Overview
The Black-mouthed Cup (Plectania melastoma) is a fascinating operculate ascomycete fungus that fruits on mossy decaying twigs in moist coniferous woodlands throughout the temperate Northern Hemisphere. Featuring deep, soot-black, goblet-shaped fruiting bodies accented with tiny reddish-brown granulations along the rim, this quiet decomposer plays a crucial primary role in breaking down woody litter on forest floors.
Biology and Physical Characteristics
The fruiting body (apothecium) of Plectania melastoma is urn-shaped to cup-shaped with a constricted, inrolled margin, supported by a short, stout, root-like stipe buried in the substrate. The interior fertile surface (hymenium) is smooth, shiny, and pitch-black, while the exterior outer surface is dark brownish-black and covered in fine, felty, dark hyphae. Around the mouth of the cup, tiny reddish-orange to rusty granules often appear, giving the species its distinctive scientific name (*melastoma*, meaning ‘black mouth’). Inside the asci, eight smooth, elliptical, hyaline ascospores develop, each containing two small internal oil drops.
Behavior and Ecology
Plectania melastoma fruits in late winter and early spring, capitalizing on cool temperatures and abundant snowmelt moisture. Its subterranean mycelium functions as a specialized saprotroph, decomposing small fallen conifer branches (primarily pines, spruces, and firs) half-buried in damp soil. By digesting stubborn woody fibers and recycling essential carbon, phosphorus, and nitrogen back into forest soils, it facilitates new seedling growth in coniferous ecosystems.
Conservation and Human Impact
Globally evaluated as Least Concern, the black-mouthed cup is widely distributed across undisturbed temperate coniferous woodlands. However, intensive commercial forestry practices—such as clearcutting, heavy machinery soil compaction, and the removal of fallen woody debris—can suppress local mycelial networks. Retaining natural forest deadwood and preserving damp stream corridors supports healthy fungal diversity.
Interesting Factoid
Unlike many cup fungi that emerge in warm summer rain, the black-mouthed cup fruits during early spring thaws, often expanding while partially surrounded by melting ice crystals on the forest floor.
Last updated: October 2026