What You Should Know
Marasmius rotula is a common species of agaric fungus in the family Marasmiaceae. It is found in hardwood forests from spring to fall, growing from sticks and other woody debris. That last detail is very important because Marasmius capillaris, which looks nearly identical, grows from leaf litter rather than wood. Cap is whitish.
The attachment of the gills is using a tiny "collar" that circles the stem. Additional distinctive features include the dark, wiry stem; the pleated white cap that looks squarish when viewed from the side (the cap of Marasmius capillaris, in contrast, is usually more rounded); and the absence of a distinctive odor or taste.
Unlike other mushrooms known to release spores in response to a circadian rhythm, spore release in M. rotula is dependent upon sufficient moisture. Dried mushrooms may revive after rehydrating and continue to release spores for up to three weeks — a sustained spore production of markedly longer duration than other typical agarics.
Marasmius rotula is generally considered inedible but is not poisonous.
Other names: Pinwheel Mushroom, Pinwheel Marasmius, Little Wheel, Collared Parachute, Horse Hair Fungus.
Marasmius rotula Mushroom Identification
Saprobic on sticks and woody debris in hardwood forests; growing alone or gregariously (or in clusters); spring through fall; widely distributed east of the Rocky Mountains.
5-20 mm; broadly convex; soon developing a navel-like central depression; pleated; usually appearing to have a flat top and squarish sides when viewed from the side; bald; dry; brownish in the depression, white elsewhere.
Attached to a tiny "collar" that encircles the stem; white to yellowish-white; distant.
1.5-8 cm long; 1-2 mm thick; equal; dry; shiny; wiry; pale at first but soon dark brown to black except at the apex; base sometimes with stiff hairs.
Odor and Taste
KOH on cap surface negative.
White or whitish.
Spores 6.5-10 x 3-5 µ; smooth; more or less elliptical, or subfusiform; inamyloid. Pleurocystidia absent. Cheilocystidia clavate to subglobose; inamyloid; with short warts and projections. Pileipellis hymeniform, with broom cells that feature short projections.
A similar species Gymnopus androsaceus, known as the Horsehair Parachute, has its gills attached to the stem rather than to a collar.
Marasmius rotula Taxonomy and Etymology
This mushroom was described in 1772 by Italian mycologist Giovanni Antonio Scopoli, who named it Agaricus rotula. The Collared Parachute was redescribed by the great Swedish mycologist Elias Magnus Fries in his Systema Mycologicum of 1821. Seventeen years later, in his Epicrisis Systematis Mycologici (1838) Fries transferred this little mushroom to the Marasmius genus
Despite its diminutive size, Marasmius rotula was selected by Fries as the type species of the Marasmius genus, which shares some much larger agarics such as Marasmius oreades.
Synonyms of Marasmius rotula include Agaricus rotula Scop., Merulius collariatus With., Micromphale collariatum (With.) Gray, Androsaceus rotula (Scop.) Pat., and Chamaeceras rotula (Scop.) Kuntze.
The genus name Marasmius comes from the Greek word marasmos, meaning 'drying out'. Elias Magnus Fries, who separated the Marasmius genus from the similar white-spored Collybia fungi, used as a key differentiating factor the ability of Marasmius mushrooms to recover if rehydrated after drying out. Fries called this drought survival characteristic 'marescence'.
The reason for the specific epithet rotula becomes obvious when you turn over a cap and see that the inner collar, the gills, and the outer rim of the cap look so much like the hub, spokes, and rim of a wheel: "rot" (as in rotula) is a reference to a wheel, as it is also in the verb "rotate".
Marasmius rotula Uses
Louis Krieger, writing in National Geographic in the 1920s, noted that the mushroom was used as an addition to gravies and when used to garnish venison, "adds the appropriate touch of the wild woodlands." The fruit bodies will bioaccumulate cadmium: a study of the metal concentration of 15 wild mushroom species of India showed that M. rotula accumulated the highest concentration of that metal.
A peroxidase enzyme known as MroAPO (Marasmius rotula aromatic peroxygenase) is attracting research interest for possible applications in biocatalysis. In general, enzymes that catalyze oxygen-transfer reactions are of great utility in chemical synthesis since they work selectively and under ambient conditions. Fungal peroxidases can catalyze oxidations that are difficult for the organic chemist, including those involving aromatic substrates such as aniline, 4-aminophenol, hydroquinone, resorcinol, catechol, and paracetamol.
The M. rotula enzyme is the first fungal peroxygenase that can be produced in high yields. It is highly stable over a wide pH range, and in a variety of organic solvents. The enzyme has another potential for use as a biosensor for aromatic substances in environmental analysis and drug monitoring.
Photo 1 - Author: Jerzy Opioła (Creative Commons Attribution-Share Alike 4.0 International)
Photo 2 - Author: Eric Smith (Bobzimmer) (Creative Commons Attribution-Share Alike 3.0 Unported)
Photo 3 - Author: spacecowboy (Creative Commons Attribution 4.0 International)
Photo 4 - Author: mangoblatt (Public Domain)