Lactarius tabidus Fr. - Birch Milkcap

Phylum: Basidiomycota - Class: Agaricomycetes - Order: Russulales - Family: Russulaceae

Distribution - Taxonomic History- Etymology - Identification - Culinary Notes - Reference Sources

Lactarius tabidus, the Birch Milkcap, is found in great abundance beneath birch trees in areas where the soil is damp, humus-rich and mossy. The white milk (latex) is sometimes rather sparse, especially in very young or old specimens and during prolonged dry weather.

Taste testing is an important step in identifying milkcap mushrooms, but for red-brown such as this it's best to taste only a little piece because some of its lookalikes produce extremely hot latex.

Distribution

Widespread and very common throughout Britain and Ireland, the Birch Milkcap is also found in most parts of mainland Europe. A very similar milkcap occurs in North America, reportedly mycorrhizal with pines; maybe one day DNA sequencing will show whether it is co-specific with the European species Lactarius tabidus.

Taxonomic history

The Birch Milkcap was described in 1838 by the Swedish mycologist Elias Magnus Fries, who established its scientific name as Lactarius rufus, which is still the binomial name by which it is generally referred to by mycologists today.

Synonyms of Lactarius tabidus include Lactarius subdulcis var. tabidus (Fr.) Quél., and Lactarius theiogalus.

Etymology

The generic name Lactarius means producing milk (lactating) - a reference to the milky latex that is exuded from the gills of milkcap fungi when they are cut or torn. The specific epithet tabidus is a Latin adjective that translates as 'stunted' - a reference to the small size of these milkcaps in comparison with many other members of the Lactarius genus.

Identification Guide

	Cap Convex at first, then flattening or becoming slightly funnel shaped, often with a shallow, narrow umbo; 2 to 4.5cm in diameter, the yellowish-brown to orange-brown caps, darkest towards the centre, are slightly hygrophanous and turn more ochre from the margin when old and dry. Caps have finely matt and wrinkled surfaces, and old specimens are often visibly crenulate at the margin.
	Gills The gills, which are pale cinnamon with a pinkish tinge, are weakly decurrent and crowded. As they mature, the gills tend to become blotchy. When the gills of this milkcap are damaged, a white latex is released; its taste is initially mild but later becomes acrid. On a white handkerchief or tissue the latex leaves a damp mark that slowly turns yellow. Stem Solid at first, eventually becoming hollow; 5 to 10mm in diameter and 3 to 7cm tall, the cylindrical or slightly upward-tapering stem is rather brittle; its surface is smooth and much the same colour as the cap, a little paler towards the apex and darker towards the base. The stem flesh is whitish; there is no stem ring.
	Spores Broadly ellipsoidal, 7-9 x 6-7μm, hyaline; ornamented with many pointed warts up to 1.2μm in height, mostly isolated but with just a few linking ridges. Show larger image Spores of Lactarius tabidus, Birch Milkcap  X  Spore print Pale cream with a slight salmon pink tinge.
Odour/taste	No distinctive odour; initially a mild taste that gradually becomes more acrid.
Habitat & Ecological role	Ectomycorrhizal with hardwood trees, notably birches; in damp and often mossy woodlands.
Season	August to November in Britain and Ireland.
Similar species	Lactarius subdulcis is of similar coloration; it occurs mostly under beech trees.

Culinary Notes

The Birch Milkcap is generally considered to be inedible because of its acrid taste.

Reference Sources

Fascinated by Fungi, 2nd Edition, Pat O'Reilly 2016, reprinted by Coch-y-bonddu Books in 2022.

Funga Nordica, Henning Knudsen and Jan Vesterholt, 2008.

Fungi of Switzerland, volume 6: Russulaceae, Kränzlin, F.

BMS List of 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.

Acknowledgements

This page includes pictures kindly contributed by David Kelly.

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