Steccherinum undulatum Westphalen & R. M. Silveira 2026, sp. nov.

Steccherinum undulatum Westphalen & R. M. Silveira sp. nov. Figs 8 G, 9 G, 10 B, 11 I Etymology. Refers to the basidiomes with small, wavy pilei. Diagnosis. Recognized mainly by the combination of basidiomes formed by several small, wavy, imbricate pilei, aculei with 0.75–1 mm long, and ellipsoid basidiospores 3.3–4.1 × 2.0–2.7 (– 2.8) µm. Typification. Brazil. Rio Grande do Sul: São Francisco de Paula, CPCN Pró-Mata, 20 Apr. 2023, M. C. Westphalen 743 / 23 (ICN 213872). Description. Basidiomes adnate, concrescent, effused-reflexed, with several small, wavy, imbricate pilei, formed by the coalescence of several small pilei with conjoined reflexed bases, usually not detaching when dried, but easily separable if pulled from the substratum, somewhat membranaceous and pliable when fresh, turning papery to corky upon drying and somewhat waxy; pilei small, up to 4 mm wide and 9 mm in length, pilear surface cream to beige, tomentose, sulcate, and sometimes faintly zonate; sterile margins entire, somewhat cottony, smooth to finely fimbriate, up to 1.5 mm wide. Hymenophore hydnoid, at first orange in young and fresh specimens, then turning pale salmon to beige with age and upon drying, aculei 0.75–1.0 × 0.2–0.4 mm, with acute to round apices, sometimes slightly asperulate from the protruding cystidia, solitary or more rarely laterally fused, crowded, 4–6 per mm. Subiculum white, homogeneous, up to 0.6 mm thick. Hyphal system dimitic, subicular hyphae compact, not agglutinated, tramal hyphae parallel, intertwined, and densely arranged; generative hyphae clamped, thin to slightly thick-walled, hyaline, occasionally branched, 2–4 µm wide; skeletal hyphae thick-walled to almost solid, abundant throughout the basidiome, hyaline, 2–5 µm wide. Skeletocystidia abundant, immersed in the trama or with the apices protruding into the hymenium, covered with a thick cap of small crystals, 20–60 × 7–10 µm; leptocystidia present, often scattered and somewhat inconspicuous, mostly clavate or with a rounded apex, smooth. Basidia clavate, tetrasterigmate, 12–16 × 4–5 µm. Basidiospores ellipsoid, hyaline, thin-walled, IKI-, CB-, 3.3–4.1 × 2.0–2.7 (– 2.8) µm. Habitat and distribution. Known only from Araucaria forests in southern Brazil. Specimens examined. Brazil • Rio Grande do Sul: Canela, FLONA, 13 Jul. 2024, M. C. Westphalen 760 / 24 (ICN 213873). Notes. This species can be distinguished by its basidiomes consisting of small, wavy, imbricate pilei (Fig. 10 B). One of the collections studied (760 / 24) exhibited a bright orange coloration when fresh, whereas the other (743 / 23) displayed a more faded salmon hue. This suggests that only young, fresh specimens display brighter colors, which gradually turn paler as they mature or dry. The aculei of S. undulatum are the second largest in the group, being smaller only than those of S. subochraceum. Microscopically, the species also features slightly larger basidiospores when compared to S. molle, S. resinaceum, and S. bononiae, but smaller than those of S. elegantissimum. Although surveys for Steccherinum species have been ongoing since 2017, only two specimens of S. undulatum have been found, both in Araucaria forests in southern Brazil, approximately 45 km apart. This suggests that it is likely rarer than other species in the group, which have been more frequently collected and are more widely distributed.