Irpiciporus prismaticus Regio, Westphalen & R.M. Silveira sp. nov. Figs.3, 4

Mycobank: MB 851237

Type:— BRAZIL. Rio Grande do Sul, São Francisco de Paula, FLONA, 12.03. 2022, 922 m, N.C. Regio NR28 (Holotype ICN!).

Etymology:— prismaticus (Lat.) refers to the prismatic crystals present in the context and teeth trama.

Diagnosis:— Irpiciporus prismaticus is characterized by the pileate to effused-reflexed basidiomes with hydnoid hymenophore and presence of prismatic crystals in the context and teeth trama.

Description:— Basidiomes annual, effused-reflexed to pileate, pilei projecting up to 4 cm and more than 0.5 mm thick, solitary or imbricate, fragile, white to cream when fresh and soft to corky pale yellowish when dried. Pileus surface azonate and smooth to slightly velutinous due to small and partially collapsed hyphae. Hymenophore hydnoid to irpicoid composed of narrowly conical to flattened teeth, usually scattered to agglutinated or fused at the base, 1.5–3.5 mm long. Margin is indistinct when fresh but sometimes curling inward upon drying and composed of smaller teeth. Context soft, up to 2 mm thick and distinctly duplex in pileate parts of the basidiomes, composed of a brownish and more compact layer near the hymenophore and a spongy white to cream upper layer.

Hyphal system monomitic. Clamps abundant and easily observed. Generative hyphae thin- to slightly thick-walled, weakly cyanophilous and more inflated in the context. Teeth composed of uniform fascicles of non-agglutinated hyphae, usually with fine incrustations, encompassed by hymenial layers. Teeth trama and inferior context layer filled with prismatic crystals. Teeth tips are composed of tortuous cystidioles and little differentiated hyphidia. Cystidia absent, but inconspicuous, cylindric to hyphoid, thin-walled cystidioles usually present. Basidia cylindric to narrowly clavate, 16.5–23 (24) × 5–6, hyaline, clamped at the base, tetraspored and occasionally with short and fattened stalks. Basidiospores smooth, slightly thick-walled, subglobose to broadly ellipsoid, sometimes irregularly shaped, 4.5–6.5 × 3.5–6 µm, Q = 1.13 (average of four specimens), usually uniguttulate and slightly to strongly cyanophilous, IKI-.

Ecology and Distribution:—Growing on dead wood trunks of unidentified trees. Known only from Rio Grande do Sul, southern Brazil.

Comments:—Prismatic crystals were observed in all studied specimens, especially in the lower layer of the context, and were also observed in mycelium cultures in Malt Extract Agar. Similar structures can be found in Cerrena spp., but are described for the first time in Irpiciporus. Due to its variable morphology, I. prismaticus resembles I. mollis and I. pachyodon, differing in the hydnoid hymenophore, even in marginal areas of the basidiomes, and smaller basidia (30–40 µm long in I. mollis and I. pachyodon). Phylogenetically, it is closely related to I. branchiformis and I. sinuosus, but the former is registered only from Eastern Africa and has slightly smaller basdiospores, and the latter is clearly differentiated by its poroid hymenophore.

Irpiciporus rajchenbergii, recently described from nearby areas, presents similar prismatic crystals in the subiculum and basidiospore size (5–6 × (3.5–)4–5(–6) µm), but differs by the strictly resupinate basidiomes, slender and longer teeth (3–6.5 mm long) and considerably larger basidia (25–40 µm long). In contrast, I. revolubilis share similar basidia size, but the species is currently known only from its type locality in Venezuela, and differs by the resupinate and thinner basidiomes and the smaller basidiospores (4–5 × 3.6–4.3 µm).

Additional specimens examined:— BRAZIL. Rio Grande do Sul, Farroupilha, Parque dos Pinheiros, 21 January 2023, elev. 738 m, M.C. Westphalen 738/23 (ICN); São Francisco de Paula, FLONA, 06 August 2022, elev. 922 m, N.C. Regio NR49 (ICN); CPCN Pró-Mata, 20 April 2023, elev. 900 m, N.C. Regio NR115 (ICN).