Material examined. - NEW ZEALAND: North Island, Prov. Wellington, Butterfly, 10 VII 1949, Stevenson 715 (Holotype, K).- South Island, Prov. Fjordland, Milford Sound, 1 IV 1969, Horak 69-200 (SFSU, ZT); Prov. Nelson, Whanganui Inlet, 16 V 1968, Horak 68463 (ZT).

Pileus 15-25(-40) mm diam, convex to obtusely convex-umbonate when young, expanding with age to plano-convex or plano-umbonate; disc radially wrinkled; margin non-striate, incurved and remaining so in age; surface dull, dry, conspicuously velutinous; evenly deep brown with sooty tones, dark chestnut, dark orangish brown or dark reddish brown. Texture membranaceous, tough; context white to cream.- Lamellae adnexed to adnate, close (27-32) with 1-2 series of lamellulae, broad (up to 3 mm), yellowish white to cream; edges fimbriate, reddish brown.- Stipe (20-)35-70 x 2-3(-4) mm, central, cylindrical, equal or gradually attenuated towards the apex, tough, hollow, dry, pruinose to minutely velutinous overall, non-insititious, base covered with dense, yellowish ochre mycelial strands or strigose hairs; apex cream to orange brown, grading to dark orangish brown to dark brown towards the base; context orangish brown.- Odor and taste unpleasant, weakly spermatic.
Basidiospores (9-)10-12 x 4.5-5.5 µm, ellipsoid to subfusoid, sometimes slightly curved in profile, smooth, thin-walled, hyaline, inamyloid. - Basidia 24-36 x 6-8 µm , cylindrical to subclavate, 4-spored, clamped. - Cheilocystidia common, of Siccus-type cells; main body 15-35 x 4-8 µm , cylindrical to subfusoid, moderately thick-walled (up to 0.5 µm), yellowish brown to brown; apical setulae 2-30 x 2-3 µm , cylindrical to needle-shaped, acute, thin-walled to thick-walled, hyaline to pale reddish brown.- Pleurocystidia and hymenial setae absent. - Pileipellis hymeniform, of Siccus-type cells; main body 15-35 x 5-10 µm, cylindrical to clavate or a irregular in outline, sometimes forked, thin-walled to thick-walled, yellowish brown to brown; apical setulae 5-25 x 1.0-2.5 µm, cylindrical to narrowly acute; or needle-shaped, thin-walled to thick-walled, brownish; pilosetae absent. - Pi1eus trama dextrinoid-. Lame11ar trama with oleiferous hyphae, weakly dextrinoid.- Stipe tissue monomitic; cortical hyphae cylindrical, thick-walled, orangish brown; medullary hyphae similar but thinner walled. - Cau1osetae common, 30-80 x 4-8 µm, fusoid, lanceolate or needle-shaped, sometimes branched, apex acute, firm-walled, orangish brown.- C1amp connections present.

Habit, habitat and distribution.- Solitary,onleaflitterofNothofagus solandri (Holotype), or on litter under Nothofagus fusca, N. menziesii, N. truncata (Fagaceae), Dacrydium cupressinum (Podocarpaceae), and Metrosideros umbellata (Myrtaceae). New Zealand.

Diagnostic features of M. atrocastaneus include: a convex-umbonate, non-striate, conspicuously velutinous, dark brown pileus; close, broad, cream-colored lamellae with reddish brown edges; a dark orangish brown to brown, velutinous, non-insititious stipe; pileipellis cells and cheilocystidia with very long, acute setulae; no pleurocystidia or hymenial setae; and abundant caulosetae. The presence of caulosetae and Siccus-type pileipellis elements indicate placement in sect. Sicci, series Atrorubentes. The New Zealand species appears most phenetically similar to M. umbrinus Pegler, described from east Africa. Marasmius umbrinus differs in forming longer and narrower basidiospores (11.5-15.0 x 3.3-4.8 µm), and Siccus-type caulocystidia with 1-8 apical setulae (fide Pegler, 1977).

[Notes from Kew Type specimen, PRJ 2010] Other collections at K Stevenson GS 1183

Pileus 1.5-4 cm diam., dark chestnut, intensely velvety, plano-convex with down-rolled margin, becoming plane; flesh tough, creamy yellow. Gills adnate, seceding, creamy yellow, moderately crowded. Stipe 2-4 cm x 3-4 mm, yellowish immediately beneath gills, then brownish orange to dark chestnut, velvety, tough, hollow. Spores 11-12 x 6 µm, non-amyloid, hyaline. Cuticle of pseudo-amyloid broom-cells with strongly pigmented fringes. Strong unpleasant smell.

Bound with white mycelium to clumps of Nothofagus solandri litter, Butterfly, Wellington, 10.7.1949, Stevenson (type); Roding Valley, Nelson, 20.4.1957, E. B. Kidson.

Pileus 1.5-4 µm diam., fusco-castaneus, intense velutinus, plano-convexus, margine deorsum revoluto, usque planus; came tenaci cremeo-lutea. Lamellae adnatae, secedentes, cremeo-luteae, modice confertae. Stipes 2-4 cm x 2-4 mm, sub ipsas lamellas lutescens, inferne brunneo-aurantiacus usque fusco-castaneus, velutinus, tenax, cavus. Sporae 11-12 x 6 µm, haud amyloideae, hyalinae. Cuticula e cellulis scopiformibus pseudo-amyloideis laciniis intense coloratis sistens. Odor fortis, ingratus.

Typus: Stevenson 715.