Field Bird's Nest
Cyathus olla
Also called common bird's nest, flared bird's nest, olla bird's nest
A small grey goblet with a widely flaring, often wavy mouth and a smooth inner wall, holding a few unusually large lead-grey discs. It favours open ground and plant litter rather than deep woodland.
Overview
Cyathus olla is the bird's nest fungus most likely to be met away from woodland: on bare soil, stubble, garden beds, sand dunes and among the remains of herbaceous plants. Its cup is broader and more openly flared than that of its relatives, with the rim often turned outwards and slightly wavy, so the whole structure resembles a small goblet or the earthenware pot the epithet refers to.
Like all members of the Nidulariaceae it belongs to the Agaricales and produces its spores inside lens-shaped peridioles held in the cup. In C. olla those peridioles are notably large — often 2.5–3.5 mm across — and comparatively few in number, so a mature cup may hold only a handful of conspicuous grey discs.
The smooth, unfurrowed inner wall is the quickest way to separate it from the fluted bird's nest, and the pale greyish, only finely felted exterior contrasts with the shaggy brown of that species. It is a common and widely distributed fungus that is easily overlooked because of its size.
How to identify it
Fruiting body
A cup 8–15 mm tall and up to 10–15 mm wide at the mouth, distinctly funnel- to goblet-shaped, tapering to a narrow base. The mouth flares outwards more strongly than in other Cyathus species and is frequently wavy or irregularly turned back. Cups occur singly, scattered or in loose groups.
Outer surface
Greyish-brown to dull ochre or pale tan, finely woolly to felted when fresh, becoming smoother and greyer with weathering. It never carries the coarse, spiky, dark shaggy hairs of Cyathus striatus.
Inner surface
Smooth and unfurrowed — no grooves or pleats — pale grey to lead-grey or silvery, sometimes with a faint sheen.
Lid and peridioles
A whitish membrane closes the young cup and tears away as it matures. Inside are relatively few peridioles, commonly 4–10, but each is large for the group at roughly 2.5–3.5 mm across: flattened, disc-like, grey to blackish, with a thin paler outer skin. Each is fastened by a coiled funiculus cord. Spores develop within the peridioles, so no ordinary spore print is produced.
Where and when it grows
This species prefers open, disturbed and often sunlit ground rather than shaded woodland. Typical sites include arable field margins and stubble, garden borders, vegetable plots, roadside soil, sandy waste ground, coastal dunes and the litter of dead stems, straw and old plant stalks. It also colonises wood chip mulch, though less exclusively than its woodland relatives.
Cyathus olla is widespread and frequent across Europe, North America, Asia, North Africa and Australasia, tolerating drier and more exposed sites than most bird's nest fungi. Fruiting bodies appear from summer into late autumn and the tough cups can persist for a considerable time afterwards.
Ecological role
Cyathus olla is a saprotroph. Its mycelium decomposes dead herbaceous stems, straw, crop residues, buried plant fragments and small woody debris, playing a modest but real part in recycling litter on cultivated and disturbed land.
Spore dispersal follows the splash-cup principle shared by the family: a raindrop striking the sloped inner wall is deflected upwards and hurls one or more peridioles clear of the cup. The trailing funiculus stretches into a sticky thread that can wrap around a nearby stem, fixing the package where it may later be taken up by grazing animals or simply break down in place, freeing the spores. The unusually wide, flaring mouth of this species presents a large target for incoming drops.
Similar species
Cyathus striatus is the most frequent confusion but is easily settled: it has strong lengthwise grooves inside the cup, coarse shaggy dark brown hair outside, a narrower, less flaring shape and more numerous, smaller peridioles. Cyathus stercoreus also has a smooth inner wall but is darker, narrower, hairier when young, holds many small jet-black peridioles, and grows on dung or heavily manured ground.
Crucibulum laeve differs in being a squatter, more cylindrical crucible with a bright ochre to cinnamon felty exterior, a smooth pale interior and whitish peridioles. Nidula species have numerous small pale peridioles embedded in a gelatinous layer with no funiculus cord at all. Very young unopened cups of any of these are hard to name until the lid ruptures.