Inonotus radiatus (Sowerby) P. Karst. - Alder Bracket

Phylum: Basidiomycota - Class: Agaricomycetes - Order: Polyporales - Family: Hymenochaetaceae

Inonotus radiatus - Alder Bracket, Scotland

Nearly always associated with dying alder trees, the tiered form of this pored fungus differentiates it from the (usually more massive) rounded fruitbodies of the Oak Bracket, Inonotus radiatus (synonym Mensularia radiata). Often the Alder Bracket appears well above head height. White rot results from attack by the Alder Bracket. (The young fruitbodies shown on the left were seen growing on the trunk of a riverside alder tree; this tough bracket fungus is fairly common on riverbanks that are lined by mature alders.

Inonotus radiatus, a mature Alder Bracket on a dying Alder tree, Wales

Distribution

Widespread but only locally common in Britain and Ireland, the Alder Bracket is also found throughout most of mainland Europe and in parts of North America.

The immature Alder Brackets shown on the left were seen growing on a dead Alder in Wales.

Taxonomic history

In 1799 British botanist-mycologist James Sowerby (1757 - 1822) described the Alder Bracket, giving it the binomial scientific name Boletus radiatus. (In the early days of fungal taxonomy many of the fungi with pores were placed in a gigantic Boletus genus, since largely redistributed to other genera.) It was in 1916 that Spanish mycologist Lázaro Ibiza (1858 - 1921) transferred this species to the genus Mensularia, establishing Mensularia radiata as what some mycologists (including the British Mycological Society) now accept as its preferred scientific name. Inonotus radiatus, the name that Finnish mycologist Petter Adolf Karsten (1834 - 1917) gave to the Alder Bracket in 1882, is the name you will find in most reference sources, however.

Inonotus radiatus, a mature Alder Bracket on a dead Alder tree

This species has several other synonyms including Boletus radiatus Sowerby, Polyporus radiatus (Sowerby) Fr.Fomes variegatus Secr., and Polystictus radiatus (Sowerby) Cooke.

Etymology

Inonotus, the genus name of the Alder Bracket fungus, comes from ino- a prefix meaning fibrous, and ot which means an ear; the ending -us merely turns it into the form of a Latinised noun.

The specific name radiatus comes from the Latin radi- meaning a ray, spoke or plate, and it is probably a reference to the radial wrinkles that are often evident on the upper surfaces of mature Alder Brackets.

Above: these mature, radially wrinkled Alder Brackets were seen growing on a dead Black Alder tree in Bulgaria.

Identification guide

Inonotus radiatus - injfertile upper surface

Upper (infertile) surface

Apricot coloured with slightly sunken reddish droplets near the margin when young, gradually turning brown and eventually almost black with age, with a pale rounded margin that becomes sharper as the fruitbody expands and matures. These semicircular or kidney-shaped brackets typically grow to 10cm diameter and stand out 3 to 6cm from the substrate wood. Their thickness is very variable but commonly in the range 1 to 3 cm; however, fruitbodies are nearly always tiered and they tend to merge one with another.

The cap surface is finely velvety at first, becoming smmoother with warty lumps and radial wrinkles. The flesh is rusty brown and very tough.

Pores of Inonotus radiatus

Tubes and Pores

The rust-brown tubes, spaced at 2 or 4 per mm, are typically 3 to 10mm deep and terminate in silvery-cream irregularly rounded or angular pores. With age, the pores turn buff and then brown.

 

Spores

Broadly ellipsoidal, smooth, 4.5-6.5 x 3.5-4.5μm; inamyloid or weakly dextrinoid.

Spore print

Pale yellowish-brown.

Odour/taste

Odour not distinctive; taste rather bitter.

Habitat & Ecological role

On dead or dying deciduous hardwood trees, mostly alders but sometimes on birches and Beech and very occasionally on other hardwood trees.

Season

Annual brackets persist in blackened form throughout the year, but new young brackets generally appear in early to mid summer and release their spores during late summer and autumn.

Similar species

Pseudoinonotus dryadeus, the Oak Bracket, produces larger brackets and weeps dark-honey-coloured droplets much more copiously; it does not usually produce tiers of fruitbodies and it is found mainly on the basal roots and lower trunks of oak trees.

Inonotus radiatus, mature Alder Brackets on a dying Alder tree, West Wales

Culinary Notes

Alder Bracket Inotus radiatus is as bitter, tough and inedible as the bark of the alder tree on which it grows, and so it can have no culinary value.

Reference Sources

Pseudoinonotus T. Wagner & M. Fisch., Mycol. Res. 105(7): 781 (2001)

Mattheck, C., and Weber, K. Manual of Wood Decays in Trees. Arboricultural Association 2003.

Pat O'Reilly, Fascinated by Fungi, 2016.

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

BMS List of English Names for Fungi

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.

Other web pages about this species

Leif Goodwin (UK)

Michael Kuo (USA)

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