Pileus 2-3 mm diam, hemispherical to convex, disc not depressed, papilla absent, margin plicate and scalloped; surface dull, dry, glabrous; evenly dark brown to dark reddish brown. Texture membranaceous; context thin, concolorous with pileus surface.- Lamellae adnexed to almost free, subdistant (610), lamellulae absent, ventricose, off-white; edges even, concolorous.- Stipe10-25 x 0.2-0.4 mm, central, equal, wiry, tough, glabrous, polished, insititious; black overall; rhizomorphs absent.- Odor and tastenot distinctive.
Basidiospores 8.5-11.5 x 4-5 µm, ellipsoid, sometimes slightly curved in profile, smooth, thin-walled, hyaline, inamyloid.- Basidia 18-22 x 8-10 µm, clavate, 4-spored, clamped.- Cheilocystidiaof 2 types: a) scattered Rotalis-type cells 12-20 x 6-10 µm, broadly clavate, apically brown; divergent setulae 1-3 x 1 µm, cylindrical; b) 25-32 x 5-7 µm, fusoid to lanceolate, apex acute or subcapitate, hyaline, thin-walled.- Pleurocystidia absent. Pileipellis hymeniform, slightly mottled, composed of Rotalis-type cells; main body 12-20 x 7-15 µm, clavate, thick-walled, brown to reddish brown; divergent setulae 1-3 x 1 µm, cylindrical; on pileus disc thick-walled, clavate pileocystidia projecting beyond the Rotalis-type cells, 30-50 x 10-20 µm, covered with reddish brown, coarsely roughened, resinous incrustations.- Pileal and tramal tissue inamyloid.- Stipe tissue monomitic; cortical hyphae parallel, cylindrical, smooth or rougened.- Caulocystidia absent. Clamp connections present.

Habit, habitat and distribution.- Solitary, in groups on rotting leaves of Cordyline (Agavaceae). New Zealand.

Pileus 2-3 mm, hemisphaericus vel convexus, plicatus, glaber, fuscus vel castaneus. Lamellae adnexae vel subliberae, subdistantes, subalbidae. Stipes 10-25 x 0.2-0.4 mm, centralis, cylindricus, glaber, insititius, niger, rhizomorpha nulla. Odor saporque nulli. Basidiosporae 8.5-11.5 x 4-5 µm, ellipsoideae, leves, hyalinae, inamyloideae. Basidia 18-22 x 8-10 µm, 4spora. Cheilocystidia: a) typi Rotalis, 12-20 x 6-10 µm, late clavata, setulis cylindricis divergentibus, 1-3 x 1 µm, intructa; b) 25-32 x 5-7 µm, fusoidea vel lanceolata, apicaliter acuta vel subcapitata. Pleurocystidia nulla. Pileipellis hymeniformis typi Rotalis, ex cellulis clavatis 12-20 x 7-15 µm, setulis cylindraceis divergentibus, 1-3 x 1 µm, instructis, membrana crassa, brunnea vel castanea instructis. Pileocystidia typi Rotalis, 30-50 x 10-20 µm, clavata, materia castanea resinosa incrustata. Trama pilei et lamellarum inamyloideum. Hyphae stipitis corticales glabrae vel rugosae. Caulocystidia nulla. Fibulae praesentes. Solitarius, ad folia putrida Cordylinidis. Nova Zelandia. Horak 67-140 (Holotypus, PDD).

Diagnostic features of Marasmius exustoides include the following: small, convex, plicate, dark reddish brown pileus; non-collariate, non-marginate, subdistant, white lamellae; a relatively short, glabrous, insititious, black stipe; basidiospores 8.5-11.0 x 4-5 µm; two types of cheilocystidia; a pileus disc with clavate pileosclerocystidia covered with reddish brown, coarsely roughened, resinous incrustations; smooth to roughened but non-setulose stipe cortical hyphae; and growth on leaves of Cordyline. Marasmius exustoides is similar to M. exustus Berk. & M. A. Curtis, M. crescentiae Murrill, M. minutus Peck, and M. kroumirensis (Pat.) Sacc. & Sydow. Marasmius exustus, from the Bonin Islands, differs in forming much smaller basidiospores (6.5-8.0 x 4-5 µm), grows on dicotyledonous leaves, and lacks pileosclerocystidia on the pileus disc (Isotype, FH!). Marasmius crescentiae, from South America and Papua New Guinea, differs in forming paler and more yellowish brown pilei, smaller basidiospores (7.5-8.5 x 3.5-4.0 µm), has scattered pleurocystidia, densely setulose stipe cortical hyphae, and fusoid-lageniform pileoleptocystidia but no clavate pileosclerocystidia (Holotype, NY!). Marasmius minutus, from eastern North America and Europe, differs in forming smaller basidiospores 6.0-9.5 x 3-4 µm, numerous fusiform to lageniform pleurocystidia and pileoleptocystidia, setulose stipe cortical hyphae, and grows on dicotyledonous debris (Holotype, NYS!). Marasmius kroumirensis, from northern Africa, differs in forming only Rotalis-type cheilocystidia, and in having numerous fusiform to lanceolate pleurocystidia. Other micromorphological data of M. kroumirensis are unavailable because the species is known only from a single fragmented basidiome of the holotype specimen (fide Pegler, 1966).

Material examined -- NEW ZEALAND: South Island, Prov. Canterbury, Springfield, Mt. Grey, Kowai Bush, 28 IX 1967, Horak 67-140 (Holotype, PDD; Isotype, SFSU, ZT).