dimensional) measurements with novel three-dimensional imaging methods to assess subtle morphological differences.

3. Shade house experiment – by growing each of the species together in a controlled shade house setting, Andrew will be able to separate morphological differences that are influenced by local environmental or seasonal differences, such as soil or rainfall, from those exhibited because of genetic differences. These plants will form the basis of a permanent ex-situ collection that will be available for ongoing conservation work in perpetuity.