Public Description of Piptoporus betulinus (Bull.) P. Karst.

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Name: Piptoporus betulinus (Bull.) P. Karst.
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 Draft For 2008/2009 Eol University Species Pages Initiative By Jered (Private)
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Description status: Unreviewed

Taxonomic Classification:

Domain: Eukarya
Kingdom: Fungi
Phylum: Basidiomycota
Class: Agaricomycetes
Order: Polyporales
Family: Fomitopsidaceae

General Description:

The fruiting body of Piptoporus betulinus has a pileus that is 1 1/8-10" (3-25.5 cm) wide with a shell, hoof, or kidney shape. The color is at first pale white, then acquiring a brownish tinge, and finally smoky grey with age. The surface of the cap often tears or breaks up into scales or patches as it ages. The most distinct feature of the fruiting body is the inrolled margin (most obvious at maturity), which remains as a rim around the pore surface.

The pore surface or hymenium is indented or depressed from the margin. When young the hymenium is cream colored and smooth, becoming pale brown to yellowish brown and jagged with age. The pores are circular to angular and there are 3-5/mm.

Although sometimes lacking, the stalk is lateral and up to 2 3/8" (6 cm), with a reddish-brown or brown color. The flesh is 3/8-2" (1-5 cm) thick, white, tough-fibrous, and corky.

Piptoporus betulinus is also known as the Birch conk or razor strop fungus. It was formerly called Polyporus betulinus.

Diagnostic Description:

Found strictly on dead or dying Birch trees, Piptoporus betulinus produces a white spore print. The spores are cylindric to sausage shape, smooth, hyaline and about 5-6 × 1.5-1.7 um in size.

The fungus causes a brown cubical rot and wood decayed by the fungus is said to have the smell of green apples.


Piptoporus betulinus can be found growing anywhere that Birch trees grow naturally. This limits them to the temperate climates of the northern hemisphere. It occasionally jumps to other host trees in the vicinity of birches.


Piptoporus betulinus is saprobic and can be found growing alone or gregariously on Birch wood. The fungus is an annual, growing anew each year. However, the fruiting bodies can found year round because they are tough and not easily degraded.

Look Alikes:

Polyporus squamosus resembles Piptoporus betulinus superficially, but the two are easily separated, since P. squamosus is very scaly on top with diamond shaped pores underneath. Polyporus squamosus does not grow on Birch trees and it causes a white rot.


Piptoporus betulinus has been dried and used as a razor strop to sharpen razors. It has also been used for medicinal purposes. The fungus contains strong purgatives, agaric acid and toxic resins, and antibiotics, acting against mycobacteria and metazoans. The fruiting bodies are also very good fire starters. Although the flesh is tough and fibrous the mushroom is edible when young but has a somewhat bitter taste.

In Fennoscandia large basidiocarps of this species were previously often used as a cushion for knives, which will not rust while standing in the fungus. Local names reflect this use.

The “iceman” Oetzi, found on the border of Italy and Austria, had this fungus in his pack, along with the other birch fungus, Fomes fomentarius. See Tom Volk’s page on Fomes fomentarius.


Barlow, Virginia. “Birch polypore, Piptoporus betulinus.” Northern Woodlands. 1 Mar. 2008. 13 Nov. 2008

Bessette, Alan E., Arleen R. Bessette, and David W. Fischer. Mushrooms of Northeastern North America. Syracuse, NY: Syracuse UP, 1997. 377.

Huffman, D. M., L. H. Tiffany, and G. Knaphus. Mushrooms & Other Fungie of the Midcontinental United States. Ames, Iowa: Iowa State UP, 1989.

Kuo, Michael. “Piptoporus betulinus.” MushroomExpert.Com. Jan. 2004. 13 Nov. 2008

McIlvaine,Charles and Macadam K. Robert. One Thousand American Fungi. New York, NY: Dover Publications, Inc., 1973. 488-89.

MycoBank entry on Piptoporus betulinus


Piptoporus betulinus is also known as the Birch conk or razor strop fungus.

It may be described as Polyporus betulinus as well.

Description authors: Tom Volk, jered (Request Authorship Credit)
Description editors: Nathan Wilson, Tim Adams

Created: 2008-12-25 17:07:11 PST (-0800) by Tom Volk (TomVolk)
Last modified: 2011-06-11 20:42:45 PDT (-0700) by Tim Adams (timonroad)
Viewed: 1628 times, last viewed: 2019-03-10 14:26:45 PDT (-0700)