Butter Waxcap Identification Guide

The Grassland You Are Standing In

Waxcaps are habitat mushrooms before they are anything else, and the Butter Waxcap is no exception. When you find it you are almost always on old, unimproved grassland: a churchyard, a hillside pasture that has never been ploughed or fertilised, a mossy lawn that nobody has treated, a dune slack, or a woodland clearing with short grazed turf. The sward is short, the moss layer is thick, and the ground has been left alone for decades.

The first impression is of a small drop of butter or a smear of egg yolk sitting in the moss. It is a little mushroom, easy to walk past, and it usually appears with company: several fruit bodies scattered across a patch, and frequently other waxcaps of different colours nearby. Getting down on your knees is not optional with this species, because everything that identifies it is at the scale of a couple of millimetres.

Reading The Cap

The cap measures only 1 to 3 cm across, occasionally a little more. It starts convex or almost hemispherical and flattens out, often with a slight central depression in age, and the margin becomes wavy or lobed in older specimens.

The colour is a warm butter-yellow to golden or egg-yolk yellow, generally even across the cap rather than darker in the centre, though it can pale toward the margin as it dries. When moist the surface is faintly greasy or subtly tacky to the touch, but it is emphatically not slimy: your fingers do not come away coated, and no gluten string pulls between finger and cap.

Check the margin carefully with the cap held up against the light. In damp conditions the outer third is translucent-striate, meaning you can see the dark lines of the gills through the cap flesh, so the margin looks finely radially lined. That striation fades as the cap dries.

Reading The Gills

The gills carry the whole waxcap character and they are worth studying closely.

They are thick, soft and waxy in texture. Rub one between finger and thumb and it smears rather than crumbling, which is the sensation the family is named for. They are widely spaced, so you can count them easily, and the spaces between them are often bridged by low interveining on the gill faces, giving a slightly wrinkled, connected look under a lens.

Colour is pale yellow to whitish-yellow, generally paler than the cap.

Attachment is the character that does the most work. The gills are broadly attached to the stem and then run a short distance down it, so they are adnate with a decurrent tooth or shortly decurrent. Look at the junction in profile against the sky. You want to see the gill line dip downward onto the stem rather than notch upward away from it.

Stem, Base And Flesh

The stem is 2 to 5 cm long and only 2 to 4 mm thick, cylindrical, often slightly flattened or curved, and hollow when split. Colour matches the cap or is a shade paler, and the extreme base is frequently whitish.

Here is the single most useful field test for this species: touch the stem. It is dry, or at most very slightly moist. It is not glutinous, not slippery and not coated. Several closely related yellow waxcaps have stems that are conspicuously slimy, and running a finger down the stem separates them in one second flat.

The flesh throughout is thin, soft, waxy and yellow, concolorous with the surface. It shows no colour change when cut or bruised. Nothing blackens, reddens or greens, which itself rules out a set of waxcaps that do.

Taking A Spore Print

Small caps give small prints, so give this one time and a good background.

Select the largest and most mature cap you can find, one with a fully flattened or slightly depressed disc. Cut the stem away flush with the gills, set the cap gills-down on a piece of black card or dark glass, and cover it with a small cup to keep the humidity up. Because the cap is tiny, leave it overnight rather than a few hours.

The print is white. Read it against the dark background, where it shows clearly as a pale radial pattern. A white print on a small brightly coloured grassland mushroom with thick waxy gills is exactly what you expect from this family, and it eliminates the pink-spored and brown-spored grassland genera that occasionally produce yellowish caps.

Habitat, Ecology And Season

The Butter Waxcap fruits in short, mossy, nutrient-poor turf, and its presence is part of what makes a grassland a waxcap grassland. These fungi are strongly associated with mosses and with undisturbed soil that has not received fertiliser, and they respond very badly to ploughing, reseeding and nutrient enrichment. Because they take many years to establish, a good waxcap sward is effectively an indicator of long ecological continuity.

The season is autumn, typically from late summer into late autumn, peaking after rain when the turf has stayed damp for several days. Fruit bodies appear scattered or in small loose groups, often among other waxcaps in reds, oranges and whites, and they are short-lived.

Separating The Look-Alikes On Structure

Hygrocybe glutinipes is the classic confusion. It is the same size and much the same yellow, but both cap and stem are covered in a thick, obvious glutinous coating, so the stem is slippery and the fruit body is hard to hold. The Butter Waxcap has a dry stem.

Hygrocybe chlorophana is larger, brighter and more lemon to chrome yellow, with a distinctly viscid cap and a viscid or at least moist stem, and its gills are adnate to notched rather than running down the stem.

Hygrocybe insipida is similar in size but usually shows orange or reddish tones at the centre of the cap grading to yellow at the margin, and its stem base is often viscid.

Hygrocybe cantharellus has strongly and deeply decurrent gills, a scurfy or finely scaly cap surface, orange to red cap colours, and a much more funnel-shaped profile.

Gliophorus laetus has a slimy stem and a distinctly gelatinised gill edge visible as a translucent line under a lens.

Hygrocybe vitellina is a small yellow species with strongly decurrent gills and a markedly glutinous cap and stem.

Small yellow Galerina and Conocybe species may share the grassland but have brown to rusty spore prints, thin non-waxy gills and much more fragile stems.

Quick Field Checklist

Old, unfertilised, mossy short turf in autumn; cap 1 to 3 cm, even butter-yellow, faintly greasy but never slimy, translucent-striate at the margin when wet; thick, waxy, widely spaced pale yellow gills that run a little way down the stem, often interveined; dry yellow stem, hollow, paler at the base; yellow flesh with no colour change; white spore print.