Kingdom: Fungi; Phylum: Basidiomycota; Class: Agaricomycetes; Order: Agaricales; Family: Marasmiaceae; Genus: Rhodocollybia
Description and Significance
Young pileus is bell-shaped, 30-80 mm in diameter, and enlarges to a wide convex knob-like structure as it ages. The underside of the pileus reveals narrow lamellae, which form maze-like patterns near the stipe. The stem is 5-20 mm in diameter and emerges from branched rhizomorphs. The pileus has a flat underside and convex upper side, with a slightly elevated umbo. The outer border of the umbo typically has a shallow depression, with the edges occasionally undulated and raised upward as the fungus ages. The surface of the pileus is slippery and can appear smooth or creased. Reddish brown spots cover the surface of the pileus, which also displays light brown to light orange splotches in the young fungus that fade over time . R. laulaha occupies elevational gradients within the montane and mesic rain forests of Hawai'i. It spans a geographic range encompassing the mountainous slopes of the three Hawaiian Islands: Kaua'i, Maui, and Hawai'i Island, and is also found in the Neotropics. The basidiocarp are commonly seen in leaf litter, porous volcanic rock, or rotten logs, either growing in clusters or solitarily. Rhodocollybia laulaha was the first fungal species in Hawai'i utilized to study the population genetics of fungi . The species serves as a useful model for studying divergence and gene flow patterns in fungal populations due to the presence of geographically isolated populations that occupy varied ecological habitats across the Hawaiian archipelago. Still, little is known about the evolution of native fungal species in the Hawaiian Islands .
Life Cycle, Cell Structure, Metabolism
Basidiome production occurs readily in July through December, and are rarely seen during other times of the year, despite optimal conditions . Club-shaped basidia contain four basidiospores that are dispersed by forcible discharge . Several unique morphological features characterize the basidiospores: the ellipsoid shape; complexity of the outer hyphal layer; and the twisted shapes of the caulocystida cells within the basidiocarp stalk . Evidence has shown that the spores of ectomycorrhizal fungi rarely disperse farther than 100 m, implying that it is unlikely that the spores of R. laulaha dispersed between the Hawaiian Islands . The rhizomorphs consist of interwoven cylindrical hyphae by which the fungi reproduce asexually, and may enable the fungus to persist in a site for many years .
The G28 microsatellite locus was developed from R. laulaha and has been utilized in studies to examine the evolution of microsatellites in fungi because it contains a tri-nucleotide sequence motif . G28 in R. laulaha was found to contain seven alleles that are present within several populations . Two alleles from the G28 locus were found in populations growing on Kaua'i, Maui, and Hawai'i Island. Kierle et al. (2011) found private microsatellite alleles in a Kaua'i population and separate private alleles in two populations on Hawai'i Island, which were alleles not found to exist in any other R. laulaha populations. Interestingly, genotyping of individual populations of R. laulaha on different logs showed that each log population contained a clonal colony of genetically similar individuals .
Ecology and Pathogenesis
R. laulaha is a saprobic fungi that often associates with native plants of Hawai'i, including 'Ohi'a (Metrosideros polymorpha), Koa (Acacia Koa), and Hapu'u Fern (Cibotium menziesii) . The fungi play an important role in the decomposition of these endemic species by feeding off the organic compounds on the forest floor . As a saprotrophic fungus, it does not form a parasitic symbiosis with living plant tissue. The mushroom is edible with reports of having an unpleasant and bitter taste . Populations show recent fragmentation within subdivided native forests that have experienced deforestation. Lack of genetic equilibrium and shared alleles observed between geographically distinct populations is attributed to recent colonization events and habitat loss .
 Desjardin, D. E., Halling, R. E., & Hemmes, D. E. Agaricales of the Hawaiian Islands . 5 . The Genera Rhodocollybia and Gymnopus. (1998). Mycologia, 91, 166 - 176. doi: https://www.jstor.org/stable/3761206
 Keirle, M. R., Avis, P. G., Feldheim, K. A., Hemmes, D. E., & Mueller, G. M. (2011). Investigating the Allelic Evolution of an Imperfect Microsatellite Locus in the Hawaiian Mushroom Rhodocollybia laulaha. Journal of Heredity, 102(6), 727-734. doi: http://dx.doi.org/10.5061/dryad.jm65k
 Keirle, M. R., Avis, P. G., Hemmes, D. E., & Mueller, G. M. (2010). Variability in the IGS1 region of Rhodocollybia laulaha: is it allelic, genomic, or artificial?. Fungal Biology, 115, 310-316. doi: 10.1016/j.funbio.2011.01.002
 Keirle, M. R., Avis, P. G., Hemmes, D. E., & Mueller, G. M. (2012). Limited divergence in the spatially subdivided population of the Hawaiian mushroom Rhodocollybia laulaha. Botany, 90, 1103-1112. doi: 10.1139/b2012-082
 Keirle, M. R., Avis, P. G., Hemmes, D. E., & Mueller, G. M. (2014). Testing the "one-log-one-genet" hypothesis: methodological challenges of population sampling for the Hawaiian wood-decay fungus Rhodocollybia laulaha. Mycology, 106(5), 896-903. doi: 10.3852/13-079
Page authored by Alexandra Pond, student of Dr. Marc Orbach, University of Arizona .