Lamelloclavaria petersenii Adamčík & Birkebak, in Birkebak et al., Mycologia 108(5): 862 (2016)
Etymology: Generic name in reference to the phylogenetic relatedness to the genus Clavaria but distinct in producing lamellae. Specific epithet in honor of Dr Ronald H. Petersen and his contributions to fungal systematics, taxonomy, and evolution of basidiome morphology, particularly with respect to the Clavariaceae sensu lato.
Pileus 8–15 mm diam, initially convex, later nearly plane, rarely slightly depressed, often with a small papilla on the disc; margin involute when young, becoming straight, nonstriate; surface non-hygrophanous, dry, finely rimulose; color hair brown (5E4), sepia brown (5F4), dark blond (5D3) to nougat brown (5D3), more or less uniformly colored. Stipe 16–20 mm long 6 1–2 mm diam, cylindrical, sometimes eccentric, smooth and shiney, finely granulose near the extreme apex, concolorous with the pileus, base sometimes white tomentose. Lamellae 18–24, lamellulae 1–3, entirely adnate to slightly decurrent, edges entire; birch gray (5C2), dust gray (5D2) or drab (5E3); relatively thin. Context compact and elastic, pale grayish, becoming black, especially near and on the surface when dry; taste mild, lacking a distinctive odor. Spore deposit not observed.
Basidiospores (5.0–)5.2–5.9(–6.2) x (2.5–)2.7–2.9 (–3.0) μm, av. 5.5 x 2.8 μm, Q = (1.83–) 1.88–2.14 (–2.35), av. Q = 2.01, phaseoliform to oblong, sometimes with a central constriction, hyaline, smooth, inamyloid, not dextrinoid, usually with one large vacuole, thin-walled, hilar appendage 0.4–0.6 μm long. Basidia 4-spored, 22–26.5(–28) x 5–6 μm, av. 24.5 x 5.5 μm, hyaline, clavate, attenuated and flexuous toward base. Basidioles cylindrical to narrowly clavate, often flexuous, 2–4.5 μm diam. Hymenium without cystidia, lamellae edge fertile. Subhymenium sharply delimited from parallel hyphae of lamellar trama, pseudoparenchymatic, ca. 10–15 μm deep, trama of the lamellae composed of parallel, ca. 3–10 μm diam, hyphae that are often anastomosed and sparsely branched, often with very short cells (ca. 10–25 μm), but sometimes also longer (50–100 μm long). Pileipellis near margin of the pileus a cutis, composed of relatively thin layer of relatively numerous, repent hyphal terminations with pale brownish intracellular pigment, terminal cells frequently larger, ventricose, fusiform, broadly clavate to lageniform, occasionally narrow cylindrical, occasionally with irregular nodules, (6–)13.5–43(–78) x (3–)4.5–10(–13.5) μm, av. 28.4 x 7.5 μm; basal cells usually shorter and sometimes intermingled with very short (shorter than 10 mm) cells, with or without constrictions at the septa, usually forming chains of 2–4 (or more) unbranched cells; subpellis and trama of the pileus of ca. 5–12 μm diam, parallel, hyaline hyphae, that are very variable in length, usually shorter than 50 μm and intermingled with very short (up to 10 μm) elements, often anastomosed, scarcely branched. Hyphal terminations near center of the pileus, also a cutis, but of more dispersed and shorter hyphae, some composed of a single cell or lateral branch without a septum arising from horizontally oriented hyphae, with terminal cells more irregular and often nodulose, (13.5–)25.5–51(–66) x (2–)4–8(–10) μm, av. 38.2 x 5.9 μm, occasionally with intracellular crystals observed in Congo red. Caulocystidia dispersed or in small clusters, thin-walled, repent or ascending, with terminal cells measuring (14–)25–56(–69) x 2.5–4.5(–9) μm, av. 40.4 x 3.5 μm, typically narrow, moniliform and often flexuous, obtuse to slightly constricted near the apex, mostly cylindrical to narrowly clavate, with pale brownish intracellular pigments and occasionally with dispersed crystals visible in Congo red. Trama of stipe of comparatively wider hyphae than caulocystidia, often thick walled, but otherwise similar to those in the pileus trama. Clamp connections absent in all tissues.
Index fungorum number: IF810135
Notes: The designation of the genus Lamelloclavaria is based on the new species L. petersenii, which is based on a single collection from Finland. The combination of the broadly adnate to decurrent lamellae, likely white spore print, finely rimulose gray cap with a small papilla, absence of clamp connections on hyphae and phaseoliform to oblong, small basidiospores makes this species striking in the field and under the microscope. This genus is not treated in recent keys to agaricoid fungi occurring in Nordic countries (Knudsen and Vesterholt 2012), and despite the effort of the authors and other mycologists, it has not been re-collected during the last ten years. It would appear that it is an extremely rare but conspicuous species. The genus is easily distinguished from other members of the Clavariaceae by its filamentous pileipellis (with repent dispersed hyphal terminations) and basidiospore shape. The combination of the rimose pileus surface, small stature, occurrence on ground and phylogenetic placement differentiate it from lamellate species in the Hygrophoraceae.
Figure 1. Lamelloclavaria petersenii (agaricoid, photograph by Stefan Jacobsson).
Figure 2. Lamelloclavaria petersenii (holotype). A. Hyphal terminations in pileipellis near the pileus disc. B. Hyphal terminations in pileipellis near the pileus margin. C. Caulocystidia. D. Basidia. E. Basidioles. F. Basidiospores. Scale bar = 10 μm; 5 μm for basidiospores.
Birkebak, J. M., Adamčík, S., Looney, B. P., & Matheny, P. B. 2016. Multilocus phylogenetic reconstruction of the Clavariaceae (Agaricales) reveals polyphyly of agaricoid members. Mycologia, 108(5), 860–868. doi:10.3852/15-370