Tetrapyrgos subdendrophora (Redhead) E. Horak, Sydowia 39: 103. 1987 [1986]. Fig. 7a–h

Basionym: Campanella subdendrophora Redhead, Mycologia 66: 185. 1974.

Synonym: Pterospora subdendrophora (Redhead) E. Horak, Sydowia 36: 137. 1983.

Holotype:— CANADA. British Columbia: University of British Columbia Endowment Lands, on Phalaris arundinacea, 15 September 1972, leg. SA Redhead (DAOM 145301!).

The holotype specimen consists of numerous grass stems glued to the inside of the lid of a specimen box, with>10 tiny fragmented basidiomes attached to substrate, and several loose fragmented basidiomes in a packet.

Description of dried holotype: Pileus convex, cleft; surface wrinkled, pallid cream. Lamellae poorly developed, forked, narrow, cream. Stipe well-developed, eccentric, passing through cleft in pileus, cylindrical, curved; surface pruinose, pallid.

Description based on newly collected specimens: Pileus 2–10 (–22) mm diam., in side view hemispherical or convex when young, becoming irregular to plano-convex in age; in face view chordate to rounded or irregularly chordate; rugulose to rugulo-sulcate; surface dull, dry, opaque to subtranslucent, minutely pruinose or felted overall, white through development, staining greyish brown to bluish grey or olivaceous. Context in pileus thin (<0.5 mm), rubbery-gelatinous, pliant, concolorous. Lamellae shallowly adnate to adnexed, distant, with 1–2 series of lamellulae, strongly anastomosing and intervenose, edges pruinose, white, staining concolorous with pileus in age. Stipe 0.5–3 × 0.5–1 mm, eccentric to strongly eccentric, appearing lateral in side view, arising through the cleft in pileus, even or slightly tapered downward, solid, white at very apex, base black to blue black, white-pruinose overall, arising from a black basal disc. Odor and taste not distinctive.

Basidiospores (6.4–) 8–12 × (4.8–) 5.6–10.4 μm [x mr = 8.4–10.2 × 6.5–7.7 μm, x mm = 9.5 ± 0.62 × 7.2 ± 0.48 μm, Q = 1–1.9, Q mr = 1.2–1.5, Q mm = 1.3 ± 0.12, n = 20, s = 13], triangular to shallowly tetrahedral, often with a large vacuole, hyaline, inamyloid, thin-walled. Basidia 36–45 × 3.2–8 μm, clavate, 4-spored, hyaline, inamyloid, thin-walled, clamped. Basidioles 28–38 × 4–7 μm, clavate to fusoid, hyaline, inamyloid, thin-walled. