Prasophyllum uvidulum is endemic to northeastern Victoria, Australia, where it is known from a single subpopulation near Shelley in the Upper Murray region. The main factors that make the species eligible for listing in the Critically Endangered category are that it has a very restricted distribution with an area of occupancy (AOO) and extent of occurrence (EOO) of just 4 km²; the species occurs at a single location and is experiencing continuing decline due to threats including feral herbivores, weed invasion, fire regimes that cause declines in biodiversity, localised habitat disturbance and climate change and drought impacts.

Prasophyllum uvidulum is endemic to northeastern Victoria, where it is known from a single population near Shelley in the Upper Murray region. It grows within a small, protected flora reserve, Pheasant Creek Flora Reserve, under the management of Parks Victoria (PV) and the Victorian Department of Energy, Environment and Climate Action (DEECA). The reserve is bounded on all sides by Pinus radiata (Monterey or Radiata Pine) plantations managed by Hancock Victorian Plantation (HVP).

The single known population was burned in the 2019–20 bushfires. Prior to the bushfires, approximately 15 plants were recorded in 2019 and 18 plants in 2018, from DELWP/PV surveys conducted under dry conditions (DELWP and PV 2019). The population has been regularly surveyed over at least 15 years, with approximately 10–25 plants recorded above ground in most years. The maximum number of plants recorded above-ground prior to the 2019–20 fire season was 57 in 2015 (G. Johnson pers. comm. 13 October 2022). All plants surveyed are mature individuals, as only flowering plants were able to be detected, given this is a geophytic species (with underground storage organs) that remains dormant underground for much of the life cycle. Non-flowering plants are difficult to detect amongst other vegetation, particularly when biomass is high (G. Johnson pers. comm. 13 October 2022). The population was previously known from three distinct sites within a small area (approximately 1 km extent), although plants have only been observed at two of the three sites since 2011, with the third site heavily invaded by weeds.

Surveys in 2020 after the bushfires recorded an estimated 300 plants in two closely located groups (G. Johnson pers. comm. 13 October 2022). Post-fire conditions (including substantially reduced vegetation biomass and high rainfall) at the time of survey were close to optimal for flowering, and therefore detection, of this species (M.W .Freestone pers. comm. 21 March 2022). It is likely that most plants in the population would have flowered under these conditions, where only approximately 10% would flower in a given season under average conditions. The large increase in the number of flowering plants in 2020 is not considered to reflect an increase in the population size, but instead reflects that dormant or non-flowering plants were stimulated to flower by the 2019–20 bushfires and subsequent good rainfall, as previously documented in other orchid species (Lamont and Downes 2011, Duncan 2012). In the following year, in 2021, just 30 plants were detected (G. Johnson pers. comm. 13 October 2022) and in 2022 only four flowering plants were recorded (G. Johnson pers. comm. 2 May 2023).

The species has not been found elsewhere despite extensive searches for both plants and similar habitat. There is little similar habitat supporting remnant vegetation in close proximity to the known reserve site, due to the expansive pine plantations in the Shelley area (G. Johnson pers. comm. 13 October 2022). Larger areas of potential habitat in the surrounding area have been converted to pine plantations.

Habitat
Prasophyllum uvidulum lives in winter-wet seepage areas of riparian grassland vegetation, at the margins of a seasonal swamp at approximately 700–750 m altitude. Native grassy woodland occurs around the periphery of this seasonal wetland, within a taller montane eucalypt forest (Jones and Rouse 2009, Duncan and Coates 2010). Plants grow both in areas that are seasonally inundated and in adjacent, slightly higher, grassier areas that are probably not regularly inundated for long periods of time.

Associated native species include Eucalyptus camphora (Mountain Swamp Gum), Acacia melanoxylon (Blackwood), Epacris gunnii (Ace-of-spades Heath), Epacris paludosa (Swamp Heath) and Leptospermum continentale (Prickly Tea Tree) (VBA 2022). Common ground layer species include Baloskion australe (Mountain Cord-rush), Carex appressa (Tall Sedge), Carex gaudichaudiana (Fen Sedge), Machaerina rubiginosa (Soft Twig-sedge) and Restio australis (Mountain Cord-rush) in regularly inundated areas, and Anthosachne scabra (common wheat-grass), Arthropodium milleflorum (pale vanilla-lily), Craspedia variabilis (Variable Billy-buttons), Poa costiniana (Bog Snow-grass) and Rytidosperma penicillatum (Weeping Wallaby-grass) in slightly drier areas (VBA 2022).

Soil at the site is a heavy grey-brown clay loam in the slightly drier parts of the population (Jones and Rouse 2009) and black and peaty in the wetter parts of the population (Jones 2000).

