Humidicutis peleae is a native species of the native wet-montane forests of Hawaii, occurring on several islands. Its occurrence in Hawai’i is threatened by the extirpation of the overstory tree in its habitat (viz. Metrosideros polymorpha, killed by Ceratocystis fimbriata), road construction, and in general the invasion of non-native plants and other organisms. The reasons to list this species as Vulnerable under criterion A3(e) is that more than half of the known locations are on Hawai’i, in the zone where Ceratocystis fimbriata occurs. Ceratocystis kills the overstory tree, Metrosideros polymorpha, on which Humidicutis relies for its habitat. Indirectly it is the effect of an introduced parasite of the tree. The life span of three generations is estimated to be 30 years.
Known from isolated locations on four islands of the Hawaiian archipelago, viz. Hawai’i, Kaua’i, Maui, and Moloka’i.
Currently known from collections made at 11 different locations, on four different islands, one on Kaua’i, two on Moloka’i, one on Mau’i, and seven on Hawai’i. Unknown from Oahu. Six of the seven Hawai’i collections were made in isolated patches of native forest along the Saddle Road.
Solitary to scattered, on bryophyte-covered soil or among bryophytes on rotten logs of ohi’a (Metrosideros polymorpha) or stems of hapu’u (Cibotium spp.) in Montane Wet Forest (Ohi’a/Hapu’u Forest) or Montane Mesic Forest (Ohi’a Forest), in one locality in duff under Monterey Cypress (Cupressus macrocarpa) adjacent to Montane Wet Forest (Desjardin & Hemmes 1997).
Nutritional mode not known, presumably 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 the Big Island in Hawai’i, it has spread, and reached in 2016 the area where Humidicutis peleae occurs on Hawai’i, 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). As of 2017, the disease has only been found on Hawai’i, but it is feared that it will move to the other islands. The seven known locations for this species are all in the area where the disease has been found.
Secondly, habitat destruction by widening the Saddle Road on Hawai’i [the Big Island] along which this species occurs. So far, the kipukas (tree islands among old lava streams) where this species is found have been spared.
And thirdly, invasion of non-native plants and other organisms is a constant threat for all native forests of the Hawaiian islands.
Some sanitary actions to restrict the spread of Ceratocystis fimbriata are already in place to prevent the species from spreading within Hawaii and to the other islands, but the spread on Hawai’i has not been stopped yet.
Road widening has to be restricted and been executed in such a way that the kipukas where this species occurs are left in tact.
Several locations are in protected areas and forest preserves.
Desjardin, D.E. & D.E. Hemmes, 1997. Agaricales of the Hawaiian Islands. 4: Hygrophoraceae. Mycologia 89: 615–638.
Keith, L.M., R.F. Hughes, L.S. Sugiyama, W. P. Heller, B.C. Bushe & J.B. Friday. 2015. First Report of Ceratocystis wilt on ʻŌhiʻa. Plant Disease 99: 1276. http://dx.doi.org/10.1094/PDIS-12-14-1293-PDN
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.
Mycology Collections Portal http://www.mycoportal.org [accessed Feb 2018]