Assessment Notes

Justification

Hygrocybe lamalama is a conspicuous deep orange to yellow-orange species with a dry cap and stem, which is found only in native tropical wet montane forests dominated by Metrosideros polymorpha (ʻŌhiʻa) and Cibotium spp. on four Hawaiian islands. The habitat is under constant threat, from invasion of non-native plant species, habitat destruction for road construction (especially on Hawai’i), and lately especially the rapid spread of ʻŌhiʻa rapid wilt, caused by Ceratocystis fimbriata which kills ʻŌhiʻa trees. A reduction in population size of more than 30% is projected within the span of 3 generations (30 years) for the occurrence of this species on Hawai’i, due to the spread of the introduced pathogen that kills the overstory tree, M. polymorpha, which results in a severe decline in habitat quality, making it unsuitable for this species. The main subpopulation of this species is known from Hawai’i with fewer records from Kaua’i, Mau’i, and Moloka’i, where the habitat is still widely available. Therefore, Hgrocybe lamalama is listed as Vulnerable under criteria A3ce+4ce.

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Geographic range

This species is endemic to Hawaii, U.S.A. It is known from a few sites on four Hawaiian islands: Hawai’i, Kaua’i, Maui and Moloka’i.

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Population and Trends

Hygrocybe lamalama grows only in native tropical wet montane forests dominated by Metrosideros polymorpha (ʻŌhiʻa) and Cibotium spp. The habitat is under constant threat, from invasion of non-native plant species, habitat destruction for road construction (especially on Hawai’i), and, lately, especially the rapid spread of ʻŌhiʻa rapid wilt, caused by Ceratocystis fimbriata which kills ʻŌhiʻa trees. A reduction in population size of more than 30% is projected within the span of 3 generations (30 years cf Dahlberg and Mueller 2011) for the occurrence of this species on Hawai’i, due to the spread of the introduced pathogen that kills the overstory tree, Metrosideros polymorpha, which results in a severe decline in habitat quality, making it unsuitable for this species. The main subpopulation of this species is known from Hawai’i with fewer records from Kaua’i, Mau’i, and Moloka’i, where the habitat is still widely available.

Population Trend: Decreasing

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Habitat and Ecology

This species is solitary to scattered, seldom gregarious, in soil or among mosses (mainly Rhizogonium sp.) in Montane Mesic Forest (Ohi’a Forest) and Montane Wet Forest (Ohi’a Forest), or seldom in Montane Mesic Forest dominated by koa (Acacia koa) (Desjardin and Hemmes 1997). The nutritional mode of Hygrocybe and Gliophorus species is still not fully understood; it is presumably biotrophic, but how is not clear yet. Hygrocybe is not saprotrophic, nor ectomycorrhizal (Griffith et al. 2002, Halbwachs et al. 2013, Seitzmann et al. 2011). Dispersal is by airborne spores.

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Threats

The major threats to the habitat in which this species grows are: habitat destruction because of road construction (in particular widening of the Saddle Road on Hawaii - so far the tree islands among the lava streams (kipukas) where the species is found have been spared). Additionally, the species may be impacted by habitat destruction because of a rapidly spreading deadly disease of the dominant tree (Metrosideros polymorpha; ʻŌhiʻa), caused by Ceratocystis fimbriata (Keith et al. 2015; see also College of Tropical Agriculture and Human Resources, University of Hawai'i at Manoa 2019). The disease had been found on Hawaii only, but occurrences have now been reported from other islands (see College of Tropical Agriculture and Human Resources, University of Hawai'i at Manoa 2019). Lastly, invasion of other non-native species is an ever present threat to native forests on these isolated islands.

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Conservation Actions

Sanitary actions to restrict the spread of Ceratocystis fimbriata have to be taken immediately, to prevent the spread into more montane habitats. Raising awareness of the mycological importance of the tree islands (kipukas) on Hawaii is also necessary.

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Source and Citation

Vellinga, E.C. 2019. Hygrocybe lamalama. The IUCN Red List of Threatened Species 2019: e.T125434891A125435610. Accessed on 22 November 2025.

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• Country occurrence