Variable Oysterling Identification Guide

Standing in the Right Place

Variable Oysterling is a mushroom you find by crouching, not by scanning. The setting is almost always damp broadleaf woodland, a shaded hedge bottom, a nettle bed at the edge of a wood, or the litter-choked margin of a woodland path. What you are looking for is small twigs, bramble runners, dead herbaceous stems and thin fallen branches lying on wet leaf litter. Turn a few of them over. When the species is fruiting it is rarely shy: a single twig can carry twenty or thirty tiny white shells in a row, sometimes overlapping like scales.

The first impression is of white flecks, no bigger than a fingernail, clinging sideways to wood with no visible stalk. Because most of them grow on the underside of a twig so their gills face the ground, a twig that has rolled since the fruit bodies formed will show caps twisted at odd angles, gills half skyward. That habit of forming on the shaded underside is itself a useful early hint.

Reading the Cap

Measure it. A typical cap is 0.5 to 2 cm across, occasionally reaching 3 cm on a rich substrate. The shape is shell-like, kidney-shaped, fan-shaped or almost circular with a lateral attachment, and it is genuinely inconstant from one fruit body to the next; the epithet records exactly that plasticity.

Colour is white to cream and, importantly, stays white. It does not become brown, tan or greasy-looking with age the way several relatives do. The surface is dry and matt. Put a hand lens on it and you should see a short, soft, white felt or down, densest near the point of attachment. Run a fingertip across the cap: it feels velvety-dry, never slippery.

Two negative characters matter. First, the margin is not translucent-striate; you should not see the gills showing through as dark radial lines when the cap is held up to the light. Second, there is no gelatinous, rubbery pellicle. If you pinch the cap surface between thumb and finger and try to stretch it, the flesh tears; it does not peel away as an elastic skin.

Attachment, Base and Flesh

There is no true stipe. The fruit body is sessile, or at most narrowed to a tiny lateral stalk-like point, and there is often a small patch of white mycelial down radiating from that point onto the bark. There is no ring and no volva. The flesh is very thin, soft, white and watery, and the whole fruit body collapses to a shrivelled scrap within a day of drying out, reviving poorly.

The Gills and What They Tell You

Gills radiate from the attachment point, spreading fan-wise. They are moderately close to slightly distant, narrow, and their colour is the single most useful field character after the spore print itself. Young gills are white. As the spores mature they shift through pale pinkish-buff to ochraceous, then to a dull cinnamon or clay brown. Under a lens, the gill edges look finely fringed rather than clean-cut.

That browning is your first evidence that this is a brown-spored fungus. Every white sessile mushroom you meet on twigs looks the same when young; only the maturing gills, or a print, separate the brown-spored Crepidotus from the white-spored imitators.

Taking a Spore Print from Something This Small

Standard paper-and-glass technique works, but the caps are so thin that they dry before they drop. Detach a cap that already shows brownish gills, keeping the attachment point intact. Lay it gills-down on a glass microscope slide or a strip of white card, place a drop of water on the upper surface, and cover the whole thing with an upturned glass or a small pot to hold humidity. Leave it three to six hours, or overnight.

The deposit is pale brown, ochre-brown, sometimes with a faint pinkish cast. It is never white. Judge it by scraping the deposit into a small heap with a knife tip, since a thin scatter of brown spores on white card can read as grey.

If you have a microscope, this species can be finished in one slide. The spores are allantoid, that is cylindrical and slightly curved like a small sausage, roughly 5.5 to 7.5 by 2.5 to 3.5 micrometres, with a minutely roughened wall. Almost every other common member of the genus has globose, subglobose or plainly ellipsoid spores, so a curved cylindrical spore in a small white sessile fungus is close to conclusive. The gill edge carries abundant cystidia of irregular, often flexuous or lobed shapes.

Substrate and Season

The substrate is small-diameter dead material: fallen twigs and thin branches of broadleaf trees, and also the dead stems of herbaceous plants such as nettle, bramble, willowherb and umbellifers, plus dead fern rachises. It is a recycler of woodland litter rather than a colonist of big logs, and it is one of the reasons that turning over the small stuff is more productive than examining stumps.

Fruiting runs from summer through late autumn, and in mild oceanic winters it can appear in any damp spell. Flushes follow rain within a few days and vanish quickly, so wet weeks are the time to look.

Separating It from the Look-alikes

Work through these on structure alone.

Crepidotus cesatii is the hardest. It is equally small, white and sessile, often with a slightly better-developed stalk-like base and a hairier attachment. Macroscopically the two overlap badly; the spores decide it, being globose to subglobose and distinctly warted rather than curved and cylindrical.

Crepidotus applanatus is bigger, up to 4 cm, more evenly fan-shaped, hygrophanous, and its cap margin is translucent-striate when moist. It tends to grow in overlapping tiers on rotten logs rather than singly on twigs, and its spores are globose.

Crepidotus mollis is much larger and browner, and its cap has a gelatinous elastic layer that stretches like thin rubber when pulled. It is a log and stump species.

Crepidotus luteolus and C. epibryus are narrower, more tongue-shaped, often attached along a line rather than at a point, and favour grass stems, rushes and moss.

Cheimonophyllum candidissimum is chalk-white and stays white, but gives a white spore print and has a slightly gelatinised flesh.

Resupinatus applicatus is grey to blackish, cup-like and gelatinous, attached by a central point on the back. Plicaturopsis crispa has folded, blunt, vein-like false gills and a crisped orange-brown cap. Schizophyllum commune has grey hairy caps and split, in-rolled gill edges. Any very young Pleurotus is an order of magnitude larger and drops a white print.

A Repeatable Field Routine

Find white sessile fungi on thin dead stems. Check the cap is dry, downy and not striate. Check the flesh is not gelatinous. Note the gill colour: white, buff or brown. Take a humid print overnight and confirm it is pale brown. Then, if you can, put one gill on a slide and look for curved cylindrical spores. Habitat plus a brown print gets you to the genus with confidence; the spore shape closes the case.