Pseudotomentella atrofusca M.J.Larsen, Bull. Torrey Bot. Club. 98: 39 (1971)

Svantesson, Sten, Larsson, Karl-Henrik, Koljalg, Urmas, W. May, Tom, Patrik Cangren,, Henrik Nilsson, R. & Larsson, Ellen, 2019, Solving the taxonomic identity of Pseudotomentellatristis s. l. (Thelephorales, Basidiomycota) - a multi-gene phylogeny and taxonomic review, integrating ecological and geographical data, MycoKeys 50, pp. 1-77 : 22-25

Pseudotomentella atrofusca M.J.Larsen, Bull. Torrey Bot. Club. 98: 39 (1971) Fig. 10

Type.

UNITED STATES. Arizona: Fort Valley, Coconino, on Pinus ponderosa Laws., 21 September 1967, R. L. Gilbertson 7553 (holotype: ARIZ!, GenBank Acc. No. ITS: MK290732; isotype: SSMF 685-4578).

UNITE SH.

SH005338.07FU

Description.

Basidiome annual, resupinate, membranaceous, effused. Mature parts continuous, with a cottony texture. Hymenium smooth, brown. Immature parts discon tinuous, byssoid, with a cottony texture. Subhymenium and hymenium of immature parts initially whitish-grey to whitish-grey brown, when more mature blue grey to brown grey. Subiculum thin, loose, fibrous, pale brown; often forms the outer edge of the basidiome, extending noticeably beyond the hymenium. All characters recorded in dried state.

Hyphal cords connecting to the edge of the basidiome and thinning out underneath; whitish to pale brown. Individual cords dimitic; formed by a sheathing layer of skeletal hyphae and two layers of generative hyphae; the outer generative hyphae thinner and the inner ones wider, the latter often swollen interseptally. Skeletal hyphae 1.1-1.4 (-1.5) μm wide, with a mean width of 1.3 μm. Outer generative hyphae (2.2) 2.3-2.9 μm wide, with a mean width of 2.6 μm. Inner generative hyphae (3.8) 3.9-5.3 (5.5) μm wide, with a mean width of 4.5 μm. All hyphae pale yellowish-brown in both KOH and water.

Hyphal system dimitic, clamp connections and reaction in Melzer’s reagent absent from all hyphae.

Subicular hyphae of two kinds: (1) generative hyphae noticeably long and straight, thick-walled; forming a loose tissue, in which (2) skeletal hyphae occur sparsely (most common in areas to where hyphal cords attach). Generative hyphae (1.7-) 1.8-2.8 μm wide, with a mean width of 2.3 μm; pale yellowish-brown to yellowish-brown in both KOH and water. Skeletal hyphae with the same width and colour as in the hyphal cords.

Subhymenial hyphae often somewhat sinuous, thin to thick-walled; forming a rather dense tissue. Individual hyphae (1.8-) 2.1-3.0 μm wide, with a mean width of 2.5 μm; hyaline to pale green in KOH, blue green in the presence of air; hyaline to pale blue green in water, with strongly granular contents.

Basidia with four slightly curved sterigmata, occasionally two-sterigmate; clavate to narrowly clavate, sometimes clavopedunculate, thin-walled, with one-three slight constrictions. Dimensions: (33-) 34-56 (-59) × (5.8-) 6.2-7.8 (7.9) μm; mean dimensions: 44 × 7.2 μm. Sterigmata 4.4-5.6 (-6.8) μm long, with a mean length of 5.1 μm. Colours and reactions the same as for the subhymenial hyphae, but in addition often with granular contents in KOH.

Cystidial organs lacking.

Basidiospores in frontal face generally with a subcircular basic shape and an angular to nodulose or sometimes star or cross-shaped outline, covered in bi- or trifurcate, sometimes singularly attached, echinuli. Nearly all spores with five distinct, square lobes, but depending on the precise angle sometimes perceived as three; four-lobed spores occasionally occurring; abnormally large spores originating from two-sterigmate basidia infrequently seen. Frontal dimensions: (6.1-) 6.2-7.0 (-7.1) × (5.8-) 6.3-7.2 (-7.3) μm; mean dimensions: 6.6 × 6.8 μm; Q-value: 0.9-1.0; mean Q-value: 1.0. Echinuli 0.6-0.9 (-1.1) μm long, with a mean length of 0.8 μm. Lateral face ellipsoid to ovoid, usually with evenly rounded edges, sometimes with one-three lobes. Lateral dimensions: 6.3-6.9 (-7.3) × (4.0-) 4.1-4.8 (-5.0) μm; mean dimensions: 6.5 × 4.4 μm; Q-value: (1.3-) 1.4-1.6; mean Q-value: 1.5. Colour in both KOH and water pale brownish-yellow to pale blue green; inamyloid.

Chlamydospores lacking.

Habitat.

The only specimen recorded to date of P. atrofusca is the type collection, which was collected on wood of Pinus ponderosa . Available UNITE sequences originate from root tips of Rhododendron decorum ( Kõljalg et al. 2005, Nilsson et al. 2019).

Distribution.

Basidiome encountered in: United States. Soil or root tip samples confirm presence also in: China.

Remarks.

Within the P. tristis group, the basidiome of P. atrofusca can be recognised by its hyphal cords and skeletal hyphae. These features make it unique within the group and the risk for confusion with any other described species should be small. Outside the P. tristis group, P. rhizopunctata is somewhat similar, but differs from P. atrofusca by the presence of chlamydospores on its hyphal cords.