Lactarius repraesentaneus

What You Should Know

Lactarius repraesentaneus is a species of fungus in the family Russulaceae. Distinguishing features of its fruit body include the large orange-yellow cap up to 18 cm (7.1 in) wide, cream to pale yellow gills, and a yellow coarsely-pitted stem that is up to 12 cm (4.7 in) long and 3 cm (1.2 in) thick. Cut fruit bodies ooze a white latex that will stain mushroom tissue lilac to purple. It has a northerly distribution and is found in temperate regions of North America and Europe, associated with spruce trees. When fresh it has a distinctive, fragrant odor.

Although it is unlikely to cause death or long-term illness, this is a poisonous mushroom. Yellow Bearded Milkcaps are rare and so should not be collected except for essential scientific study. These toxic toadstools should not be gathered for eating because they can cause unpleasant stomach pains, sickness, and a burning sensation in the throat.

Other names: Yellow Bearded Milkcap, Northern Bearded Milkcap, The Northern Milkcap, The Purple-Staining Milkcap.

Lactarius repraesentaneus Mushroom Identification

1. Ecology

   Mycorrhizal with spruces (in the southern Rocky Mountains it is fond of Engelmann spruce); summer and fall; widely distributed in northern and montane North America.

2. Cap

   4–14 cm; convex with an incurved margin when young; becoming flat, shallowly depressed, or shallowly vase-shaped; slimy when fresh; hairy—especially at the margin, which is "bearded" when the mushroom is young; pale to dark yellow or orangish-yellow; usually without concentric zones of color; often bruising lilac to purple when handled.

3. Gills

   Attached to the stem or beginning to run down it; close; short-gills frequent; sometimes forked near the stem; whitish at first, becoming yellowish or orangish; stained lilac to purple by the milk where damaged.

4. Stem

   3–8 cm long; up to 3 cm thick; more or less equal, or slightly club-shaped; slimy when fresh; usually featuring potholes; whitish or pale yellowish; bruising and discoloring lilac to purple; becoming hollow; basal mycelium white.

5. Flesh

   White; changing to lilac when sliced.

6. Milk

   White; copious; staining tissues lilac to purple.

7. Odor and Taste

   Odor fragrant or not distinctive; taste usually bitter to acrid, but sometimes mild.

8. Chemical Reactions

   KOH red on cap surface.

9. Spore Print

   Creamy or yellowish.

10. Microscopic Features

    Spores 6.5–8 x 5.5–7 µm in the collection I have studied, but usually reported as somewhat larger (9–11 µm long); broadly ellipsoid to nearly subglobose; ornamentation as amyloid spines and connecting lines up to 0.5 µm high, often forming striped patterns and partial reticula (and sometimes nearly completely, though widely, reticulate). Hymenial cystidia fusiform, with long tapering necks that feature several apical constrictions; to about 90 x 10 µm. Pileipellis an ixocutis of elements 2.5–5 µm wide, golden in KOH.

Lactarius repraesentaneus Look-Alikes

1. Lactarius scrobiculatus

   Produces latex that does not turn lilac but turns yellow, its spores are smaller. This very rare milkcap has not been recorded in Britain for many years.

2. Lactarius torminosus

   Has a pale pink to pinkish-orange woolly cap and grows under birches usually in damp soil.

3. Lactarius pubescens

   Has a buff-white or cream woolly cap and grows mainly in damp grass under birch trees.

4. Lactarius uvidus

   Has a violet reaction but it has a different color and is not hairy at the margin of the cap.

5. Lactarius flavidus

   Has a yellowish cap but does not have a hairy margin.

Lactarius repraesentaneus Taxonomy and Etymology

Lactarius repraesentaneus was first described by German mycologist Max Britzelmayr in 1885, based on material collected from Bavaria. The variety Lactarius scrobiculatus var. repraesentaneus, proposed by Killermann in 1933, is considered a synonym. Rolf Singer in 1942 defined the subspecies L. repraesentaneus ssp. speciosus to include fruit bodies with matted fibers ("felt") arranged in concentric rings on the cap (zonate), in comparison with the nominate subspecies, where in young specimens the felt was evenly distributed on the cap surface, only becoming zonate at the cap margins in maturity.

According to the classification proposed by Lexemuel Ray Hesler and Alexander H. Smith in their 1979 monograph of North American Lactarius species, L. repraesentaneus belongs in the stirps Speciosus of the section Aspideini, of the subgenus Piperites of genus Lactarius. Other species in stirps Speciosus include L. dispersus, L. subtorminosus, and L. speciosus, all of which have a hairy cap edge. Singer's 1986 classification of the Agaricales does not divide subsection Aspideini into stirpes, instead grouping Lactarius repraesentaneus with L. aspideus, L. uvidus, L. luridis, L. psammicola, and L. speciosus.

The specific epithet repraesentaneus is Latin for "well-represented".

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.

Sources:

Photo 1 - Author: Irene Andersson (irenea) (Creative Commons Attribution-Share Alike 3.0 Unported)

Photo 2 - Author: (Photo by E. Barge) Barge EG, Cripps CL (2016) New reports, phylogenetic analysis, and a key to Lactarius Pers. in the Greater Yellowstone Ecosystem informed by molecular data. MycoKeys 15: 1-58. https://doi.org/10.3897/mycokeys.15.9587 (Creative Commons Attribution 4.0 International)

Photo 3 - Author: natureluvr01 (Creative Commons Attribution 2.0 Generic)

Photo 4 - Author: 2012-03-22_Lactarius_repraesentaneus_Britzelm_207231.jpg: (Creative Commons Attribution-Share Alike 3.0 Unported)