Reproduction and fire ecology 
Prasophyllum species generally take two to five years to reach maturity (primary juvenile period) and can likely live for several decades (TSSC 2006), although a species-specific estimate is unknown. The age of senescence or decline is not well understood but could plausibly be approximately 20–30 years (M.W. Freestone pers. comm. 3 February 2022). 
Prasophyllum uvidulum reproduces via seed, and each plant has a single underground tuber, replaced annually, that allows them to persist underground for long periods. Orchid seeds are generally miniscule in size and therefore wind-dispersed and are not known to form a persistent soil seedbank. While P. uvidulum possess tubers and might therefore be expected to persist in a dormant state during unfavourable conditions, the longer the period without flowering and fresh seed production, the less likely the long-term persistence of a species in an area (Bates 1994).

Prasophyllum uvidulum flowers in December (M.W. Freestone pers. comm. 21 March 2022). Although flowering occurs in the absence of fire, flowering is likely to be stimulated in the year following summer fires, based on the increase in flowering plants following the 2019–20 fire season. Fire is considered likely to occur at low frequency in this community, given the riparian wetland habitat of the species.

Little else is known about the optimal or adverse fire regimes for this species. Periodic fire outside of the growing season is probably beneficial by reducing the amount of competing vegetative biomass of co-occurring species and promoting growth and flowering (Backhouse and Jeanes 1995). Within the non-dormant growing season, fire can be detrimental to the species’ persistence, particularly where fires occur soon after leaf emergence. Tubers at this time may have insufficient resources to sustain a second flush of leaf production, resulting in tuber mortality (Jasinge et al. 2018).

Pollination of P. uvidulum is likely to be unspecialised, as the species likely produces nectar like other leek-orchid species (Backhouse and Jeanes 1995). Likely pollinators include various bees, wasps and flies, although specific information on pollinators of P. uvidulum is lacking. A few Prasophyllum species appear to be primarily self-pollinating (Backhouse and Jeanes 1995). Prasophyllum species, like many orchids, require a fungal symbiont for germination and nutrient uptake (Bates 1994). For P. uvidulum, mycorrhizal fungi found in the roots of adult plants comprise at least two species of Ceratobasidium, at least one of which has been confirmed to support germination (Freestone 2021).

Several threats have been identified as impacting or potentially impacting Prasophyllum uvidulum, particularly grazing by feral animals and weed encroachment on an ongoing basis, as well as fire regimes that cause declines in biodiversity, namely out-of-season fire for this species, with the potential for damaging peat fires. Climate change leading to an increased likelihood of drought and changes to hydrological regimes is also considered a threat. Hydrological changes can also be caused by proximity to pine plantations, potentially as an interacting threat with climate change. Vehicle damage and trampling are also threats. These threats operate across the entire population of this species given its very restricted range.

Prasophyllum uvidulum occurs on the lands of the Jaitmatang people (AIATSIS 2021). The cultural significance of P. uvidulum is currently unknown. Further consultation with the Traditional Custodians of these lands will benefit the conservation of the species by providing awareness of Traditional Knowledge and management practices on Country.

Conservation and management priorities
 
Invasive species impacts (including feral grazing, trampling, predation and weed invasion)

• Continue monitoring and maintenance of the deer fence currently in place around the flora reserve, to ensure exclusion of feral herbivores and two-way access of native herbivores e.g. Swamp Wallaby, Eastern Grey Kangaroo and Wombat that play an important role in ecosystem health via biomass reduction and fungi transfer.
• Continue to evaluate the need for a fence upgrade to ensure effective herbivore exclusion, especially of pigs. Continue the monitoring and weed control programme currently in place by PV and DEECA to prevent encroachment of high threat weeds on the site, particularly from neighbouring pine plantations, using controls not harmful to terrestrial orchids. This will often necessitate weed control by hand.

Fire impacts

• Exclude a seasonal prescribed fire to avoid detrimental effects on P. uvidulum at critical stages of the life cycle, i.e., during the non-dormant phase, from May to early January. While prescribed fire is not used in the surrounding pine plantations, it has been considered for use in the reserve, particularly for control of high biomass of exotic weed species such as sweet vernal grass.
• Ensure rapid response to a seasonal wildfire or peat fires: any future a seasonal wildfire that threaten to burn over recovering sites should be rapidly extinguished, whilst ensuring no new soil disturbance within the reserve. Avoid application of fire retardants in the habitat. Use bio sanitary protocols in accordance with national guidelines (see “Arrive Clean, Leave Clean” Commonwealth 2015) for firefighting machinery.
• Implement experimental ecological burns where monitoring demonstrates a need for this e.g., excessive biomass or abundance of exotic species that are fire intolerant. Fires must be managed to ensure that they support rather than degrade the habitat necessary to the threatened species; that they do not promote invasion of exotic species, and that they do not increase impacts of grazing/predation.
• Fire management authorities and land management agencies should use suitable maps and be aware of field markers in place, to avoid damage to the species.

