NEW ZEALAND: North Island, Northland, Hokianga Co., Waipoua Kauri Reserve, 12.V.83, R. H. Petersen no.55634 [Holotype, TENN no. 44402].

Basidiomata marcescent. Pileus 0.5-l mm diam, convex, expanding to plano-convex; surface even (non-striate), minutely granulose, white. Lamellae absent; hymenophore smooth, white. Stipe 0.5-1 x 0.1 mm, central or slightly eccentric, often curved, terete, equal, pruinose, insititious, white overall. Odour and taste not recorded. Basidiospores 12.8-17.2 x 3.8-4.8 µm [x = 14.7 x 4.2 µm, s = 1.3 x 0.3, E = 2.7-4.4, Q=3.5, sQ = 0.4, n = 20], subfusiform, inequilateral in profile, hyaline, inamyloid, smooth. Basidia 24-32 x 6.5-8.0 µm, tetrasporic, cylindric or subclavate, hyaline, contents tawny in Melzer's reagent. Basidioles clavate or ventricose. Hymenial cystidia ~32 x 10 µm, lageniform or ampullaceous, non-refractive, hyaline, thin-walled or firm-walled (walls up to 0.5 µm thick). Pileipellis hymeniform; elements up to 28 µm diam, smooth (non-diverticulate), broadly clavate or vesiculose and short pedicellate, hyaline, inamyloid; walls up to 1 µm thick; ventricose dermatocystidioid elements scattered, scarcely projecting. Tramal hyphae 3-8(-13) µm diam, interwoven, hyaline, inamyloid, non-gelatinous, clamped; walls <l µm thick. Stipe tissue monomitic. Stipe cortical hyphae 3-10 µm diam, parallel, hyaline, inamyloid, smooth, clamped; walls up to 2 µm thick. Stipe medullary hyphae similar but thin-walled. Caulocystidia scattered, 4-16 x 6-9 µm, cylindric or clavate, thick-walled, hyaline, inamyloid. Scattered on senescent monocotyledonous leaves (probably Astelia).

Pileus 0.5-1 mm latus, convexus vel plano-convexus, albus. Lamellae nullae. Stipes 0.5-1 x 0.1 mm, centralis vel eccentricus, falcatus, pruinosus, insititius, albus. Basidiosporae 12.8-17.2 x 3.8-4.8 µm, subfusiformes, laeves, hyalinae, inamyloideae. Basidia tetraspora, Hymenii cystidia lageniformia. Pileipellis hymeniformis ex elementis clavatis vel vesiculosis, hyalinis; dermatocystidia rara. Trama ex hyphis inamyloideis, fibulatis. Caulocystidia clavata vel cylindrica, crassitunicata. In foliis monocotyledonum.

Marasmius pusillissimus is characterised by minute, entirely white basidiomata that lack lamellae, pruinose, insititious stipe, and growth on monocotyledonous leaves. In addition, inamyloid, clamped tramal hyphae and long spores are distinctive. Although basidiomata size, stature and reduced hymenophore suggest that this taxon should be looked for in the cyphelloid series of the Tricholomataceae, several features indicate that the species is best placed in Marasmius sect. Epiphylli Kuhner subsect. Epiphyllini Singer. Characters which support this disposition include: a) hymeniform pileipellis of smooth, non-diverticulate elements plus scattered dermatocystidioid cells; b) inamyloid tramal hyphae with clamp connections; c) ventricose-ampullaceous hymenial cystidia; d) absence of pigments; and e) insititious stipe. Taxa in sect. Epiphylli show hymenophore development ranging from well-developed lamellae to radiating folds or ridges, but few taxa form hymenia entirely devoid of macroscopic differentiation. One such species superficially similar to M. pusillissimus is M. martinii Singer [ut M. martini (Singer, 1958) nom. nov. for Cymatella longipes Martin (1944)]. Both M. pusillissimus and M. martinii form very small, pigmentless pilei with entirely smooth hymenia. Marasmius martinii differs in forming a longer (up to 16 mm) and darkly pigmented stipe (yellow-brown or nearly black), shorter spores (9-11 µm), and in growing from bark of fallen branches [fide Martin 1944; Singer 1965, 1976]. Marasmius martinii is known only from Colombia, South America.
A second species superficially similar to M. pusillissimus was described from Sierra Leone as Marasmius cymatelloides Dennis & Reid (1957). Subsequently, Singer (1961) established the monotypic genus Palaeocephala Singer based on the type specimen of M. cymatelloides. Palaeocephala is closely allied with Gloiocephala Massee, a genus considered by some as congeneric with Marasmius (see Bas 1961; Noordeloos 1981). Palaeocephala cymatelloides differs from M. pusillissimus in having dextrinoid tramal hyphae, abundant basal mycelium (i.e., stipe non-insititious), absence of hymenial cystidia, and in growing on leaves of Baphia pyrifolia Baill. [Leguminosae] (fide Dennis & Reid 1957).

