What You Should Know
Macrocystidia cucumis is a common, inedible mushroom of the genus Macrocystidia, often found in large numbers on needle litter or moist soil. When fresh, it is a handsome mushroom, the cap translucent-striate, dark-brown to brownish-orange with a contrasting lighter margin. It soon fades, however, to an unattractive dingy-buff, but still can be recognized by a dark-brown, pruinose stipe and pinkish-brown spore print. Usually found in nutrient-rich soils among herbaceous plants in gardens and parks rather than in forests (although it can occur there, usually along trail sides).
The pinkish spores are suggestive of the family Entolomataceae, but members of this group have angular, not elliptical spores. It is sometimes confused with Flammulina velutipes another lignicolous species, but the latter lacks a cucumber odor and has white rather than pinkish-brown spores.
Other names: Cucumber Cap, Cucumber-scented Mushroom.
Macrocystidia cucumis Mushroom Identification
Saprobic; terrestrial; growing alone, gregariously or in troops in woods, disturbed ground, grassy areas, gardens, and so on; summer and fall (or winter in warm climates); fairly widely distributed in North America (documented in the Pacific Northwest, Illinois, Ohio, and Quebec) but seldom collected.
1-6 cm across; bell-shaped at first, becoming broadly bell-shaped, broadly convex, or nearly flat; smooth, silky, or very finely velvety; dark reddish-brown, often with a paler margin; fading with age.
Attached to the stem (sometimes by a notch); close; whitish, becoming yellowish to pinkish yellow.
Up to 8 cm long and 5 mm thick; more or less equal; dry; finely velvety; tough; colored like the cap, but paler above and darker below.
Odor and Taste
Odor strong, reminiscent of cucumbers or fish; taste mild or slightly fishy.
Variable; whitish, pinkish, dirty yellowish, pale pinkish brown.
KOH dark olive, then gray on cap surface.
Spores 7-9 x 3-4.5 µ; smooth; elliptical; inamyloid. Enormous, lanceolate cystidia (up to 90 µ long and over 20 µ wide) on cap surface, gills, and stem surface.
Macrocystidia cucumis Look-Alikes
More viscid and grows on rotten wood; its gills are much paler than those of Cucumber Cap, and the cap usually flattens, whereas caps of Macrocystidia cuccumis tend to remain bell-shaped much longer.
A winter-fruiting species that appear on trees; it also has a dark and velvety stem but the cap is orange and does not smell of cucumber; its spore print is white.
Macrocystidia cucumis Taxonomy and Etymology
This saprobic fungus was described in the scientific literature in 1796 by Christiaan Hendrik Persoon, who gave it the binomial name Agaricus cucumis.
In 1934 French mycologist Marcel Josserand (1900-1992) transferred this species to its current genus, thus establishing its currently-accepted scientific name Macrocystidia cucumis.
Synonyms of Macrocystidia cucumis include Agaricus cucumis Pers., Agaricus nigripes Trog, Agaricus pisciodorus Ces., Naucoria cucumis (Pers) P. Kumm., Agaricus piceus Kalchbr., Nolanea nigripes (Trog) Gillet, Nolanea picea (Kalchbr.) Gillet, Nolanea pisciodora (Ces.) Gillet, and Naucoria cucumis var. leucospora J. E. Lange
Macrocystidia, the genus name, means 'possessing very large cystidia'. Cystidia (singular cystidium) are large, (usually inflated) sterile cells that occur in between the spore-bearing basidia, and in mushrooms of this genus, they are very big indeed.
The specific epithet cucumis comes from Latin and simply means 'of cucumber'.
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