Hygrocybe pakelo is a native Hawaiian species, that only grows in native wet-montane forests. The species name ‘pakelo’ refers to the Hawaiian word that means “to slip out of the hand like a slippery fish”. This is indeed a very slippery mushroom, with yellow-golden cap and stem. It is known from only two islands of the Hawaiian archipelago. Native forests are under various threats, development and road construction (especially on Hawai’i), invasion of non-native plants and other organisms, and on Hawai’i where three of the four sites are, the spread of Rapid ʻŌhiʻa Death (Ceratocystis fimbriata), which kills Metrosideros polymorpha the most widespread and dominant native tree of Hawaii. 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 decline in habitat quality.
This species belongs probably in the genus Gliophorus because of the glutinous cap and stem.
Reported from three locations on Hawai’i (two less than 1 km apart), and one from Moloka’i, two islands of the Hawaiian archipelago.
The population is fragmented and consists of small subpopulations on different islands; at present it is known from three locations on Hawai’i, and one on Moloka’i. The habitat where they occur is fragmented as well, due to volcanic activities and the lava streams that surround the tree islands (kipukas) where the species occurs.
Only four subpopulations are known, despite longtime surveys for these conspicuous fungi.
Solitary in mosses over soil or among mosses on fallen hapu’u logs in Montane Mesic Forest (Ohi’a Forest) and Montane Wet Forest (Ohi’a/Hapu’u Forest) (Desjardin & Hemmes 1997). The nutritional mode of Hygrocybe 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.
The populations on Hawai’i (the Big Island) are most threatened.
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; https://cms.ctahr.hawaii.edu/rod/THEDISEASE/DISTRIBUTION.aspx). Ceratocystis fimbriata kills mature trees and since it was first detected in the Kuna and Hilo Districts on the Big Island in Hawaii, it has spread, reached in 2017 the areas where Hygrocybe pakelo 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 islands, as Metrosideros polymorpha is dominant in many different habitats. So far, it is only known to occur on the island of Hawai’i and the situation on the other islands is under constant monitoring.
Secondly, habitat destruction of the kipukas, tree islands in the middle of old lava flows, along the Saddle Road on the Big Island because of widening of the road. The Saddle Road connects Hilo with the observatory on Mauna Kea, and is the shortest route from Hilo to the Kona coast.
Thirdly, the native montane forests of Hawaii are under constant threat of invasive plants and other organisms.
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.
Desjardin, D.E. & D.E. Hemmes, 1997. Agaricales of the Hawaiian Islands. 4: Hygrophoraceae. Mycologia 89: 615–638.
Griffith, G.W., G.L. Easton & A.W. Jones, 2002. Ecology and diversity of waxcap (Hygrocybe spp.) fungi. Botanical Journal of Scotland 54: 7–22.
Halbwachs H., P. Karsch & G.W. Griffith, 2013. The diversity of Hygrocybe – peeking into an enigmatic lifestyle. Mycosphere 4: 773–792. Doi 10.5943/mycosphere/4/4/14
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.