Sweetbread Mushroom
Clitopilus prunulus
Also called the miller, miller mushroom, miller's mushroom
A white, matt, suede-textured woodland mushroom with decurrent gills that turn pink and a strongly farinaceous odour. The pink spore print and running gills are its defining combination.
Overview
The Sweetbread Mushroom (Clitopilus prunulus), long known as The Miller, is a distinctive medium-sized white agaric of woodland edges and clearings. Its cap has an unusual surface texture — dry, matt and softly suede-like or kid-leather in feel, quite unlike the silky or greasy caps of similar white species — and the cap outline is often irregular, lobed and wavy with an inrolled margin.
The two characters that clinch it are the gills and the spores. The gills run distinctly down the stipe (decurrent) and shift from white to a soft flesh-pink as the spores mature, and the spore print is a clear pink. Under a microscope the spores are longitudinally ridged and appear angular in end view, a feature shared with the pinkgills but combined here with decurrent gills.
The common name The Miller refers to its strong farinaceous odour, reminiscent of a working grain mill. That smell is noticeable from a short distance in a good group and is a useful supporting character when working through white woodland agarics.
How to identify it
Cap
3 to 10 cm across, convex then flattened and often becoming shallowly depressed, frequently irregular, lobed or wavy at the margin, which stays inrolled for a long time. The surface is dry and matt with a fine suede-like or chamois texture, white to pale cream or greyish, sometimes with a faint bloom.
Gills
Decurrent, running noticeably down the stipe, moderately crowded and fairly narrow. They are white at first and become a soft flesh-pink or salmon as the spores ripen. The gills detach easily from the cap flesh when rubbed.
Stipe
Short in proportion to the cap, 2 to 6 cm tall and 0.5 to 1.5 cm thick, white, solid, often slightly tapered downwards and frequently attached off-centre. It is finely fibrillose to minutely powdery at the apex. There is no ring and no volva.
Flesh & spore print
The flesh is white, soft and unchanging when cut, with a strong farinaceous odour. The spore print is pink to salmon-pink, and the spores are ellipsoid with longitudinal ridges, appearing angular when viewed end-on.
Where and when it grows
This species fruits on soil in woodland clearings, along rides and path edges, on grassy woodland margins and in adjacent pasture near trees. It occurs with a range of broadleaved trees including oak, beech, birch and hazel, and also in conifer plantations, usually in short vegetation or moss rather than deep leaf litter.
The season runs from midsummer through autumn, with the main flush in August to October. It is widespread and reasonably frequent across Europe, with records from North America and temperate Asia. Fruitbodies appear singly, scattered or in small groups.
Ecological role
The trophic status of Clitopilus prunulus has been debated. It was long listed as a saprotroph of woodland soil, but its consistent association with trees, and experimental and molecular evidence, point to an ectomycorrhizal or at least tree-associated habit, and it is now generally treated as ectomycorrhizal. Its habit of fruiting in grassy clearings close to woodland edges fits a partnership with tree roots extending beyond the canopy.
The genus Clitopilus is closely related to Entoloma within the Entolomataceae, which explains the shared pink spore print and ridged, angular spores; the decurrent gills and matt cap distinguish Clitopilus within that family. Spores fall from the running gills and are dispersed by air currents beneath the low, often depressed cap.
Similar species
Clitocybe nebularis is much larger and more robust with a grey to grey-brown cap, only slightly decurrent gills and a white spore print. Small white Clitocybe species such as C. rivulosa and C. dealbata have decurrent gills and a white cap, but their caps have a frosted or faintly zoned surface rather than a suede texture, their gills stay white or cream, and they give a white spore print — taking a print is the decisive test.
Entoloma sinuatum, the Livid Pinkgill, is far larger, with an ivory to yellowish-grey cap, and its gills are sinuate or adnexed, not decurrent, though it shares a pink print and a farinaceous odour. Clitopilus scyphoides is much smaller and more funnel-shaped. Any white agaric with decurrent gills should be printed, since the pink deposit of Clitopilus versus the white deposit of Clitocybe is the single clearest separator.