Humidicutis poilena is a very rare species, that is, despite surveys in suitable habitat, not known from more than one locality on the island Hawai’i, in wet-montane forests, dominated by Metrosideros polymorpha. The habitat is under severe threat by the rapid spread of an introduced pathogen of Metrosideros polymorpha, Ceratocystis fimbriata, that kills the trees. Other threats to the habitat is destruction by road construction, and introduced other organisms such as non-native plants. A reduction in population size of more than 30% is projected within the span of 3 generations (30 years) for this species, due to the spread of an introduced pathogen that kills the overstory tree, Metrosideros polymorpha, which results in a severe decline in habitat quality. The species has been found in one locality, but the habitat is more widespread, but despite surveys in the past 25 years, has not been found.

Humidicutis poilena is a very rare species, that is, despite surveys in suitable habitat, not known from more than one locality on the island Hawai’i, in wet-montane forests, dominated by Metrosideros polymorpha. The habitat is under severe threat by the rapid spread of an introduced pathogen of Metrosideros polymorpha, Ceratocystis fimbriata, that kills the trees. Other threats to the habitat is destruction by road construction, and introduced other organisms such as non-native plants.

Known from one locality along the Saddle Road on Hawai’i, one of the islands of the Hawaiian archipelago, Hawaii, U.S.A.

Known only from one population on Hawai’i, where it was found twice in 1995. Despite ongoing survey efforts, it has not been found since.

Solitary to scattered among mosses on fallen hapu’u logs (Cibotium spp.) in Montane Mesic Forest (Ohi’a/Hapu’u Forest) (Desjardin & Hemmes 1997).
Nutritional mode not known, assumed to be biotrophic, but not ectomycorrhizal (Seitzmann et al. 2011).
Dispersal by wind-borne spores.

Habitat destruction is the biggest threat to the occurrence of this species, first of all because of a rapidly spreading deadly disease of the overstory tree (Metrosideros polymorpha; ʻŌhiʻa), caused by Ceratocystis fimbriata (Keith et al. 2015; ). Ceratocystis fimbriata kills mature trees and since it was first detected in the Kuna and Hilo Districts on Hawai’i [the Big Island], it has spread, and reached in 2016 the area where Humidicutis poilena occurs, and is threatening all habitats in which Metrosideros is the dominant tree. The name of the disease, Rapid ʻŌhiʻa Death, is an indication of its sudden appearance and fast work. This will change the whole ecosystem of the island, as Metrosideros polymorpha is dominant in many different habitats (https://cms.ctahr.hawaii.edu/rod/THEDISEASE/DISTRIBUTION.aspx).
Secondly, habitat destruction by widening the Saddle Road along which this species occurs. So far, the kipuka (tree island among old lava streams) where this species is found has been spared.
And thirdly, invasion of non-native organisms is a constant threat for all native forests of the Hawaiian islands.

Sanitary actions to restrict the spread of Ceratocystis fimbriata have to be taken immediately, and action to maintain the kipukas along the Saddle Road on the Big Island are needed.
Raising awareness about the mycological value of the kipukas on Hawai’i is also necessary.

Desjardin, D.E. & D.E. Hemmes, 1997. Agaricales of the Hawaiian Islands. 4: Hygrophoraceae. Mycologia 89: 615–638.
Seitzman, B.H., Ouimette, A., Mixon, R.L., Hobbie, E.A. & Hibbett, D.S. 2011 – Conservation of biotrophy in Hygrophoraceae inferred from combined stable isotope and phylogenetic analyses. Mycologia 103: 280–290.

https://cms.ctahr.hawaii.edu/rod/THEDISEASE/DISTRIBUTION.aspx