Overview
The Black Felt Cup (Plectania nannfeldtii), also known in field mycology as the snowbank black cup, is an intriguing ascomycete fungus exquisitely adapted to high-altitude montane and subalpine environments in western North America. Fruiting almost exclusively in the cold, saturated ground immediately adjacent to retreating mountain snowbanks in late spring and early summer, this specialized cup fungus features deep, goblet-like apothecia clothed in a velvety layer of jet-black felt, playing an indispensable role in recycling organic matter in cold forest soils.
Biology and Physical Characteristics
The fruiting body of Plectania nannfeldtii consists of a deep, bowl- to goblet-shaped cup (apothecium) elevated on a slender, tapered black stem that anchors into buried conifer wood. The interior fertile surface (hymenium) is smooth, matte black to dark charcoal, while the exterior cup wall is covered in a dense, fine tomentum of short, dark fungal hairs that impart a distinctly fuzzy, felted texture. Inside the microscopic asci lining the cup, eight smooth, elliptical, hyaline ascospores develop, released into the mountain air through pressurized puffs as fluctuating humidity triggers the spore chambers to flex.
Behavior and Ecology
Functioning as an essential cryophilic saprotroph, the mycelium of Plectania nannfeldtii lives within buried, decomposing conifer debris—primarily needles, twigs, and rotting branches of Douglas fir, mountain hemlock, and Engelmann spruce. It initiates fruiting while snow is still actively melting, often emerging through patches of packed granular snow or ice. By breaking down tough, resin-saturated conifer lignins before warmer-season fungi become active, it initiates vital nutrient release that supports emerging alpine flora, mosses, and conifer seedlings.
Conservation and Human Impact
Plectania nannfeldtii is globally secure and evaluated as Least Concern, widely documented across undisturbed montane wilderness areas of the Rocky Mountains, Cascades, and Sierra Nevada. However, because its fruiting phenology is intimately synchronized with the timing and volume of high-altitude winter snowpack, it serves as a sensitive bioindicator of subalpine climate shifts. Protecting old-growth subalpine forests and undisturbed headwater snowmelt basins ensures the continued health of this unique cold-adapted fungal community.
Interesting Factoid
The Black Felt Cup often fruits right through the edge of melting snowbanks in subalpine forests, emerging with a velvety black coat that absorbs solar heat to accelerate its spore development.
Last updated: October 2026