Heterobasidion annosum (Fr.) Bref. - Root Rot

Phylum: Basidiomycota - Class: Agaricomycetes - Order: Polyporiales - Family: Bondarzewiaceae

Heterobasidion annosum - Root Rot

One of the most serious parasites of conifers, Root Rot is a cause of major economic loss to the conifer forestry industry. Broadleaf trees are not entirely immune to Root Rot: occasionally this root-rotting perennial bracket infects Beech trees and once in a while birches too.

The tough fruitbodies of Fomes Rot, as many forestry managers still call it (an earlier synonym for this species was Fomes annosus), occur low down on the buttress roots.

Heterobasidion annosum, Root Rot at the base of a spruce tree

Trees become infected via wounds to the bark, where the sapwood of buttress roots is exposed. Stumps of freshly felled trees are an open invitation to this fungus, whose mycelium spreads from one tree to another where the roots of adjacent trees rub against one another.

Distribution

A very common and widespread root bracket fungus in Britain and Ireland, Heterobasidion annosum occurs throughout mainland Europe and is also reported to be very common in many parts of North America.

Taxonomic history

When the great Swedish mycologist Elias Magnus Fries described this bracket fungus in 1821 he gave it the binomial scientific name Polyporus annosus. The currently-accepted scientific name of this species dates from an 1888 publication by the German mycologist Julius Oscar Brefeld (1839 - 1925).

Heterobasidion annosum has many synonyms including Boletus cryptarum Bull., Polyporus annosus Fr., Polyporus cryptarum (Bull.) Fr., Poria cryptarum (Bull.) Gray, Fomitopsis annosa (Fr.) P. Karst., Fomes annosus (Fr.) Cooke, Fomes cryptarum (Bull.) Sacc., and Spiniger meineckellus (A. J. Olson) Stalpers.

Etymology

Heterobasidion, the generic name, means 'with variable basidia'. The specific epithet annosum comes from the Latin annus and means aged (many years old - perennial in other words).

Identification Guide

Heterobasidion annosus, Root Rot fungus, top view

Fruitbody

Brown, corrugated upper surface blackening with age; narrow, round-edged brackets; sometimes in tiers and occasionally resupinate; downy when young, then smooth but uneven or knobbly. The individual brackets are 5 to 30cm across and 1 to 2cm thick, often with a wavy margin.

 

Heterobasidion annosus, Root Rot fungus, underside view

Tubes and pores

The tubes are off-white, and they terminate in creamy white round pores that are spaced at between 2 and 4 per mm.

A new tube layer 2 to 5mm thick grows each year.

 

 

Spores

Broadly ellipsoidal to subglobose, very finely warty, 4.5-6 x 3.5-4.5µm; inamyloid.

Spore print

Cream or pale yellow.

Odour/taste

Not distinctive.

Habitat & Ecological role

Parasitic on the lower trunks and buttress roots of conifers and very occasionally on some hardwood trees.

Season

June to November in Britain and Ireland.

Similar species

Gannoderma australe has a thicker fruitbody and releases brown spores.

Culinary Notes

This bracket fungus is extremely tough and certainly quite inedible.

Reference Sources

Fascinated by Fungi, Pat O'Reilly 2016.

British Mycological Society (2010). English Names for Fungi

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.

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