Full name: Hebeloma microsporum (Alessio & Nonis) Contu (2008)
Published: Bollettino della Associazione Micologica ed Ecologica Romana 73-74 (1-2): 16 (2008)
Taxonomic status: We have not been able to unambiguously determine the current genus of this name.
Basionym: Hebelomina microspora Alessio & Nonis (1977)

Types: ITALY: Bruno Nonis, Parco della Rimembranza Augustae Taurinorum, 5 May 1976, E. Rebaudengo (Holotype. held at herbarium Venetian Herbarium Museum of Monte Ceva at Battaglia Terme, HJB1000256).

Original diagnosis: Pileus e convexo expansus, cuticula modice fibrosa, in junioribus albide-ochraceo pallida, in evolutis sublateritio-brunneola. Lamellae emarginatae, initio cremeo-albidae dein lateritio-soffusae demum fusco-ochraceo-brunnae. Stipes concolor pileo, subtiliter summo pruina albida pulverulentus. Caro confluens, odore in matures farinaceo-rancido, sapore amarello, ubique albido-cremea. Sporea ovoideo-amigdaliformes, qiuasi hyalinae sed in chloralio-jodato griseo-caerulescentes; cystidia in acie lamellarum multiformia. In silvis coniferarum, ad ligna et radices, vere autumnoque.

English translation: Pileus convex then expanding, with moderately fibrous cuticle, pallid white-ochre when young, then pale brick-coloured finally brown-ochre. Lamellae emarginate, whitish-cream at first, then dull brick-coloured finally ochre-brown. Stipe with same colour as pileus, subtly pulverulent at apex with white pruina. Context confluent, odour in mature state mealy-rancid, taste slightly bitter, white-cream all over. Spores ovoid-amygdaloid, quasi hyaline but in Melzer’s reagent greyish-bluish; cystidia on lamella edge variably shaped. In coniferous forest, on wood and roots; spring and autumn.

Commentary: Alessio & Nonis (1977) originally erected this species to replace Hebelomina microspora Huijsman (Huijsman 1946: 31), invalidly published without a Latin diagnosis (Art. 39.1; McNeill et al. 2012). Contu (in Cittadini et al. 2008) transferred the species of Alessio & Nonis to Hebeloma, without true conviction (“almeno temporaneamente”) and without having seen the type. However, some information given in the original description and the protologue, in particular the amyloidity of the spores, argues strongly against the assignment to Hebeloma. The habitat, growing on wood, though not unseen in ectomycorrhiza formers, is not in favour of an assignment to any genus of ectomycorrhizal fungi. We have examined the holotype of this taxon, which is not in good condition. We have not been able to find any spores. However, the cheilocystidia and pleurocystidia, the latter being numerous, do not correspond to any Hebeloma we have ever seen and are more like those found in taxa like Baeospora. While we are uncertain of the genus it is certainly not a Hebeloma. Molecular data from the type suggests it may be distantly related (although by no means clearly) to Baeospora and the Australian genus Pleurella that have been tentatively placed in the Cyphellaceae (Sánchez-García et al. 2014, supplement). There is no close sequence match for the ITS of this collection, but a reasonably good LSU match (99%, 601 bp) to the sequence of a collection originally identified as Hydropus scabripes (AF042635; Bodensteiner et al. 2004). In the molecular analysis published in this work and in fig. 6, it is in a rather isolated position in relation to other members of the genus Hydropus. Possibly prompted by the result of Bodensteiner et al. (2004), Redhead (2013) erected the monospecific genus Mycopan for Hydropus scabripes. If the type of Mycopan is indeed the same species as collection DAOM192847, then it would appear likely that Hebeloma microsporum is a member of Mycopan. The basionym of M. scabripes is Prunulus scabripes Murrill (Murril 1916). It was recombined by Singer (1961[1962]) into Hydropus. The type of M. scabripes has been described by Murrill (1916) and Maas Geesteranus & Hausknecht (1993) cite some results of type studies of C. Bas. A few additional details are given in Bas (1999). Alessio & Nonis (1977) described the type they assigned to Hebeloma microsporum. Based on these descriptions and our own observations, it is not possible to conclude whether M. scabripes and Hebeloma microsporum may be congeners or even conspecifics. The latter does not appear likely. With regard to some important characters, even though the spore size roughly corresponds between the descriptions of Murrill (1916) and Alessio & Nonis (1977), the spore size cited in Maas Geesteranus & Hausknecht (1993) is larger. (This could be due to two-spored basidia in part of the material: Bas (1999) described the basidia as two-spored in the material he saw; neither Murrill (1916) nor Alessio & Nonis (1977) described the basidia; we saw four-spored basidia in the type material of Hebeloma microsporum.) The description of the spore shape differs between Murrill (1916) and Alessio & Nonis (1977), as does the description of the stipe surface at the apex (minutely and densely scabruous versus pruinose). Also important is the difference in habitat, “in grass at roadside in thin woods” (Murrill 1916) vs. growing on wood (Alessio & Nonis 1977). We are aware of several sequenced collections identified as Hydropus scabripes or similar species (i.e. Hydropus trichoderma or Hydropus paradoxus), of which some – represented by PBM2513 in fig. 6 – are molecularly closely related to each other. Based on the available data and in the absence of molecular data from the type of M. scabripes, we suspect the majority opinion is that, if the type of M. scabripes was sequenced, it would fall into this group. However, we have come across a number of presumably misidentified collections of Hydropus scabripes (data not published) of widely differing taxonomic associations. A single probably misidentified collection (STU HKr0681/91), originally identified as Hydropus scabripes, is even closely related to DAOM196062, allegedly representing the type species of Hydropus, Hydropus fuliginarius. None of the other sequences identified as Hydropus scabripes (Hydropus paradoxus, Hydropus trichoderma) is closely related to Hebeloma microsporum or Hydropus scabripes DAOM192847 (fig 6). Thus, not knowing the rationale behind Redhead’s (2013) erection of Mycopan, it is not clear to what genus Hebeloma microsporum should be assigned, but it is clearly not a member of Hebeloma. Following the recommendations of Vellinga et al. (2015), it would be premature to make any taxonomic changes or erect a new genus at this time.