Albomagister griseosquamosus Lebeuf, Matheny & Vellinga 2024, sp. nov.

Albomagister griseosquamosus Lebeuf, Matheny & Vellinga, sp. nov. (Figs. 2A–2F, 3A, 6A–6C) MYCOBANK: MB851399. TYPE: USA, Tennessee, Sevier County, Great Smoky Mountains National Park, Elmont, Jakes Creek Trail (35.6764 -83.3971), in humus in acidic cove hardwood forest under various hardwoods and Tsuga canadensis, 4 August 2009, J. Lennie ECV4038 (holotype designated here, TENN-F-064609). DIAGNOSIS: Differs from the white species of Albomagister by the gray squarrose to appressed-scaly pileus and stipe. Habit tricholomatoid. Pileus 25–50 mm wide, campanulate to plano-convex and at times with a low broad umbo, more flattened with age; margin decurved, occasionally torn or undulating; surface dry, initially with a whitish ground color, becoming gray and completely covered with dense small dark gray to blackish squamules, these squarrulose when young and more like fibrillose-scales in more-or-less concentric bands in age, not hygrophanous; context pale gray with dark gray areas, odor, and taste indistinct, absent, or mild. Lamellae sinuate to adnate, close to crowded with ca. 55–60 L and 1–3 tiers of lamellulae, thick, narrow (3–5 mm), white to pale gray or gray with white edges that darken to gray, edges sometimes eroded. Stipe 35–70 × 4–7 mm, equal to slightly narrowed or slightly enlarged at the base; surface dry, veil absent, fibrillose at the apex but mostly with gray scaber-like squamules or with the squamules covering the entire length on a whitish or paler background, squamules smaller towards the base, becoming lacerate-scaly with age; context pale gray, becoming paler towards the nearly white base; hollow. Basidiospores 6– 7.1 –8 × (4)4.5– 5.6 –6.7 µm, Q 1.10– 1.28 –1.57 (n = 65/4), smooth, elliptic to broadly so or subglobose, with a guttule, hyaline, inamyloid, with a distinct apiculus, white in deposit. Basidia 25– 37 × 7–9.5 µm, 4-spored, clavate to subcylindric, hyaline. Pleurocystidia 38–74 × 11–20 µm, obovate, sphaeropedunculate, broadly clavate, or fusiform-rostrate, with a long pedicel, with a rounded or mucronate apex, with thin or slightly thickened wall, brown pigmented. Cheilocystidia forming a sterile lamellar edge, 24–80 × 7–15 µm, often narrowly lageniform to abruptly fusiform, very long pedicellate, walls slightly thickened and brown pigmented. Pileipellis an irregular trichoderm with chained elements, these narrowed gradually, hyphae incrusted; terminal cells 45–115 × 9–18 µm, utriform to somewhat conical, less often narrowly lageniform, base generally broad, apices often with a moniliform excrescence, at times rostrate, brownish pigmented. Stipitipellis similar to pileipellis. Clamp connections present, large, and conspicuous. TAXONOMIC NOTES: Albomagister griseosquamosus was previously reported as “undet gray scaly” in Sánchez-García et al. (2014, 2017). This species resembles Tricholoma squarrulosum Bres. and T. atrosquamosum Sacc., but in its outward appearance A. griseosquamosus differs from these by the more elongated non-bulbous stipe and non-farinaceous odor and taste. Microscopically, A. griseosquamosus differs readily from these by the presence of distinct pleuro- and cheilocystidia and the large conspicuous clamp connections found throughout the all tissues. The basidiospores of the Quebec collections (6– 6.5 –7.5 × 4– 4.8 –5) µm, Q 1.09 – 1.30 –1.63 are somewhat smaller than the type and ECV5690 from Tennessee. Although not analyzed here, an rpb1 sequence was also produced from the type of A. griseosquamosus —— KU139073 (Sánchez-García and Matheny 2017). ETYMOLOGY: griseosquamosus (Latin), gray scaly, in reference to the gray scales on the pileus and stipe DISTRIBUTION AND ECOLOGY: Albomagister griseosquamosus apparently is widely distributed in eastern North America, having been found in both Quebec and Tennessee, although there is a broad sampling gap between these regions. It occurs on acidic soils (where known) at relatively low elevations (<600 m), in mixed and cove hardwood forests containing some mixture of the following ectomycorrhizal trees: Abies, Fagus, Betula, Tsuga and/or Tilia. Basidiomes have been observed August to September. OTHER SPECIMENS EXAMINED: Canada, Quebec, Saint-Stanislas, Parc de la rivière Batiscan, secteur Murphy, trial Le Buis (46.5891 -72.4125), solitary on ground in leaf litter in mixed forest under Abies balsamea, Betula alleghaniensis, 7 September 2020, R. Lebeuf & A. Paul HRL3282 (DAOM 984972); Saint-Alexis-des-Monts, chemin Yvon-Plante (46.5099 -73.1955), gregarious on soil in northern hardwood forest under Fagus grandifolia, Abies balsamea, Acer, 16 Aug. 2023, R. Lebeuf & A. Paul HRL4268 (R.L. pers. fung., iNat178773906). USA, Tennessee, Sevier Co., Great Smoky Mountains National Park, Greenbrier, Ramsey Cascades Trail (35.7028 -83.3575), acidic cove hardwood forest including Tsuga canadensis, Betula alleghaniensis, Tilia americana, Quercus, 5 September 2013, E. C. Vellinga ECV5690 (TENN-F-068763).