Full name: Hebeloma platense Speg. (1898)
Published: Anales del Museo Nacional de Historia Natural Buenos Aires 6: 128 (1898)
Taxonomic status: We have not been able to unambiguously determine the current genus of this name.
Original diagnosis: Diag. Denudatuam pusillum subcaespitosum pileo convexulo exumbonato nudo isabellino laevi glabro, margine umbrino, udo hygrophano striato, lamellis sinuato-adnatis concoloribus, stipite cavo albo, basi vix incrassato primo Iaevi dein plus minusve squamoso-ftbroso; sporis laevibus umbrinis. Hab. Ad folia putrescentia coacervata et ad quisquilias in umbrosis prope La Plata, Fbr. 1892. Obs. Saepius caespitosum sed etiam laxe gregarium v. subsolitarinm; pileus membranaceo-carnosulus, primo e globoso subcampanulatus isabellinus, margine non v. vix inflexulus, saepins exumbonatus dein gradatim expansus postremo applanatus (2-6 cm. diam.), in senectute lacerus v. subrevolutus atque centro non v. vix subumbilicatus, siccus glaber laevis (sed oculo nudo fere velutino-pulverulentus) opacus non striatus, ambitu saepe obsolete radiatim rugulosus. margine integer, udus hvgrophanus umbrinus ad medium usque obscurius lineatus; cutis e cellulis obovatis dense constipatis contexta; caro tenuis ex albo subfuscescens laxe fibrosulo-farinosula; lamellae polymacriae postice sinuato-v. truncatoadnatae, antice attenuato-rotundatae obtusiusculae contertae latiusculae (13-6 mm lat.) isabellinae acie integerrima angustissime pallidiore donatae, siccae membranaceo-molles flexiles, udae rigidulae fragiles, a stipite facillime secedentes sed pileo arcte adnatae; stipes albus rectus rectus v. leniter flexuosulus, teres (25-50 mm long. = 2,5 mm diam.) intus late fistulosus, siccus dense squamoso-fibrillosus apice striatulus atque rarius subtortus, udus hygrophanus, basi non v. vix incrassatulus atque squarrulosus cum pileo continuus. Sporae ellipticae (8-10 μ long. = 5-6 μ diam.) isabellinae; basidia clavulata (20 μ long. = 7 μ diam.); cystidia in margine lamellarum valde evoluta clavulata (30-40 μ long. = 12-14 μ diam.). Species ad Naucorias nonnihil vergens sed stipite carnosulo pileo carnosulo-flaccidulo melius Hebelomatibus adscribenda.

English translation: Bare diminutive subcaespitose with slightly convex pileus not umbonate naked dingy yellowish-whitish smooth, glabrous, with dark margin, hygrophanous striate when moist, lamellae sinuate-adnate concolorous, stipe fistulose white, hardly enlarged at base at first smooth then more or less squamose-fibrous; spores smooth brown. Hab. On heaps of rotting leaves and on rubbish in shaded places near La Plata, Feb. 1892. Obs. More frequently caespitose but also loosely gregarious or solitary; pileus membranaceous hardly fleshy, at first globose subcampanulate dingy yellowish-whitish, margin not or slightly inflexed, more frequently non-umbonate, then gradually expanded finally applanate (2-6 cm. diam.), with age lacerate or subrevolute and not or slightly umbilicate in the centre, dry glabrous smooth (but to the naked eye almost velutinous-pulverulent) opaque non-striate, on the margin often indistinctly radially rugulose, margin entire, when moist hygrophanous brown, marked with fine brown lines up to the middle; cutis made up of densely-packed obovate cells; context thin white to light brownish, loosely slightly fibrous-mealy; lamellae of various length, at the attachment sinuate or truncate-adnate, at the outermost end attenuate-rounded somewhat blunt crowded moderately broad (13-6 mm broad) isabelline (greyish-yellow), with an edge absolutely smooth very narrow and paler, membranaceous-soft when dry, slightly rigid fragile when moist, very easily separating from the stipe, but firmly adnate to the pileus; stipe white straight or slightly flexuous, equal (25-50 mm long, 2.5 mm thick) inside broadly fistulose, when dry densely squamose-fibrillose, with the apex slightly striate and more rarely slightly twisted, when moist hygrophanous, not or slightly enlarged at base and squarrulose confluent with the pileus. Spores elliptic (8-10 μ long = 5-6 μ wide) dingy yellowish-whitish; basidia clavuliform (20 μ long = 7 μm wide); cystidia on lamellar edge strongly developed, small clavate (30-40 μ long = 12-14 μ wide). A species to some extent tending to Naucorias, but for the somewhat fleshy stipe and slightly fleshy-flaccid pileus better to be ascribed to Hebelomas.

Commentary: Within the latin diagnosis, *”Denudatum” (denuded, bare, stripped of covering) is ambiguous. It may refer to the lack of veil (Fries’ Denudati) or it may simply be a synonym of glabrous, lachink scales etc. The term "polymacriae" is a Greek compound, rarely used and taken to mean “of many dimensions”; referring to lamellae it probably should be interpreted as “of various length”. Thus far we have been unable to study type material of this taxon. Based on the diagnosis, it is not possible to determine whether this is a Hebeloma.