Climate change impacts

• Investigate options for maintaining in situ persistence as the climate changes, for example by minimising other population pressures, enhancing resilience and promoting recruitment or supplementing existing population. Breeding, seed collection, propagation and other ex situ recovery action
• Continue to collect and store seed and mycorrhizal fungi using suitable protocols (Martyn Yenson et al. 2021).
• Cultivate additional ex situ collections of P. uvidulum to safeguard against the unforeseen destruction of the wild population. A very small number of P. uvidulum plants, as well as fungal symbionts, are already in cultivation in the Royal Botanic Gardens Victoria collection (M.W. Freestone pers. comm. 3 February 2022), therefore ex situ propagation methods and nursery cultivation requirements are now reasonably well known.
• Establish new translocated populations and bolster the existing population with cultivated plants to improve the conservation outlook of the species in areas of suitable habitat. To achieve this, additional seed collections and site selection with suitable habitat is required. The Royal Botanic Gardens Victoria have some seed and mycorrhizal fungi in storage and have established successful germination protocols for P. uvidulum with seedlings germinated in March 2023 (germination methods from Freestone et al. 2022; N. Reiter pers. comm. 17 April 2023). New populations should be established implementing national translocation protocols (Commander et al. 2018).
•  Monitor all translocated individuals to maturity, seed set and recruitment to ensure they are viable and are contributing to a reduction in the extinction risk for the species. 

Recreation impacts

• Ensure unauthorised vehicle access is minimised – currently the deer fence minimises access. 

Stakeholder engagement/community engagement

• Continue work between DEECA, PV and neighbouring pine plantation owners Hancock Victorian Plantations (HVP) to manage threats in surrounding areas that are likely to impact the population, particularly weeds and feral herbivores.
• Identify opportunities for, and promote and support, the continued involvement of community groups and volunteers in recovery activities for the species, particularly Koetong Landcare group and the Upper Murray Landcare Network.
• Update available information about the species, including information about its appearance, habitat, threats, recovery actions and the importance of locating, monitoring and protecting populations over the long-term.
• Relevant Traditional Custodians should be identified and consulted with on all planned recovery actions. Effort should be made to collaborate with Traditional Custodian groups in the implementation of any actions.
• Engage cultural knowledge custodians and land rights holders in conservation actions, including the implementation of Indigenous fire management and other survey, monitoring and management actions. Enable the sharing of knowledge, while ensuring the processes and protocols to record, store, and share any knowledge are agreed and appropriately resourced. Information on the application of cultural burning and integrated Caring for Country practices to protect and enhance habitat is of critical importance.

Survey and monitoring priorities

• Continue the current DEECA/PV demographic monitoring programme and implement further monitoring to determine:

1.  trends in population size and stability, potential habitat and habitat condition/ degradation
2. levels of seed production and recruitment
3. success of in situ and ex situ population enhancement measures.

• Survey and map actual and potential habitat, using ecological and bioclimatic information that may indicate habitat preference.
• Identify possible reintroduction sites and determine the suitability of surveyed habitat for conservation translocations of the species. 

Information and research priorities

• Conduct research into the life history and ecology of the species, given the paucity of available information. This includes determining plant longevity, phenology and seasonal growth rates, pollinator biology and requirements, recruitment and mycorrhizal symbionts. Additional research priorities could include minimum viable population size, the role of seed predators and other disturbances on recruitment via seed, roles of competition and rainfall in recruitment, and reproductive strategies.
• Conduct research into the effect of different fire regimes, both by monitoring the population at different stages in the fire cycle, as well as by experimentation on related, but less threatened Prasophyllum species. This would allow inference about the effects of frequency, severity and seasonality of fire on survival and recruitment. Both seasonality (Jasinge et al. 2018) and fire frequency (Coates et al. 2006) are known to affect population persistence in other orchid species. It may be difficult to replicate conditions from the 2019–20 fire season in-situ, as this season was exceptionally dry and hot.
• Research the factors influencing the effectiveness of conservation translocations for this species.
• Research appropriate controls for sweet vernal grass, which is difficult to control due to the presence of native species amongst this weed (G. Johnson pers. comm. 13 October 2022). Controlled burning at appropriate times may be an option for control of this weed species.
• Understand the impact of adjoining pine plantations and their management on the hydrology of P. uvidulum population.
• If feasible, undertake vulnerability assessments of the species’ sensitivity and adaptive capacity to changing climatic conditions which draw on genetic, physiological or ecological evidence.
• If vulnerability assessments indicate the species has a high likelihood of extinction due to climate change, undertake research to identify climate refuges that may be suitable for translocations, including both modelling and experimental approaches (e.g. trial translocations). Consideration should be given to the benefits to the species in mitigating climate change related threats, as well as the risks to the recipient site (e.g. introduction of diseases, pests and/or pathogens, and invasiveness of the species).