Pi1eus 5-25 mm diam, hemispherical to convex when young, expanding in age to planoconvex with a depressed to subumbilicate or rarely obtusely umbonate disc; margin striate to subplicate, decurved, sometimes uplifted in age; surface dull, dry, minutely velutinous to granular-micaceous; disc umber brown with a reddish brown tone, paler towards the margin. Texture membranaceous, cartilaginous-tough; context thin.- Lamellae broadly adnate to subemarginate, subdistant (16-18) with 2 series of lamellulae, often anastomosing, broad (1.0-2.5 mm), whitish to pale beige; edges even to subfimbriate, concolorous.Stipe10-30(-35) x 1.0-1.5 mm, central, cylindrical, equal or gradually tapering towards the base, dull, dry, fistulose, tough-cartilaginous, pruinose to coarsely floccose overall; apex pale brown, base dark brown; rhizomorphs absent.- Odor and taste not distinctive.
Basidiospores 7-9(-11) x (3.0-)3.5-4.5 µm, narrowly ellipsoid to subcylindrical, smooth, thin-walled, hyaline, inamyloid.- Basidia 30-40 x (4)5-7 µm , cylindrical to subclavate, 4-spored, clamped.- Cheilocystidia abundant, 20-40 x 5-14 µm, polymorphic, cylindrical, clavate or irregular in outline, hyaline, thin-walled, with scattered apical to subapical diverticula 3-12 x 2-4 µm, knob-like or irregular in outline, sometimes lobed, hyaline.Pleurocystidia absent.- Pileipellis aRameales-structure with suberect to erect terminal cells, 20-50 x 5-15 µm, clavate or irregular in outline, often lobed, smooth or with scattered diverticula, brown-incrusted, weakly to strongly dextrinoid; diverticula 3-10 x 2-5 µm, knob-like to irregular in outline, obtuse, often forked, brown.- Pileal and 1amellar trama weakly dextrinoid, non-gelatinous.- Stipe t issue monomitic, strongly dextrinoid.- Cau1ocystidia numerous, 25-80 x 5-12 µm , polymorphic, similar to terminal cells of pileipellis, cylindrical to irregular in outline, with or without knob-like diverticula, thin-walled to moderately thick-walled, pale yellowish brown, dextrinoid or inamyloid.- Clamp connections present.

Habit, habitat and distribution.- Solitary, in groups on rotting needles and twigs of Dacrydium cupressinum (Podocarpaceae), rarely also on leaves of Weinmannia racemosa (Cunoniaceae). New Zealand.

Pileus 5-25 mm, convexus, aetate planus vel subumbonatus, striatus vel subplicatus, minute velutinus vel micaceus, umbrinus castaneo tinctu. Lamellae late adnatae vel subemarginatae, subdistantes, albidae vel pallide argillaceae. Stipes 10-30 x 1.0-1.5 mm, centralis, cylindricus, pruinosus vel floccosus, apicaliter pallide brunneus sursum fuscus, rhizomorpha nulla. Odor saporque nulli. Basidiosporae 7-9 x 3.5-4.5 µm , ellipsoideae vel subcylindraceae, leves, hyalinae, inamyloideae. Basidia 30-40 x 5-7 µm, 4-spora. Cheilocystidia 20-40 x 514 µm, cylindrica vel irregulariter clavata, diverticulis apicalibus, 3-12 x 2-4 µm, instructa. Pleurocystidia nulla. Pileipellis typi Ramealium, ex cellulis clavatis vel irregularibus, 20-50 x 5-15 µm, diverticulis irregularibus, 3-10 x 2-5 µm, instructis. Trama pilei vel lamellarum dextrinoideum, haud gelatinosum. Hyphae stipitis corticales conspicue dextrinoideae. Caulocystidia 25-80 x 5-12 µm, cylindrica vel irregularia, membrana tenuitunicata vel subcrassa, pallide luteobrunnea, dextrinoidea vel inamyloidea instructa. Fibulae praesentes. Solitarius, ad aciculas putridas Dacrydii cupressini vel rariter Weinmanniae racemosae. Nova Zelandia. Horak 68-142 (Holotypus, PDD).

Diagnostic features of M. rimuphilus include: a relatively large, umber brown, subplicate pileus; subdistant, white, non-marginate lamellae; a pruinose to floccose, dark brown, insititious stipe lacking rhizomorphs; pileipellis composed of a well-developed Rameales-structure; dextrinoid tissues; diverticulate cheilocystidia and caulocystidia; and growth on debris of rimu (Dacrydium cupressinum). Marasmius rimuphilus may be the taxon reported by Colenso (1886) as M. androsaceus (L. : Fr.) Fr., a common temperate Northern Hemisphere species. Marasmius androsaceus differs, however, in forming a glabrous stipe lacking conspicuous diverticulate caulocystidia, forms numerous black rhizomorphs and fewer lamellae (8-17). Other taxa with darkly pigmented pileus and pruinose stipe include M. hakgalensis Petch from Sri Lanka, South America and Zaire (Isotype, FH!), M. thiersii Desjardin from western North America (Holotype, SFSU!), and M. cryptotrichus Singer from Mexico (Holotype, F!). All of the latter taxa differ from M. rimuphilus in forming fewer lamellae, black rhizommophs, and cylindrical, non-diverticulate, thick-walled and longer caulocystidia.

Material examined. - NEW ZEALAND: South Island, Prov. Westland, Kopara, Nelson Creek, 23 III 1983, Horak 2077 (SFSU, ZT); Prov. Westland, S of Lake Hochstetter, 12 III 1968, Horak 68-142 (Holotype, PDD; Isotype, ZT).- Stewart Island, Ulva Island, 23 III 1969, Horak 69-160 (ZT).