White green-algae coral

In the thallus of M. mucida, the algae are not merely scattered. Instead, they are organised into small, closely situated globules embedded in a gelatinous matrix on moist, rotting wood. This Botrydina-type thallus structure, common in basidiolichens, serves multiple functions. It protects the algae from UV light and desiccation, while ensuring close contact through a hyphal network that provides a continuous water and minerals supply. The fruiting bodies (basidiocarps) are typically simple to lobed and can reach up to 2 cm (0.8 in) in height. They are waxy-tough but can become slimy, transitioning from white or creamy colour to grey or pale tan as they mature. These structures often dry to show a pure white tip. The fruiting bodies' stickiness often causes debris to adhere to their surfaces. The algal partners are encapsulated in tiny pockets of fungal tissue, yet they retain a loose, unstructured form, manifesting as a green granular crust where the fungus produces its fruiting bodies. Despite their mutualistic relationship, both the algae and the fungus maintain their individual morphology. The relationship between coccomyxoid green algae and M. mucida was documented by Geitler in 1955, noting that the algae are larger within the lichen than when free-living. …

This species is commonly found on decomposing wood, often in the presence of algae. It thrives on a wide variety of substrates, including bamboo, beech, cedar, poplar, and oak. In Central Europe, coniferous wood is a particularly favoured substrate. M. mucida is widely distributed, found in Asia, Europe, North and South America, and possibly Australia, with its North American range extending as far north as Alaska. The discovery of M. mucida at unusually low elevations, specifically around 130 to 135 m (427 to 443 ft) above sea level in the Bienwald area of Rhineland-Palatinate, has prompted a reevaluation of its distribution and naming inconsistencies across different scientific literatures. Unlike other members of its genus, which prefer sandy soils, this species predominantly relies on rotting wood in moist environments. Lothar Geitler first identified this species as an extratropical lichen in 1955, challenging the then-prevailing view that basidiolichens were exclusively tropical. Previously considered native to Northern Europe and the mountains of Central Europe, M. mucida has been increasingly observed across most European countries and globally. This expansion in its geographical range could be attributed to the establishment and maintenance of natural forest reserves, environments that foster the decay of thick logs and provide suitable habitats for the fungus. …

The species epithet mucida is from the Latin word mucidum, meaning "mouldy" or "slimy"; the genus name Multiclavula means "many clubs". In North American literature, this fungus is known by several vernacular names, including "scum lover", "common club mushroom lichen", "frail bones", and "club lichen", the last of which is also used to refer to the entire genus.