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The Genus Lactarius

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Willamette Valley Mushroom Society Study Group Presentation

March 2022

Zhenia Ball

Richard Iltis

Margaret Spahn

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Presentation Outline:

  • Taxonomy
  • Field Markers of the Genus Lactarius
  • Unique Anatomical Features in Lactarius
  • Ectomycorrhizal Relationships
  • Sampling of Lactarius species found in Oregon
  • Field Identification of Two Species
    • Lactarius rubidus
    • Lactarius rubrilactious

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Lactarius Taxonomy

Kingdom (Kathy) Fungi

powdery mildew, black mold, athlete’s foot, mushrooms, …….

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Division (Does) Eumycota

true fungi, commonly body is mycelium

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Subdivision (Special) Basidiomycotina (Basidiomycota)

spores produced outside body on basidiums (basidia)

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Class (Candy) Hymenomycetes [Gastromycetes—puff balls, earth stars, ..] (Agaricomycetes?)

“looks like a mushroom”

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Order (On) Agaricales (Russulales)

gilled mushrooms

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Family (Friday) Russulaceae (genera include Lactarius, Russala, Lactifluus, ..)

brittle bodies

Genus (Great) Lactarius (Milk Caps)

no veil, ring, or volva; brittle, stalk snaps open cleanly like a piece of chalk; spores white, yellow, or ochre

a cut near stalk on gills produces latex on young mushrooms (sometimes)

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Species (Stuff) rubrilacteus, deliciosus, rubidus, ….

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How to differentiate Lactarius and Russula when there is no latex

(both have brittle bodies, only Lactarius has latex sometimes)

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Body has greenish stains, then likely L.

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Cap brightly colored and white flesh, then likely R.

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Cap margins striate, then likely R.

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Gills, stalk, or flesh not white or yellow when fresh, then likely L.

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Stalk pitted with darker spots, then likely L.

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None of the above, then try R. first and L. second.

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(See Arora MD, p. 63)

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Why are Lactarius species brittle?

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Lactarius mushrooms contain rounded cells called sphaerocysts, rather than elongated hyphae. The concentration and distribution of sphaerocysts within the fruiting body varies among Lactarius (and Russala) species.

Source: https://www2.muse.it/russulales-news/in_characteristics.asp

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The latex of milky caps contain compounds that are insoluble in water. Some constituents of Lactarius latex:

  • Fatty acids, amino acids
  • Sugars
  • Phenolic compounds
  • Organic acids
  • Tocopherols
  • Some compounds with high antioxidant activity and potential medicinal value
  • Some compounds with toxic and mutagenic activity

https://ejons.co.uk/Makaleler/1828111020_%c4%b0lk%20sayfa%208-5.pdfhttps://www.ncbi.nlm.nih.gov/pmc/articles/PMC6271741/

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Lactarius species contain extensively branched networks of lactifers – specialized cells containing the “latex”. Russalas also have lactifers, primarily in the cap and gill trama, but they are not so branched, get smaller near the mushroom surfaces, and do not exude latex when damaged.

Lactarius Contain Latex and Lactifers:

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Lactarius form Ectomycorrhizal Associations

Nutrients move from the fungus to the plant, and to different plants in the community through extended fungal networks. The plant benefits from increased water and mineral transport through the ectomycorrhizae. The fungus, in turn, has a reliable source of carbohydrates supplied by the tree.

All Lactarius species are ectomycorrhizal. They form symbiotic or mutualistic associations with plant roots.

Individual species are associated with particular species or families of trees. The Lactarius cannot develop without the presence of its plant partner.

A tree, however, might have multiple ectomycorrhizal partners.

Source: http://www.fungikingdom.net/

Ectomycorrhizae are the symbiotic structures that associate with the plant roots. Ectomycorrhizae remain external to the root, in contrast to endomycorrhizae, which colonize the root cells of the plant internally.

Source: https://www2.muse.it/russulales-news/in_characteristics.asp

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Lactarius Species in Oregon

25 species with “research grade” iNaturalist observations in Oregon - all observations were west of Bend

Douglas Fir

Wide Range of Forest Types Maple, Oak, DF and other Conifers

Pine

Conifers, esp. Sitka Spruce

Mixed forests, esp. D Fir and Live Oak

Tree associations identified in Siegel and Schwartz or Aurora

Conifers, esp. W. Hemlock and Grand Fir

Conifers, esp. Sitka Spruce

Mixed forest, but esp. W. Hemlock

Pine

Introduced Birch

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Conifers, esp. Sitka Spruce

Conifers, esp. Sitka Spruce

Western Hemlock and Grand Fir

Sitka Spruce

Mixed Madrone, Tanoak, D.Fir

Aspens and Cottonwoods

Sitka Spruce

Coast Live Oak

Alder

Alder and Conifers

Conifers

Pine, Spruce, Conifers

Conifers, esp Spruce and Fir

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Candy Cap (Lactarius Rubidus, Fragilis)

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Key features:

  • Cap and stalk burnt orange to orange-brown
  • Cap small, surface dull and dry, never sticky, slimy or shiny
  • Fresh gills exude a watery white latex
  • Dry/older gills lack milk but have maple syrup aroma
  • Neither milk nor flesh change color after exposure
  • Entire mushroom brittle
  • Veil, ring or volva absent
  • Odor sweet when cooked or dried
  • Taste not peppery
  • Spores white
  • Mature cap bald, flat to slightly sunken or with a small central knob
  • Cap feels nubby, not smooth

Habitat

  • On ground or rotten wood in forests, usually in groups
  • Pacific NW to California
  • Late fall through early spring
  • Both under pine and live oak, Rufulus exclusively under oak

Edibility

  • Delicious fresh but sweeter dried
  • Excellent in cookies, breads, waffles, and pancakes

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Bleeding Milk Cap (Lactarius rubrilacteus)

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Key features:

  • Cap bald, reddish-brown to orangish to tan, with darker and lighter concentric zones, often with greenish stains
  • Gills reddish, purplish-red or tan, broadly attached to stalk or running down it
  • Stalk colored more or less like cap
  • Entire mushroom brittle
  • Flesh exuding a dark red juice when cut, or at least showing traces of dark red color.
  • Bruised areas staining green within several hours
  • Veil, ring, and volva absent
  • Taste not peppery
  • Often confused with Lactarius deliciosus, but the gills and juice are redder.

Habitat

  • On ground or under conifers (mainly Douglas-fir)
  • Common on the west coast
  • Abundant in the fall and early winter

Edibility

  • Tastes fairly good, better than Lactarius deliciosus
  • Commonly salted or pickled

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Useful References:

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  • Online Key to NW Lactarius: https://www.svims.ca/council/Lactar.htm

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  • Online key to 75+ North American species of Lactarius
  • http://www.mushroomexpert.com/lactarius.html

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Thank you!