Solioccasus polychromus is a hypogeous species, known from tropical and subtropical forests in Australia and Papua New Guinea. It was only described in 2013 and is likley undersampled due to its inconspicuous fruitbodies. Nevertheless, it is already known from approximately 20 sites, and population size is estimated at 100000 mature individuals, with no evidence of significant population decline. Therefore, this species is assessed as Least Concern (LC).
Type and only species in the Solioccasus genus, established in 2013 based on morphological and phylogenetic evidence (Trappe et al., 2013). It has no synonyms.
Found in Papua New Guinea (Western Province) and in lowland tropical and subtropical forests in Australia, in the states of Northern Territory (Arnhem Land) and along the coast and coastal mountains of Queensland (Cape York to Brisbane). (Trappe et al., 2013)
Known from roughly 20 sites (5 in Papua New Guinea, 15 in Australia) (Trappe et al., 2013; GBIF.org, 2023), though it is difficult to determine the exact number from location descriptions. Observations and known sites are likely limited by its inconspicuous fruitbodies, which despite being brightly coloured are mostly hypogeous, small, and sometimes covered by forest litter. Taking this into account, as well as the recent description of the species, and large number of potential hosts, a large multiplier for unknown sites can be applied (e.g. x500). Following guidelines by Dahlberg and Mueller (2011) population size is therefore projected to be above 100000 mature individuals, assuming 10 mature individuals exist per site.
It is possible there is some small decrease in population size due to habitat decline, but this is difficult to establish. Estimates by Global Forest Watch (2023) show a decrease of 4.2% of tree cover (>30% canopy density) in the area of distribution of this species for a period of 20 years from 2001 and 2021. Nevertheless, assuming a linear decline, a decrease in population size through habitat loss is not projected to meet criteria for threatened categories in a 50 year period.
Population Trend: Uncertain
Given its phylogenetic placement S. polychromus is assumed to be ectomycorrhizal but no host has been confirmed. Nevertheless, it is found in lowland tropical and subtropical forests, dominated by or in a mixture of ectomycorrhizal trees which constitute potential hosts, such as Allocasuarina littoralis, Corymbia spp. (C. dichromophloia, C. erythrophloia, C. polycarpa), Eucalyptus spp. (E. pellita, E. pilularis, E. racemosa, E. tetrodonta), Leptospermum spp., Lophostemon sp. and Melaleuca spp..
The fruitbodies are hypogeous or partly emergent, gregarious, and grown in sand or soil, often covered by forest litter. Spore dispersal is thought to occur through mycophagist species, namely by mammals and birds between Papua New Guinea and Australia through the Torres Strait.
Species may be threatened by changes in habitat quality within its distribution, namely in Queensland’s Tropical Rain forests region. This includes disturbances caused by habitat fragmentation caused by roads and powerline construction, presence of invasive species such as Phytophthora cinnamomi, tourism within protected areas, pollution from agricultural runoff, changes in fire regime and climate change (Williams et al. 2011 and Stork et al. 2011)
Research into the ecology of the species is needed to help establish potential threats, determine host preference and species.
No known anthropogenic uses
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