Polyporus tuberaster (Jacq.) Fr. - Tuberous Polypore

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

Polyporus tuberaster - Tuberous Polypore, picture by David Kelly

An uncommon find, the Tuberous Polypore grows on fallen branches of deciduous hardwood trees. It is reported that sometimes these funnel-shaped polypores grow from a sclerotium-like tuber (a hard mass of mycelium that stores food reserves, enabling the fruitbody to survive harsh environmental conditions).

These woodland fungi are easily overlooked, as often the caps are darker than those on the left and blend in with a background of dead leaves.

Polyporus tuberaster - Tuberous Polypore, pale capped form

Distribution

Polyporus tuberaster is seen only infrequently in Britain and Ireland. It occurs also across most of mainland Europe and in many parts of Asia.

Taxonomic history

The Tuberous Polypore was described in 1796 by Dutch naturalist Nicolaus Joseph von Jacquin (1727 - 1817), who gave it the binomial scientific name Boletus tuberaster. It was the Swedish mycologist Elias Magnus Fries who, in 17821, redescribed this species and transferred it to the genus Polyporus, thus establishing its currently-accepted scientific name Polyporus tuberaster.

Synonyms of Polyporus tuberaster include Boletus tuberaster Jacq., Favolus boucheanus Klotzsch, Polyporus lentus Berk., Polyporus coronatus Rostk., Polyporus floccipes Rostk., Polyporus boucheanus (Klotzsch) Fr., and Polyporus forquignonii Quél.

Polyporus tuberaster - Tuberous Polypore, west Wales 2017

Etymology

The generic name Polyporus means 'having many pores', and fungi in this genus do indeed have tubes terminating in pores (usually very small and a lot of them) rather than gills or any other kind of hymenial surface.

The specific epithet tuberaster means 'with tubers', and in the case of the Tuberous Polypore this is a reference to tuber-like lumps of hyphae from which these funnel-shaped fungi emerge.

The tubers are reputed to store essential food substances necessary for the fungi to survive in harsh environments. (In Britain's temperate climate Polyporus tuberaster may not need such an insurance policy, but perhaps evolution has equipped it to cope with extremes of climate change yet to come) Round, oval or irregular in shape, the tubers are ochraceous and fleshy when fresh, shrinking considerably if they dry out.

Other polypores that either mainly or at least sometimes have central (or nearly central) stems include Albatrellus ovinus, Albatrellus subrubescens, Polyporus brumalis, and Phaeolus schweinitzii as well as some of the bracket fungi - particularly in the genera Trametes, Bjerkandera and Meripilus.

Identification guide

Cap of a pale form of the Tuberous Polypore

Cap

5 to 10cm across; round rather than bracket shaped; slightly or deeply funneled; light brown to dark orange-brown and covered in small scales, sometimes concentrically zoned; the thin margin is often downturned or inrolled.

Stem

Rudimentary, pale; reported to be attached to a sclerotium in some instances (but certainly not generally so in Britain and Ireland); hairy near the base.

Pore surface of Polyporus tuberaster

Tubes and pores

Tubes are creamy-white, 1-4mm deep, terminating in white or cream angular pores spaced at 1-3 per mm, decurrent and so leaving very little bare stem.

Pores of Polyporus tuberaster

Spores

Cylindrical, smooth, 12-16 x 4-6µm; inamyloid.

Show larger image

Spore print

White.

Odour/taste

Odour slightly mushroomy; taste mild but not distinctive.

Habitat & Ecological role

Saprobic, most often found growing on buried rotten hardwoods, particularly Beech.

Season

Summer and autumn.

Similar species

Dryad's Saddle, Polyporus squamosus, occasionally forms trumpet-shaped fruitbodies arising from roots under the leaf litter; however, it has a black stem base and larger cap scales than the Tuberous Polypore.

Culinary Notes

When young the fruitbodies of the Tuberous Polypore are said to be edible and quite good, but we have no first-hand experience of eating these fungi and we know of no recipes specifically devised for them.

Polyporus tuberaster - Tuberous Polypore, west Wales, a dark specimen

Reference Sources

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

Ellis, J. B.; Ellis, Martin B. (1990). Fungi without gills (hymenomycetes and gasteromycetes): an identification handbook. London: Chapman and Hall. ISBN 0-412-36970-2

Pat O'Reilly (2016). Fascinated by Fungi, First Nature Publishing

BMS List of English Names for Fungi

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

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)

Acknowledgements

This page includes pictures kindly contributed by David Kelly.

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