Pileus 3-10 mm diam, hemispherical when young, expanding in age to convex with a subdepressed disc, slightly plicate, tough, membranaceous; surface dull, dry, minutely pruinose overall (with hand lens); pale beige-brown.- Lamellae shallowly adnate to subfree, distant to remote (5-8), often fold-like, narrow, lamellulae absent; concolorous with pileus.- Stipe 8-18 x 0.2-0.3 mm, central, equal, cylindrical, wiry, minutely pruinose overall, insititious, erupting from black stroma-like spots up to 10 mm diam; apex white, black elsewhere.- Odor and taste not distinctive.
Basidiospores 9-11 x 4.5-5.5 µm, ellipsoid to broadly fusoid, smooth, thin-walled, hyaline, inamyloid.- Basidia 25-35 x 7-9 µm, clavate, 4-spored, clamped.- Cheilocystidia 40-55 x 5-11 µm, fusoid with elongated neck, hyaline, thin-walled.- Pleurocystidia absent.Pileipellis hymeniform, composed of Rotalis-type cells interspersed with a few non-setulose cells and numerous pileocystidia; Rotalis-type cells 15-24 x 10-20 µm, broadly clavate to subglobose, thin-walled, apically thick-walled, hyaline to pale yellow-brown; divergent setulae 1-2 x 1 µm, cylindrical.Pi1eocystidia 35-50 x 6-10 µm, fusiform or ventricose with long neck, hyaline, thin-walled; gloeocystidia absent.- Pileal and lamellar tissue inamyloid.- Stipe tissue monomitic; cortical hyphae parallel, cylindrical, roughened, dextrinoid.- Cau1ocystidia scattered, 25-45 x 5-9 µm, polymorphic, subacute, hyaline, thin-walled.- Clamp connections present.

Habit, habitat and distribution.- Solitary, on rotting palm, fronds of Rhopalostylis sapida (Palmae). New Zealand.

Pileus 3-10 mm, hemisphaericus dein subdepressoconvexus, subplicatus, minute pruinosus, pallide argillaceus. Lamellae adnatae vel subliberae, distantes, remotae, saepe plicatae, pileo concolores. Stipes 8-18 x 0.2-0.3 mm, centralis, cylindricus, minute pruinosus, insititius, apicaliter albus sursum niger. Odor saporque nulli. Basidiosporae 9-13 x 4.5-5.5 µm, ellipsoideae vel late fusoideae, leves, hyalinae, inamyloideae. Basidia 25-35 x 7-9 µm, 4-spora. Cheilocystidia 40-55 x 5-11 µm, fusoidea. Pleurocystidia nulla. Pileipellis hymeniformis, ex cellulis typi Rotalis, 15-24 x 10-20 µm, late clavatis vel subglobosis, setulis cylindraceis divergentibus, 1-2 x 1 µm, instructis. Pileocystidia 35-50 x 6-10 µm, fusiformia vel ventricosoelongata. Gloeocystidia nulla. Trama pilei et lamellarum inamyloideum. Hyphae stipitis corticales dextrinoideae. Caulocystidia 25-45 x 5-9 µm, polymorphica. Fibulae praesentes. Solitarius, ad folia Rhopalostylidis sapidae. Nova Zelandia. Horak 68-410 (Holotypus, PDD).

Marasmius rhopalostylidis forms small, beige pilei, well-developed distant lamellae, moderately large basidiospores, pileo-, cheilo-, and caulocystidia that are fusiform to ventricose with a long-tapered, non-capitate apex, and sporulates on rotting palm fronds of Rhopalostylis sapida. It differs from allied New Zealand taxa by the features presented in the key. It is similar to M. epiphylloides from Europe, and M. munyozii Singer from Chile. Marasmius epiphylloides differs in forming white pilei, poorly developed, intervenose lamellae, longer and narrower (11-17 x 2-4 µm), cylindrical basidiospores, and basidiome formation restricted to leaves and twigs of Hedera helix. Marasmius munyozii differs in forming more abundant lamellae (7-13), shorter and narrower basidiospores (6-8 x 2-3 µm), filiform caulocystidia up to 165 mm long, and basidiome formation on grass leaves (fide Singer, 1976).

Material examined. - NEW ZEALAND: South Island, Prov. Nelson, Kaihoka Reserve, 10 V 1968, Horak 68-410 (Holotype, PDD; Isotype, SFSU, ZT).