Marasmius thiersii was described from collections made in the Sierra Nevada Foothills, in California, USA (Desjardin 1987).

Recent genetic work has led to reclassification of many Marasmius (Oliveira et al. 2019); yet nothing specific has been published on M. thiersii.

A number of similar species might be mistaken for M. thiersii, including a few which remain undescribed.

Marasmius thiersii is a small mushroom with a dark reddish brown to dark brown cap, grayish buff gills, a pruinose to finely velvety stipe, a slight odor and strong alliaceous taste (similar to garlic or onions).

Rare; currently known from nine collections from four locations; three in the north-central Sierra Nevada Foothills, and one on California’s north coast.

Presumed suitable habitat is widespread and stable.

Currently known from three locations in the Sierra Nevada foothills of California, USA, and one location on the north coast in Mendocino County, CA.

Rare; currently known from nine collections from four locations; three in the north-central Sierra Nevada Foothills, and one on California’s north coast.

Being a poorly known species, more collections are needed, and additional habitat information should be carefully recorded in order for an assessment to be made. Some of the apparent rarity is likely due to difficulties in finding this species, and identifying it as such.

Apparently appropriate substrates for this species are found over huge areas of the Sierra Nevada, Cascade Range, and coastal forests.  The gregarious fruiting habits likely enable plentiful spore production. However, rarity of this species may be partially explained if such fruitings are infrequent, the spores have low viability, and/or if our understanding of appropriate habitats lacks important factors.

Saprobic. Scattered to gregarious on duff, leaves and needles, fruiting in fall and early winter. Primarily on needle litter of pines (Pinus spp.), but occasionally on Tanoak (Notholithocarpus densiflorus), Madrone (Arbutus menziesii) or manzanita (Arctostaphylos spp.) leaves.

No specific threats have been identified with regards to this species. Portions of the habitat are more susceptible to stand replacing forest fires, but if this is detrimental to the population in the long term remains unknown.

Until more is known about habitat requirements of this species, no specific conservation actions can be recommended with regards to this species.

Targeted surveys by individuals able to distinguish this species from its look-alikes are needed, as well as regular monitoring at known localities to determine typical periodicity of fruitings. If more locations are discovered, detailed habitat notes should be made.

None known.

Desjardin, D.E. 1987. New and noteworthy marasmioid fungi from California. Mycologia 79: 123–134.

Desjardin, D.E. 1987. The Agaricales (Gilled Fungi) of California 7. Tricholomataceae I. Marasmioid Fungi: The Genera Baeospora, Crinipellis, Marasmiellus, Marasmius, Micromphale, and Strobilurus. Mad River Press, Eureka, CA.

Desjardin, D.E., Wood, M.G. and Stevens, F.A. 2015. California Mushrooms: The Comprehensive Identification Guide. Timber Press, Portland, OR.

MyCoPortal. 2021. http://mycoportal.org/portal/index.php. Accessed on February 22.

Oliveira, J.J.S., Vargas-Isla, R., Cabral, T.S., Rodrigues, D.P. and Ishikawa, N.K. 2019. Progress on the phylogeny of the Omphalotaceae: Gymnopus s. str., Marasmiellus s. str., Paragymnopus gen. nov. and Pusillomyces gen. nov. Mycological Progress 18(5): 713-739.

Siegel, N., Vellinga, E.C., Schwarz, C., Castellano, M.A. and Ikeda, D. 2019. A Field Guide to the Rare Fungi of California’s National Forests. Bookmobile: Minneapolis, MN. 313 p.