What You Should Know
Phyllotopsis nidulans is a species of fungus in the family Tricholomataceae, and the type species of the genus Phyllotopsis. The fungus fruit body consists of a fan-shaped, light orange fuzzy cap up to 8 cm (3 in) wide that grows singly or in overlapping clusters. On the cap, underside are crowded orange gills. It has a strong, unpleasant odor. It is inedible though nonpoisonous.
This mushroom is widely distributed in temperate regions of the Northern Hemisphere. Its range extends north to Alaska and includes Costa Rica, where it has been recorded in the Talamanca mountains and on the Poas Volcano. In Asia, it has been recorded in Korea.
Mycology is still working on the question of where, precisely, to place Phyllotopsis nidulans in the fungal world. It has traditionally been placed in the Tricholomataceae, but DNA studies have not supported this idea. Most recently, Lodge and collaborators (2013) have informally placed Phyllotopsis nidulans in what they call "the basal Hygrophoroid clade," closely related to but separate from the hygrophoroid mushrooms, clustered with species of Tricholomopsis, Pleurocybella porrigens, and others.
Other names: The Mock Oyster, The Orange Oyster.
Phyllotopsis nidulans Mushroom Identification
Saprobic on the deadwood of hardwoods and conifers - often those fairly recently dead, with the bark still adnate; causing a white, stringy rot; growing gregariously or in overlapping clusters; fall and spring, or overwinter in warm climates; widely distributed in North America.
2–7 cm across at maturity; more or less fan-shaped or semicircular in outline; planoconvex; dry; prominently hairy, at least when young; sometimes with a whitish dusting at first, but soon bright orange, fading to yellowish-orange or orangish-yellow; the margin inrolled when young, and sometimes bruising brownish when handled.
Close or nearly crowded; thin; short-gills frequent; bright to pale orange.
Absent or very poorly developed and lateral. Caps sometimes appear to share a poorly defined "base." Occasionally gills develop on the substrate below the cap, appearing almost resupinate.
Pale orange; soft; not changing when sliced.
Odor and Taste
Taste mild or foul; odor strong and foul, reminiscent of skunk cabbage - or in some collections not distinctive.
KOH negative on cap surface, flesh, and gills.
Very pale pink (often appearing white unless viewed against a pure white background).
Spores 4.5–6 x 1.5–2.5 µm; allantoid; smooth; hyaline in KOH; inamyloid. Hymenial cystidia not found. Pileipellis a tangled cutis; elements about 2.5 µ wide, smooth, hyaline, clamped at septa; hairs composed of elements 5–10 µm wide, frequently septate, smooth, orangish in KOH, with cylindric to fusiform terminal cells.
Phyllotopsis subnidulans, found in the eastern US, are similar in appearance to P. nidulans. The former species can be distinguished by deeper orange color, thinner gills with wider inter-gill spacing, and curved to sausage-shaped spores. Other similar species include Lentinus strigosus, Panus conchatus, and Pleurotus ostreatus.
Phyllotopsis nidulans Taxonomy
The mock oyster was first described scientifically in 1798 by Christian Hendrik Persoon as Agaricus nidulans. The specific epithet nidulans means "partly encased or lying in a cavity". It is commonly known as "nestcap".
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