Minnesota Seasons - Milk-white Toothed Polypore

Conservation • Description • Habitat • Ecology • Distribution • Taxonomy

Conservation Status

Photo by Luciearl

IUCN Red List

not listed

NatureServe

not listed

Minnesota

not listed

Description

Milk-white Toothed Polypore is widespread in Europe and North America. It is very common in the eastern United States to the Midwest, including Minnesota, but rare in the Southwest. It grows flat (resupinate) on the bottom and sides of logs and fallen branches of hardwood trees, infrequently also on conifers. It usually obtains its nutrients from dead wood (saprobic), possibly also from live cherry wood (parasitic). It is exceptionally resistant to pollution toxicity.

The fruiting body is a patch of pore surface spread out flat (effused) on a branch or log (substrate). It is dry, stiff, and white, off-white, or cream-colored. Adjacent patches often fuse together creating a long row. There are 2 or 3 pores every thirty-second of an inch (1 mm). The pore walls are thin and disintegrate unevenly. As the walls break down the spore surface becomes maze-like. Eventually, only flattened, tooth-like projections less than ¼″ (6 mm) long remain. When growing on the side of a log or branch it may develop shelf-like caps. If present, the cap is ⅜″ to 1½″ wide, whitish to grayish, often concentrically zoned, and densely covered with velvety hairs. There is no stem. The flesh is thin and tough. It is not edible.

Similar Species

Habitat and Hosts

Dead hardwood logs and branches

Ecology

Season

Annual but persists year-round

Distribution
		Sources 7, 24, 26, 29, 30, 77. Biodiversity occurrence data published by: Minnesota Biodiversity Atlas (accessed through the Minnesota Biodiversity Atlas Portal, bellatlas.umn.edu, XX/XX/XXXX).
3/5/2025

Occurrence
Widespread and very common

Taxonomy
Kingdom	Fungi (fungi)
Subkingdom	Dikarya
Division	Basidiomycota (club fungi)
Subdivision	Agaricomycotina (jelly fungi, yeasts, and mushrooms)
Class	Agaricomycetes (mushrooms, bracket fungi, puffballs, and allies)
Subclass	Agaricomycetidae
Order	Polyporales (shelf fungi)
Family	Irpicaceae
Genus	Irpex

There is wide disagreement about the family to which the genus Irpex belongs. MycoBank and NCBI place it in Irpicaceae, Fungi Growing on Wood (Gary Emberger, Messiah College) in Phanerochaetaceae, Encyclopedia of life in Meruliaceae, and MushroomExpert in Steccherinaceae. Until 2019, Index Fungiforum placed it in Meruliacea, but they very recently transferred it to the family Irpicaceae.

Subordinate Taxa


Synonyms
Boletus cinerascens Boletus tulipiferae Coriolus lacteus Coriolus tulipiferae Daedalea diabolica Hirschioporus lacteus Hydnum lacteum Irpex bresadolae Irpex diabolicus Irpex hirsutus Irpex lacteus Irpex pallescens Irpex sinuosus Irpiciporus lacteus Irpiciporus tulipiferae Microporus chartaceus Microporus cinerascens Polyporus chartaceus Polyporus tulipiferae Polystictus bresadolae Polystictus chartaceus Polystictus cinerascens Polystictus cinerescens Polystictus tulipiferae Poria cincinnati Poria tulipiferae Sistotrema lacteum Steccherinum lacteum Trametes lactea Xylodon bresadolae Xylodon hirsutus Xylodon lacteus Xylodon pallescens Xylodon sinuosus

Common Names
Milk-white Toothed Polypore

Glossary

Resupinate

In fungi: referring to the fruiting body lying flat on the surface of the substrate, without a stalk or a cap.

Saprobic

A term often used for saprotrophic fungi. Referring to fungi that obtain their nutrients from decayed organic matter.

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Irpex lacteus
Amadej Trnkoczy

About

Album description

Irpex lacteus (Fr.; Fr.) Fr. Elench. Fung. p145, 1828, syn.: Sistotrema lacteum Fr.
Milk-white toothed polypore, DE: Milchweisser Eggenpilz
Slo.: belkasti rašpovec

Dat.: Feb. 23. 2014
Lat.: 46.35947 Long.: 13.70424
Code: Bot_784/2014_DSC0038
File names: from Irpex-lacteus_raw_1.xxx to Irpex-lacteus_raw_8.xxx.

and

Dat.: Feb. 27. 2014
Lat.: 46.35947 Long.: 13.70424
Code: Bot_786/2014_DSC0132
File names: from Irpex-lacteus_raw_10.xxx to Irpex-lacteus_raw_11.xxx.

Habitat: alpine valley, an opening in mixed forest with predominantly Fagus sylvatica followed by Picea abies; modestly inclined southeast oriented mountain slope, overgrown calcareous ground composed of scree, rocks and boulders; mostly in shade, partly protected from direct rain by tree canopies; average precipitations ~ 3.000 mm/year, average temperature 7-9 deg C, elevation 560 m (1.950 feet), alpine phytogeographical region.

Substratum: cut down trunk of Fagus sylvatica lying on ground, in its late initial phase of integration; the trunk was massively infected also with Trametes hirsutum.

Place: Lower Trenta valley, between villages Soča and Trenta, right bank of river Soča, near 'Na melu' place, East Julian Alps, Posočje, Slovenia EC.

Comments: fruit body mostly resupinated but also effused-reflexed; very large, about 1.5 m x 20 cm, about 2-3 mm thick, context thinner than pore layer; small 'pilei' up to 8(12) mm off the substrate; hymenophore with initially distinctly irregular angular, almost labyrinthine pores soon becomes irpiciform to hydnoid (compare Figs. 8. and 10.); smell indistinctive, taste initially indistinctive, after some time slightly unpleasant; 5% KOH reaction on context and pore layer mild, color changed to somewhat darker ocher-beige; SP abundant, white-yellowish with a slight green tint, oac014. No hypha clamps have been observed. All observed traits fit well to expectations for Irpex lacteus except cystidia. The fact that I haven't found conspicuously encrusted cystidia puzzles me.

Spores smooth. Dimensions: 5.1 [5.9 ; 6.2] 7.1 x 2.5 [2.8 ; 2.9] 3.2 microns, Q = 1.9 [2.1 ; 2.2] 2.4; N = 47; C = 95%; Me = 6.1 x 2.8 microns; Qe = 2.2. Basidia dimensions approximately 20 x 4.5 microns.Olympus CH20, NEA 100x/1.25, magnification 1.000 x, oil, in water (spores) and NEA 40x/0.65, magnification 400x, in water, congo red (hymenium, cystidia). AmScope MA500 digital camera.

Herbarium: Mycotheca and lichen herbarium (LJU-Li) of Slovenian Forestry Institute, Večna pot 2, Ljubljana, Index Herbariorum LJF

Ref.:
(1) Personal communication with Mr. Bojam Rot, www.gobenabovskem.com
(2) A. Bernicchia, Polyporaceaes.l., Fungi Europaei, Vol. 10., Edizioni Candusso (2005), p 296.
(3) L. Ryvarden, R.L. Gilbertson, European Polypores, Fungiflora, Vol.1. (1993), p 352.
(4) G. J. Krieglsteiner (Hrsg.), Die Grosspilze Baden-Württembergs, Band 1, Ulmer (2000), p 329. (5) J. Breitenbach, F. Kraenzlin, Eds., Fungi of Switzerland, Vol.2. Verlag Mykologia (1984), p 176.
(6) http://www.messiah.edu/Oakes//fungi_on_wood/poroid%20fungi/species%20pages/Irpex%20lacteus.htm

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