Stereum hirsutum (Willd.:Fr.) Gray   

Kingdom: Fungi
Phylum: Basidiomycota
Subphylum: Agaricomycotina
Order: Russulales – russules, milk-caps and former 'Stereales'

British distribution: Widespread and common.
World distribution: Europe, Asia, North America.

Stereum hirsutum on Beech log
Stereum hirsutum on Beech (Fagus sylvatica) log, Midlothian, 1985.

An easily recognised and well known species, featuring on most field meeting ("foray") lists.

The fruit body (basidiocarp) is extended into 'brackets', though unlike most other 'bracket fungi' ('polypores'), the hymenium (spore-bearing tissue) is completely smooth rather than having the increased surface area conferred by pores or gills. The bracket shape itself provides an increased surface area and added protection to the hymenium. Resupinate growths of this species do occur, however, in which the fruit body is a simple crust without extending into brackets, almost the entire surface of the fungus being hymenium. Such growth forms are seen most often on undersides of branches and logs, where formation of horizontal brackets is not possible.

S. hirsutum is common on dead wood, almost always on deciduous species though rarely also on conifers (Eriksson et al., 1984). Beech (Fagus sylvatica) is a favoured host and, as shown in the photograph, the fungus can form large colonies on beech logs and stumps. It is readily found on many other species, on dead standing trunks, on fallen branches or even on small twigs on the forest floor.

It is usually easily recognisable by the combination of a roughly hairy upper surface and smooth, bright ochre-yellow hymenium. Unlike some related, duller-coloured species, the hymenium does not turn blood-red when it is scratched.

Sometimes (especially with age) the hymenium is not so brightly coloured and then it can be confused with S. rameale (= S. complicatum, S. ochraceoflavum, all these names in the sense applied in Britain), another non-reddening species which forms numerous small brackets (typically about 1 cm in length) on fallen twigs and dead branches. S. rameale never has the bright colours of typical S. hirsutum but undoubtedly it is overlooked, as well as sometimes wrongly claimed. The spores of S. rameale are 7-9 µm in length, compared with 6-7.5 µm in S. hirsutum.
S. rameale is locally common in southern England, but is uncommon in Scotland.

Recent molecular work has shown that Stereum and a few other corticioid (encrusting) genera (e.g. Peniophora), are related to the 'toadstool' milk-caps and russules and so current classification puts them together in the Russulales.

•   Eriksson, J., Hjortstam, K., & Ryvarden, L., (1988). The Corticiaceae of north Europe. 7: Schizopora - Suillosporium. Fungiflora, Oslo.

© A.J. Silverside
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