Armillaria borealis Marxm. & Korhonen

Phylum: Basidiomycota - Class: Agaricomycetes - Order: Agaricales - Family: Physalacriaceae

Armillaria borealis

There are many forms of Honey Fungus, and in the distant past they all shared the scientific name Armillaria mellea. Nowadays it is generally accepted that there are several distinct species, one of which, Armillaria borealis, was only recognised as recently as 1982.

Armillaria borealis has a very catholic taste for timber, appearing (generally quite high up) on a wide range of broadleaf and coniferous trees, including (as seen here) pines.

Distribution

This species is a very rare find in Britain and Ireland; it has been recorded most often in Scotland but there are several records from England and at least one from Ireland. Elsewhere in Europe it is most often seen in Finland and occurs occasionally in other northern countries at least as far south as France and the Netherlands. It seems likely that many finds go unrecorded, as it is easy to confuse this rare species for the much more common and widespread Honey Fungus Armillaria mellea.

Taxonomic history

This woodland mushroom was accepted as a separate species, Armillaria borealis, following a 1982 publication in France by German mycologist Helga Marxmüller and Finnish mycologist Kari Korhonen.

Etymology

The specific epithet borealis comes from the Greek noun boréas which means 'north wind'; Borealis means 'of the north', and indeed records show that Armillaria borealis is most common in northern parts of Europe.

Toxicity

Although all Armillaria species were for many years generally considered edible when thoroughly cooked, some members of the honey fungus group (including Armillaria mellea, the type species of this genus) that occur on hardwoods are considered by some to be suspect, as cases of poisoning have been linked to eating these fungi; this is most probably due to a small but significant proportion of people being adversely affected rather than a universal human reaction to these fungi. We therefore recommend that Armillaria borealis, which in any case is a rare species in Britain and therefore worthy of conservation, should not be collected for the pot.

Identification guide

Cap of Armillaria borealis

Cap

2 to 8cm in diameter; orange-brown, sometimes with an olive tinge, and with a darker brown central area; hygrophanous, drying paler from margin; initially convex then flattening, often with a broad umbo; surface covered with small brown pointed scales.

The cap flesh is whitish and firm.

Gills of Armillaria borealis

Gills

The adnate or weakly decurrent gills are crowded and initially almost white, gradually becoming cream and then orange tinged with scattered brown rust-like spots at maturity.

Stem

Palest at the apex; colour as cap below the ring, darkening as the fruitbody matures; 4.5 to 12cm long; slender, with a clavate base.tapering towards the apex. Surface with persistent yellowish woolly scales, largest near the ring and progressively smaller towards the base. There is a persistent thick but narrow ring, with a yellow edge/underside but no dark spots (see Armillaria ostoyae). Stems usually emerge from timber in small tufts. Stem flesh is whitish.

 

Basidia

Usually four-spored, clavate, with basal clamps (unlike Armillaria mellea, whose basidia do not have basal clamps).

Spores

Ellipsoidal, smooth, usually with guttules; 7.5-10 x 5-7µm; amyloid.

Spore print

Very pale cream.

Odour/taste

Slight 'mushroomy' odour; taste initially mild then gradually unpleasant.

Habitat & Ecological role

Parasitic (and later saprobic) on standing broadleaf and coniferous trees; also occasionally seen on dead stumps. Nearly always the fruitbodies appear well above ground level and often high up on the trunks particularly of birches.

Season

Late summer and autumn in Britain and Ireland.

Similar species

Armillaria mellea, commonly referred to as Honey Fungus, generally has a much chunkier persistent stem ring.

Pholiota squarrosa grows low down on hardwood trees; it is generally similar in colour and covered in scales; it retains an in-rolled margin, the gills turn uniformly rusty-brown, and it has a radish-like smell and taste.

Armillaria borealis, southern England

Reference Sources

Flora Agaricina Neerlandica: Critical Monographs of Families of Agarics and Boleti occuring in the Netherlands Vol. 3, Tricholomataceae (Ed.: C.Bas, Th.W. Kuyper, M.E. Noordeloos & E.C. Vellinga)

Dictionary of the Fungi; Paul M. Kirk, Paul F. Cannon, David W. Minter and J. A. Stalpers; CABI, 2008

Taxonomic history and synonym information on these pages is drawn from many sources but in particular from the British Mycological Society's GB Checklist of Fungi and (for basidiomycetes) on Kew's Checklist of the British & Irish Basidiomycota.

Acknowledgements

This page contains pictures shown with the kind permission of Simon Harding.

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