Summary:
Features include 1) a slimy-viscid cinnamon tan cap, at first with a downy margin, 2) white milk whose droplets dry olive-cream, 3) pale cinnamon to pale tan gills, 4) a slimy stem colored as the gills near maturity, 5) a slight peppery taste, 6) a cream colored spore deposit, and 7) microscopic characters including amyloid ornamentation forming a sparse broken reticulum and some isolated warts. The description is derived from Hesler(4). Lactarius trivialis has been used as a name for Lactarius argillaceifolius var. megacarpus and for Lactarius kauffmanii var. kauffmanii at least in California (Methven). Lactarius trivialis is "common in northern Idaho in the fall and occurring generally in the conifer forests of the Pacific Northwest", (Hesler(4)).

Cap:
5-18cm across, convex, margin incurved, expanding to flat-convex then centrally depressed with uplifted margins; violaceous-fuscous in button stage ("benzo-brown"), but cinnamon-tan tones soon evident and at maturity cinnamon-tan ("cinnamon" to "Sayal-brown"), azonate to obscurely zonate; slimy viscid, bald, margin downy, soon smooth

Flesh:
thick, firm; whitish, MILK milk-white, droplets drying olive-buff, gills rarely stain olive-brown and then only slightly

Gills:
adnate, close (subdistant when old), broad, thin; gradually pale cinnamon to pale tan (darker)

Stem:
5-10(15)cm or more long, 1-2.5cm wide, more or less equal, fragile, hollow; colored as gills near maturity; slimy, soon dry, base at times white-strigose

Odor:
slight

Taste:
slowly slightly peppery

Microscopic spores:
spores from deposit 7.5-9(10) x 6-7.5(8) microns, broadly elliptic, [presumably amyloid] "ornamentation a sparse broken reticulum and some isolated warts", the bands narrow and the meshes far apart, prominences 0.2-0.4 microns high; basidia 4-spored, 45-52 x 10-12 microns; pleurocystidia: macrocystidia 75-100 x 7.5-13 microns, "fusoid to fusoid-ventricose, acuminate, content spangled as revived, some originating in subhymenium", pseudocystidia filamentous and crooked; cheilocystidia 45-67 x 4.5-9 microns, "subcylindric to fusoid and obtuse or acuminate"; cap cuticle "an ixolattice or an ixotrichoderm of septate hyphae, the slime KOH-soluble", the layer about 75 microns thick, slime persistent in Melzer''s reagent

Spore deposit:
cream color (pale dull yellow)

Notes:
Material was cited from WA, ID, AK, and Switzerland, (Hesler(4)). There is a collection from BC at the Pacific Forestry Centre and the University of British Columbia. The University of Washington has collections from AK, WA, MI, VT, Finland, and Sweden. DNA from what is regarded as Lactarius trivialis has been found in BC (D. Miller, pers. comm.).

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