The violet webcap, Cortinarius violaceus (L.) Gray.
Classification
Kingdom Fungi
Phylum Basidiomycota
Class Basidiomycetes
Order Agaricales
Family Cortinariaceae
Genus Cortinarius
Synonyms
Agaricus violaceus L.
Common names
Violet cort
Violet webcap
Dunkelvioletter Schleierling (German)
Description
Cap: 5-12 cm diameter, fleshy, rounded then flattened and bluntly umbonate, sometimes campanulate, dark violet, with rather wooly down becoming cracked into scales, margin at first incurved.
Stem: up to 10-12 cm long and 2.5 cm thick, dark violet color, thickened below into a bulb, fibrous and somewhat scaly with darker fibrils.
Gills: dark violet at first then flushed with the rust-brown spores, adnate then sometimes separating, broad, firm, rather distant and connected by veins. The gill edge consists of violet-colored, flask-shaped cystidia.
Flesh: bluish-violet or purple, darker in the stem, firm.
Spore print: rust-brown.
Odor: smells slightly of cedarwood; no distinguishing taste.
Spores: yellow-brown, elliptical or pip-shaped, warted, 12-14 x 7-8 µm.
Habitat: found on the ground in woods, especially under birch and pine. Autumn.
The rich color of the violet webcap is due to an ink which consists of Fe(III) ions and the amino acid β-dopa (Nussbaum et al., 1998).
Medicinal properties
Antitumor effects
Polysaccharides extracted from the mycelial culture of C. violaceus and administered intraperitoneally into white mice at a dosage of 300 mg/kg inhibited the growth of Sarcoma 180 and Ehrlich solid cancers by 100% and 90%, respectively (Ohtsuka et al., 1973).
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Links
Go here for an interesting discussion on the difficulties of positively identifying specimens with only the photograph and lacking proper field notes 
References
Nussbaum F, Spiteller P, Rueth M, Steglich, Wanner WB, Gamblin B, Stievano L, Wagner FE.
An iron(III)-catechol complex as a mushroom pigment.
Angew. Chem. Int. Ed. 1998 37(23):3292–5.
Abstract from Interscience
Ohtsuka S, Ueno S, Yoshikumi C, Hirose F, Ohmura Y, Wada T, Fujii T, Takahashi E.
Polysaccharides having an anticarcinogenic effect and a method of producing them from species of Basidiomycetes.
UK Patent 1331513, 26 September 1973.
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