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Societal Impact Statement: Conservation seed banks maintain collections of many seed‐bearing plant species, providing germplasm and data to support management of wild populations. However, a proportion of plant species produce seeds that are difficult to collect, dry, store and utilise; these are known as 'exceptional' species. Here we tested a framework for identifying exceptional species, to document examples and provide case studies within the Australian flora. We present a workflow that may be used to identify additional exceptional species, and direct efforts to establish appropriate collection types (seeds and/or living collections, tissue culture or cryopreservation) for their ex situ conservation. Summary: Seed banking is well established to contribute to the conservation of many seed‐bearing plant species ex situ for future use in restoration, translocation, agriculture and horticulture. In Australia, over 67% of currently listed threatened plants are represented in conservation seed banks. However, there are challenges to conserving the full extent of plant diversity in seed banks, with growing recognition that we need to think beyond conventional seed banking methods to conserve 'exceptional' plant species that are difficult to collect, store and germinate. We examine how the framework for identification of such species can be applied to the Australian flora, using examples from the recently published guidelines for 'Plant Germplasm Conservation in Australia' and case studies and data arising from the Australian Academy of Science Fenner Conference on the Environment 'Exceptional Times, Exceptional Plants'. We present a workflow to assist conservation decision‐makers and practitioners in identifying exceptional species and overcoming barriers to storage of germplasm, enabling appropriate ex situ collection types to be established via seeds, living collections, tissue culture, cryopreservation or a combination of these. Australia's seed conservation sector continues to expand, with increasing expertise, facilities and networks established to conserve a diversity of plant species; however, resolving the challenges relating to each exceptionality factor requires significantly more time, labour and collaboration than current capacity allows. Understanding the barriers to conservation and production of healthy plants, via germination or other methods of propagation, is a critical component of conserving species long‐term and ultimately returning plants to the landscape. [ABSTRACT FROM AUTHOR]

Specialized mycorrhizal interactions have the potential to limit the geographical range of plant species and contribute to reproductive isolation. We investigated these predictions in Caladenia (Orchidaceae) from south-western Australia, a group known to have specialized mycorrhizal associations with the genus Sebacina s.l. Sequencing of fungal isolates from 47 of the 136 species of Western Australian Caladenia was undertaken to resolve the geographical range and habitat preferences of mycorrhizal fungal operational taxonomic units (OTUs) and their host breadth in Caladenia. Eight different fungal OTUs were used by Caladenia, with the more frequently detected OTUs occurring in a wide range of habitats and geographical regions. Given the comparatively narrow geographical ranges of most Western Australian Caladenia taxa, this suggests that the geographical ranges of fungal OTUs are unlikely to limit the geographical range of Caladenia spp. Extensive sharing of fungal OTUs between closely related orchid species was detected, suggesting that in the main there is little potential for mycorrhizal fungi to contribute to reproductive isolation between Caladenia spp. Our data mostly support previous work suggesting high mycorrhizal specificity in Caladenia, but this may not be the case in all subgenera, highlighting that Caladenia may offer powerful opportunities for investigating the evolution of specialized mycorrhizal associations. [ABSTRACT FROM AUTHOR]

Myrtle rust is a plant disease caused through infection by the fungus Austropuccinia psidii and was first detected in Australia in 2010. The disease has spread through New South Wales, Victoria, Queensland, the Northern Territory, and Tasmania. In this short timeframe, myrtle rust has had a devastating impact on many native species in the family Myrtaceae, including several rainforest species that are now at risk of extinction. In 2022, myrtle rust was first detected in the northern part of Western Australia (WA)-the largest state in Australia. WA is home to ca. 2000 Myrtaceae taxa ( ca. 60% of Australia's Myrtaceae diversity), many of which form the dominant component of the vegetation across several ecosystems (e.g., Eucalyptus, Corymbia, Melaleuca, Agonis, Verticordia etc.). While modelling suggests that the environmental conditions in WA's north are less conducive to myrtle rust in comparison to the wet, temperate rainforests of the east coast, WA's temperate, Myrtaceae-rich south coast may be climatically suitable. Coupled with the sheer abundance of Myrtaceae species in WA, their high degree of endemism, high proportion of threatened species, and little available information on their susceptibility to myrtle rust, a pre-emptive strategy to conserve germplasm of at-risk species is warranted. This paper highlights the role of ex situ germplasm conservation in responding to biosecurity threats such as myrtle rust. With early intervention critical to sourcing healthy and genetically diverse germplasm, we present a prioritized list of genera and species of Myrtaceae in WA to inform strategic, coordinated, and timely ex situ conservation actions, along with case studies to illustrate the complementary approaches of seed banking, cryobiotechnology, and tissue culture necessary to conserve germplasm of WA's myrtaceous flora.