Tricholomataceae section Pseudobaeosporoideae Vizzini, Consiglio & Setti, 2025

Vizzini, Alfredo, Consiglio, Giovanni, Adamčíková, Katarína, Setti, Ledo & Adamčík, Slavomír, 2025, Pseudobaeosporoideae, a new subfamily within the Tricholomataceae for the genus Pseudobaeospora (Agaricales, Tricholomatineae) based on morphological and molecular inference, IMA Fungus 16, pp. e 144994-e 144994 : e144994-

Tricholomataceae section Pseudobaeosporoideae Vizzini, Consiglio & Setti subfam. nov.

Diagnosis.

Basidiomes agaricoid (pileostipitate), gymnocarpic (no veils), mostly mycenoid or rarely collybioid, homogeneous (context of stipe and pileus continuous), hymenophore lamellate, lamellae adnexed, decurrent with a tooth to almost free or free, spore deposit white to whitish, basidiospores usually smooth, when mature usually thick-walled, non-amyloid, often weakly to strongly dextrinoid, basidia non-siderophilous, sometimes thick-walled and sclerified (wall 1–3 µm thick, crassobasidia or sclerobasidia) and dextrinoid, hymenophoral trama regular to subregular, hymenial cystidia absent or present as cheilocystidia, rarely as pleurocystidia, caulocystidia usually present, pileipellis a cutis to trichoderm or pluristratous hymeniderm / epithelium / celluloderm, pileocystidia-like elements rare, clamp-connections present or absent, hyphal system monomitic. Terrestrial, trophic mode unknown, presumably saprotrophic or forming an unspecified symbiotic interaction with vascular plants.

Type of the subfamily.

Pseudobaeospora Singer , Lloydia 5: 129 (1942).

Type of the genus.

Baeospora oligophylla Singer , Revue Mycol., Paris 3 (4–5): 194 (1938) = Collybia pillodii Quél. [as ‘ pillodi’], C. r. Assoc. Franç. Avancem. Sci. 18 (2): 509 (1890).

Representative genus.

Pseudobaeospora .

Notes.

The subfamily is currently monogeneric and is sister to the core of the Tricholomataceae [ Tricholomataceae subfam. Tricholomatoideae (Singer) Bon] (Figs 1 , 2 ) within the Tricholomatineae . Pseudobaeospora is circumscribed by small mycenoid (e. g., P. celluloderma ) to collybioid white-spored basidiomes [indicatively, pileus 1.5–30 mm in diam., stipe 10–55 (– 70) × 0.5–3.0 mm]; pileus frequently with pale to dark lilac, violaceous, purple, blue tinges, hemispherical, obtusely conical or paraboloid to plano-convex or plano-conical (campanulate); lamellae adnexed, emarginate, or decurrent with a tooth to free, usually more or less concolorous with pileus; stipe pruinose to fibrillose, often rooting, at base mostly with white to rarely yellow tomentum and rhizomorphs; basidiospores small (from 2.5 µm to rarely more than 6.5 µm long), subglobose to broadly ellipsoid, colorless, smooth (minutely rugulose under SEM in P. wipapatiae Desjardin, Hemmes & B. A. Perry, Desjardin et al. 2014 ), pore-less, with very distinct, abrupt hilar appendage, at first thin-walled and non-amyloid, then becoming thick-walled and weakly to strongly dextrinoid, congophilous, cyanophilous, and rather frequently more or less metachromatic in Cresyl blue (e. g., P. paulochroma Bas , P. bavariae Bas ); basidia 4 - spored to 2 - spored, or 4 - and 2 - spored in the same basidiome, often with a basal clamp-connection, without inner siderophilous granulations, scattered sclerified (thick-walled) dextrinoid basidia (sclerobasidia, crassobasidia following Singer and Clémençon 1972, Watling and Chandra 1983, and Clémençon 2004) often present; pleurocystidia usually lacking (rarely present, e. g., P. aciculifera Voto & Soop , P. cyanea , P. taluna ) and cheilocystidia present in some species, in one case with amyloid contents ( P. wipapatiae ); hymenophoral trama regular to somewhat irregular, with elements in central part (mediostratum) often inflated; pileipellis varying from a simple cutis or cutis-trichoderm to a trichoderm in some species to an irregular pluristratous hymeniderm / epithelium / / celluloderm in others; some terminal elements could be differentiated as pileocystidia; hyphae thin-walled, not or slightly gelatinized; pigments predominantly parietal (sometimes also hyphae with minute extracellular incrustations) but also intracellular (vacuolar or cytoplasmatic); in 5 % KOH pileipellis fragments usually changing colour or becoming violet, green, yellow or brownish with such tinges, rarely first red then yellow-green; in several species pseudotissues more or less dextrinoid; caulocystidia usually present at least at stipe apex, thin-walled, scattered to clustered; clamp-connections usually present in several or all tissues, rare in P. calcarea , in one species restricted to basidia and subhymenium ( P. frieslandica Bas ) or absent (e. g., P. pillodii ).

The species show a terrestrial habit, usually on needle carpets of conifers, forest litter, wooden debris, humus, deeply hidden among / on mosses and grasses but also sometimes on bare soil ( Bas 2002, 2003). Their trophic status remains unknown, presumably saprotrophic, non-ectomycorrhizal ( Bas 2002, 2003; not reported in Rinaldi et al. 2008, Tedersoo et al. 2010, and Tedersoo and Smith 2013). As noted by Ronikier and Moreau (2007), most species appear to prefer calcareous and / or nutrient-rich soils, but some are found on peaty soils.