Holotypus: TENN no. 44402.

NEW ZEALAND: North Island, Northland, Hokianga Co., Trounson Kauri Park, 13.V.83, G. Samuels (R. H. Petersen no. 55648) [Holotype, TENN no. 44415]; Waipoua Kauri Reserve, 12.V.83, R. H. Petersen no. 55638 (TENN no. 44419].

Basidiomata marcescent. Pileus 0.2-0.5 mm diam, convex, deeply sulcate; surface granulose, white overall. Lamellae adnate or slightly adnexed, with or without a poorly developed collarium, remote (3-5 complete lamellae), broad, white; edges granulose; lamellulae absent. Stipe 0.5-1 x 0.1 mm, central, curved due to geotropic hymenophore, filiform, terete, equal, white overall; surface glabrous above, basal region with a few mycelial hairs, subinsititious, often with a socle-like base surrounded by a small ring of radiating hairs. Rhizomorphs absent. Odour and taste not recorded.
Basidiospores 7.8-9.6 x 4.0-4.8 µm [x = 8.6 x 4.4 µm, s = 0.5 x 0.3, E = 1.7-2.1, Q = 1.9, sQ = 0.1, n = 20], ellipsoid or amygdaliform, hyaline, inamyloid, smooth. Basidia 16-20 x 8-10.5 µm, tetrasporic, broadly clavate. Basidioles broadly clavate. Pleurocystidia absent. Cheilocystidia common nearest pileus margin, scarce nearest stipe, similar to the pileipellis elements. Pileipellis hymeniform, of Rotalis-type elements, 12-20 x 8-16 µm, broadly clavate or sphaeropedunculate, hyaline, inamyloid, thin-walled; diverticula 1.0-2.5 x 0.5-1.5 µm, cylindric-obtuse, hyaline, thick-walled. Tramal hyphae interwoven in pileus, subparallel in lamellae, 2.5-4.0 µm diam, non-inflated, non-gelatinous, hyaline, inamyloid or weakly dextrinoid, thin-walled, clamp connections common; refractive oleiferous hyphae occasional. Stipe tissue monomitic; cortical and medullary hyphae similar, parallel, 2.0-7.2 µm diam, hyaline throughout, strongly dextrinoid, thin-walled, smooth; clamp connections absent. Stipe vesture absent near apex, consisting of a few erect, filiform, mycelial "hairs" nearest the base; caulocystidia absent. Scattered on senescent leaves of Gahnia sp. [Cyperales].

Pileus 0.2-0.5 mm latus, convexus, sulcatus, albus. Lamellae adnatae, collariatae, remotae, albae. Stipes 0.5-1 x 0.1 mm, centralis, falcatus, subinsititius, albus. Rhizomorphae nullae. Basidiosporae 7.8-9.6 x 4.0-4,8 µm, ellipsoideae vel amygdaliformes, laeves, hyalinae, inamyloideae. Basidia tetraspora. Pleurocystidia nulla. Cheilocystidia elementis pileipellis similia. Pileipellis hymeniformis ex elementis M. rotali similibus; diverticuli hyalini. Trama ex hyphis inamyloideis vel dextrinoideis, raro Fibulatis. Stipes ex hyphis dextrinoideis, defibulatis. Caulocystidia nulla. In foliis Gahniae.

Diagnostic features of M. rosulatus include: a) minute stature, with pilei reaching 0.5 mm diameter and stipes up to 1 mm long; b) reduced number of well-developed lamellae (3-5 present, no lamellulae) and a poorly developed (or absent) collarium; c) complete lack of pigments throughout the basidiomata; d) clamp connections on tramal hyphae and hymenial elements but absent in stipe tissue; e) strongly dextrinoid stipe tissue; f) subinsititious stipe with radiating basal mycelial hairs; and g) growth on senescent leaves of Gahnia.
We were unable to demonstrate the presence of a collarium in the holotype specimen, but a second, conspecific collection contains several basidiomata, which readily show a thin layer of tissue connecting the lamellae and sheathing the stipe apex. Presence of a collarium, albeit very weakly developed, in combination with dextrinoid stipe tissue and Rotalis-type pileipellis elements dictates placement in sect. Marasmius subsect. Marasmius [= subsect. Pararotulae Singer (1976)]. It must be noted, however, that a subinsititious stipe and a complete absence of pigments exhibited by M. rosulatus are characters unusual in sect. Marasmius. Within subsect. Marasmius, M. rosulatus is most phenetically similar to M. pararotula Sing., described from Bolivia. Both species form minute, white pilei with few, broad lamellae. Marasmius pararotula differs in forming a deep umber, longer (5-12 mm) and strictly insititious stipe, more lamellae (5-8), broader spores (4.8-5.5 µm diam.), and in growing on leaves of dicotyledonous plants (Fide Singer 1965).

Holotypus: TENN no. 44415.