Small agaric, growing on an algal mat on litter or wood, with a white spore print. Pileus pale or pinkish, not viscid. Lamellae adnexed or adnate. Stipe excentric or lateral. Partial veil remnants absent. Odour very strong, disagreeable. Spores hyaline, non-amyloid, smooth; germ pore absent. Cheilocystidia present. Pileipellis a cutis or a trichoderm. Clamp connections present.

The growth on an algal mat and the strong odour make this a very distinctive agaric. The only other lichenised agarics are in Lichenomphalia, which has fruit-bodies growing on the ground with a central stipe and decurrent lamellae. Apart from the lichenisation, some species of Gymnopus (which in FunKey includes the other species of Marasmiellus) are very similar. Other white to pale, small, white-spored agarics growing on wood with the stipe lateral or absent include Campanella (with widely-spaced lamellae that have interconnections), Chaetocalathus (pileus hairy), Cheimonophyllum (pileus pure white) and Tetrapyrgos olivaceonigra (lamellae with interconnections and spores nodulose or triangular).

Marasmiellus Murrill, N. Amer. Fl. 9: 243 (1915).

One species: Marasmiellus affixus.

Marasmiellus affixus (Berk.) Singer, Beih. Nova Hedwigia 44: 4 (1973).

S.A., N.S.W., Vic. and Tas.

In native forests.

On wood, or woody debris. Often in large numbers, with obvious bleaching of the substrate associated with the colony of fruit-bodies. Grows on an algal mat.

Saprotrophic. This fungus is considered to be lichenised.

Fuhrer, B. (2005), A Field Guide to Australian Fungi. Bloomings Books, Hawthorn. [Description and Illustration of M. affixus]

Fuhrer, B. & Robinson, R. (1992), Rainforest Fungi of Tasmania and South-east Australia. CSIRO Press, East Melbourne. [Illustration of M. affixus]

Kantvilas, G. & May, T.W. (1995), Additional lichen records from Australia. 26. Marasmiellus affixus (Berk.) Singer, an overlooked basidiolichen, Australas. Lichenol. Newslett. 37: 32–34. [Brief notes on M. affixus]

McCann, I.R. (2003), Australian Fungi Illustrated. Macdown Productions, Vermont. [Illustration of M. affixus]

Singer, R. (1973), The genera Marasmiellus, Crepidotus and Simocybe in the Neotropics, Beih. Nova Hedwigia 44: 1–517. [Microcharacters of M. affixus and discussion of lichenisation]

Singer, R. (1975), The neotropical species of Campanella and Aphyllotus with notes on some species of Marasmiellus, Nova Hedwiga 26: 847–895. [Microcharacters of M. affixus and discussion of lichenisation]