Arthromyces claviformis

Arthromyces claviformis T.J. Baroni & Lodge 2007, in Baroni et al., Mycological Research, 111(5): 574 (2007).

Etymology: claviformis, shape of a nail.

Diagnosis: Pileus white or pale ashy gray at first from floccose, felty tomentose/fibrillose or matted hyphal mat overall, soon dark olivaceous fuscous (5F4-5 Sepia - Soot Brown) from powdery conidia progressively developing from center to margin, 3-15 mm broad, convex or plano-convex and broadly depressed or on some very sharply and deeply depressed, with strongly inrolled margin. Flesh fuscous-watery or dark grayish, approx. 1 mm thick. Lamellae sordid white or pale cream, with pale golden, greenish golden or chartruese granulate edge (use lens), dark golden or golden-brown granulate as dried, adnate, emarginate or somewhat sinuate, crowded, very narrow when young, moderately broad with age (approx. 0.5-1 mm), edge serrate or mostly eroded, finely fimbriate. Stipe concolor with pileus, white mycelioid over base, densely white floccose-fibrillose then soon in development densely olivaceous-fuscous powdery over the fibrils, 2-5 mm broad at apex, 15-50(-70) mm long, mostly equal but often with a stongly tapered, rooting base, vestiture on stipe perpendicular erect and white with olive-fuscous tips, approx. 1 mm thick covering apex to near base, but not over base, dark grayish stuffed, becoming narrowly to moderately hollow. Odor musty or not distinctive. Taste not noted.

Basidiospores white in deposit, 4.4-6.6 x 3.1-3.9 µm (n/4 = 53, mean = 5.5 ± 0.41 x 3.5 ± 0.21, Q = 1.29-1.90, Qm = 1.59 ± 0.14), ellipsoid or ovoid or somewhat pip-shaped, round in polar view, hyaline, inamyloid, not dextrinoid, walls cyanophilic, smooth. Basidia 4-sterigmate, narrowly clavate, , 13.8-17.8 x 4.8-5.6 µm, with cyanophilic (= siderophilic) bodies. Cheilocystidia narrowly clavate or cylindrical, some subcapitate, 33-63 x 4-5 µm, in densely packed clusters forming a sterile edge, pale golden or dark golden in 3% KOH, individual cells hyaline with thin, resinous, golden coating or exudate in an even or disrupted coating over apices. Pleurocystidia absent. Lamella trama hyaline, of parallel, inflated hyphae, 6-14 µm in diam. Pileus context radially arranged, hyaline near the surface, pale brownish deeper in context from yellowish brown encrusted and intraparietal pigments of the thickened walls, of mostly inflated hyphae, 4-21 µm in diam. Pileipellis a loosely entangled or erect layer (± trichodermial) or in places collapsed, of hyaline cylindrical, non-encrusted hyphae, 2.4-4 µm in diam, producing from the erect hyphal tips with age, dark brown pigmented chains of arthroconidia that easily disarticulate into individual cells. Arthroconidia mostly rectangular or many ellipsoid with rounded corners, some ± globose, occasionally branched, some curved, occasionally also remaining in pairs (with septa between two cells), 5.6-11.3 x 3.2-4.8 µm, thick-walled, brown from intraparietal pigment and finely brown verrucose roughened. Stipitipellis similar in construction to pileipellis, with a hyaline ± trichodermial layer producing dense masses of dark brown ornamented arthroconidia. Clamp connections none.

Index Fungorum Number: IF510712

Figure 1. Arthromyces claviformis (all from T. J. Baroni 8995, holotype). (A) Basidiomata, scale bar=10 mm. (B) Basidiospores. (C) Arthroconidia. (D) Pileipellis. (E) Cheilocystidia. Bars (B–E)=10 mm.