Gymnopus section Iocephalae Singer ex Halling, Mycotaxon 63: 363. 1997.
Sect. Iocephalae Singer ex Halling, Mycologia Mem. 8: 32. 1983.
Basidiomata marcescent, with violet to purple pigments, changing to blue in alkali and pale pink in acid.
Type species: Gymnopus iocephalus (Berk. & Curt.) Halling
Marasmius iocephalus (Berk. & Curt.) Pennington, N. Amer. Flora 9: 271. 1915.
Collybia iocephala (Berk. & Curt.) Singer, Lloydia 9: 116. 1949.
Spore deposit almost pure white (Singer 1946). Spores 6.5-8.6 x 3.2-4.4 µm, lacrymoid in profile, ovoid in face or back view, smooth, inamyloid, acyanophilous. Basidia 16.2-27 x 4.2-6.5 µm, four sterigmate, cylindric to clavate, not siderophilous. Pleurocystidia and cheilocystidia absent. Some pinkish violet pigment interspersed among hymenial elements when mounted in water. Lamellar trama interwoven, inamyloid, with scattered interhyphal pigment deposits; cells 4.2-7.5 µm in diam. Pileus trama interwoven, inamyloid; hyphae 4.2-10.8 µm in diam. Pileipellis a layer of repent, cylindric, branched, interwoven hyphae; cells 3.2-7.5 µm in diam, with pinkish violet content when mounted in water, blue in alkali, yellowish in Melzer's. Occasional interhyphal pigment deposits present. Stipitipellis a layer of vertically oriented and parallel hyphae, with similar content as the pileipellis, branching or ascending to form long, cylindric-contorted caulocystidia; hyphae 2.2-5.4 µm in diam. Clamp connections present in all tissues. Macrochemical reactions: KOH--bright blue (tyrian blue) on the pileus, lamellae, and stipe.
Habit, habitat, and distribution: Scattered, gregarious to subcespitose on leaf litter and humus. Known from Florida west to Louisiana and north to Massachusetts.
Discussion: This species is unique in the genus because of the violet colors in the pileus, lamellae, and stipe. These colors in the stipe can be overlooked though, if the pubescence is well developed and extends over the length of the stipe. Singer (1946) said that the pigment is dissolved in the cell sap, but when tissues are mounted in Melzer's, the walls of the hyphae are purple. When mounted in water, scattered, amorphous, interhyphal deposits of pigment can be observed, and entire cells appear to be colored a violet pink. It would seem that the pigment involved is not encrusting, as in certain members of the Levipedes and Vestipedes, but the exact nature and location is still questionable.
In the original description, Berkeley and Curtis (1853) indicated that the odor of G. iocephalus was strong and offensive. Singer (1946) said this species has a disagreeable odor like sauerkraut. Collections from Florida were reported as smelling like gunpowder. Massachusetts material was said to have a garliclike or radishlike odor. In my own material from Florida, I could detect a gunpowder component, but also an alliaceous to fetid ingredient. Whether or not the odor is truly variable or merely perceived differently by individuals remains to be resolved.