Rhodocollybia butyracea - Butter Cap

Taxonomy

Phylum: Basidiomycota

Class: Agaricomycetes

Order: Agaricales

In terms of its cap colour, Rhodocollybia butyracea (syn. Collybia butyracea), commonly referred to as the Butter Cap or Greasy Toughshank, is a very variable fungus. It occurs in all types of woodland, often in groups or fairy rings.

Some authorities recognise two varieties of this mushroom depending on the colour. The dark-centred var. asema is illustrated in the main picture, and var. butyracea is shown below.

In the past more commonly known as Greasy Toughshank, this mushroom is nowadays referred to as the Butter Cap.

Sometimes found in deciduous woodland, Rhodocollybia butyraceae is mainly associated with coniferous forests on acid soils, where it grows in large numbers beneath even the darkest of canopies.

Identification Guide

Cap

Tremendously variable in cap colour, between reddish-brown and pale grey, the caps of this species are initially convex, flattening but with a slight umbo and often turning up at the edge when fully developed. The cap diameter at maturity ranges from 4 to 9cm

There are many forms of this species, and cap colour in particular is a poor guide to identification. All Butter Caps tend to become much paler when dry.

	Gills The crowded adnexed or sometimes free gills are white or very pale cream. Towards the end of the season, the cap cuticles of mature specimens appear to contract slightly so that the gills flare upwards at the edge.
	Stem Of the same general colour range as the cap, but paler at the top and often covered in fine white hairs near the base, the stem tapers in noticeably towards the apex. At the base of the stem, which is often bent where it enters the soil, there is a spongy bulb. The stem is very tough and not easily separable from the cap.
Spore print	Cream-buff.
Odour/taste	Not distinctive.
Habitat	Mainly under conifers but occasionally also in deciduous woodland.
Season	June to December.
Occurrence	Very common.
Similar species	Rhodocollybia prolixa (syn. Collybia distorta) is a much less common mushroom of conifer forests; it has a dry, red-brown cap and a swollen base below a fibrous and often slightly twisted stem. Rhodocollybia maculata is usually paler and has brown-spotted gills.