The unique combination of small-sized mycenoid to collybioid basidiomes often with lilac violet tinges, pileipellis usually positively reacting with KOH, presence of scattered dextrinoid thick-walled basidia and small-sized spores becoming secondarily thick-walled and dextrinoid makes this genus easily identifiable and delimitable. Thickening spore walls becoming dextrinoid typically occurs also in the genus Rhodocollybia Singer ( Omphalotaceae Bresinsky , Marasmiineae Aime, Dentinger & Gaya) ( Antonín and Noordeloos 1997, 2010) and is considered a generic character. Rhodocollybia however differs in larger spores, larger basidiomes with a simple ixocutis, absence of crassobasidia, a pinkish yellow to pinkish brown, never white spore deposit, and a different (contradictory) trophic habit, viz. putatively EcM ( Pera and Alvarez 1995; Mleczko 2004; Schirkonyer et al. 2013) to facultatively biotrophic saprobe (secondary colonizers of senescent EcM root tips, Tedersoo et al. 2010; Tedersoo and Smith 2013).

Crassobasidia (non-dextrinoid) are occasionally present in different suborders of Agaricales : Armillaria (Fr.) Staude and Xerula Maire / Hymenopellis R. H. Petersen ( Physalacriaceae Corner ) within Marasmiineae ( Singer and Clémençon 1972; Watling and Chandra 1983; Watling 1992; Clémençon 2004; Antonín and Dvořák 2010; Petersen and Hughes 2010); Amanita Pers. ( Amanitaceae E. - J. Gilbert ) within Pluteineae Aime, Dentinger & Gaya ( Kotilová-Kubičková and Pouzar 1988; Tulloss and Halling 1997); Clavaria stellifera J. Geesink & Bas , Camarophyllopsis Herink s. l. and Ramariopsis (Donk) Corner ( Clavariaceae Chevall. ) within Clavariineae Olariaga, Huhtinen, Læssøe, J. H. Petersen & K. Hansen ( Singer 1986; Geesink and Bas 1992; Halama et al. 2017); Crepidotus (Fr.) Staude ( Crepidotaceae (S. Imai) Singer ) and Inocybe (Fr.) Fr. s. l. ( Inocybaceae Jülich ) within Agaricineae Fr. ( Kuyper 1986; Senn-Irlet 1995); Calocybella Vizzini, Consiglio & Setti ( Lyophyllaceae Jülich ), Fayodia Kühner ( Fayodiaceae Jülich ), Dermoloma J. E. Lange ex Herink ( Tricholomataceae ) and Entoloma (Fr.) P. Kumm. ( Entolomataceae Kotl. & Pouzar ), within Tricholomatineae ( Singer 1986; Arnolds 1993; Horak and Desjardin 1993; Manimohan et al. 1995; Latha et al. 2020). Their presence is a generic character only for Armillaria and Camarophyllopsis s. l. ( Singer 1986).

The microchemical reaction, 5 % KOH pileipellis fragments which commonly become blue green is reminiscent of that exhibited by some Gymnopus (Pers.) Gray species allied with G. alkalivirens (Singer) Halling ( Halling 1979, 1981, 1990; Antonín and Noordeloos 1997, 2010) ( Omphalotaceae , Marasmiineae), Xerophorus (Bon) Vizzini, Consiglio & M. Marchetti ( Vizzini et al. 2020 a) ( Callistosporiaceae Vizzini, Consiglio, M. Marchetti & P. Alvarado , Tricholomatineae) and Leucoagaricus Locq. ex Singer / Leucocoprinus Pat. species ( Agaricaceae , Leucocoprineae Singer, Bon 1993; Vellinga et al. 2010; Asif et al. 2024; Kooij et al. 2024; Yang et al. 2024).

With the exclusion of Pseudobaeospora ( Tricholomataceae subfam. Pseudobaeosporoideae ) from the family core Tricholomataceae ( Tricholomataceae subfam. Tricholomatoideae) the latter subfamily is thus restricted to species characterized by a mostly tricholomatoid or rarely tricholomatoid-collybioid habit ( Dennisiomyces , Dermoloma ), with smooth or verrucose ( Leucopaxillus ) non-dextrinoid and thin-walled basidiospores, whose walls usually react in grey or blue to Melzer’s reagent (immediately amyloid, Albomagister partim, Dermoloma subg. Amylospora Adamčík , Corneriella , Dennisiomyces , Leucopaxillus , Porpoloma , Pseudoporpoloma and Pseudotricholoma ; latently amyloid, Tricholoma ; see Moreau et al. 2015; Vizzini et al. 2016, 2020 b, 2024; Corriol and Jargeat 2018; Sánchez-García et al. 2021; Matheny et al. 2024).

Figures

Figure 1. Bayesian inference phylogram built with nucleotide sequence data of four loci (nrLSU, nrSSU, RPB 2 - exons and TEF 1 - exons) of the main lineages inside the suborder Tricholomatineae of the order Agaricales, rooted with Suillus pictus (Boletales), Ampulloclitocybe clavipes and Pseudoarmillariella ectypoides (Hygrophorineae, Agaricales) as outgroups. Nodes were annotated with Bayesian PP (left) and ML BP (right) values, with the significance threshold considered as Bayesian PP ≥ 0.95 and / or ML BP ≥ 70 %. Subsignificant support values were annotated in parentheses. All family-level clades, except for Tricholomataceae, were collapsed. Boldface names represent samples sequenced for this study.

Figure 2. Mid-point rooted Bayesian phylogeny (nrITS, nrLSU, nrSSU, RPB 2 - exons) of the Tricholomataceae s. s. Nodes were annotated with Bayesian PP (left) and ML BP (right) values, with the significance threshold considered as Bayesian PP ≥ 0.95 and / or ML BP ≥ 70 %. Subsignificant support values were annotated in parentheses. Boldface names represent samples sequenced for this study.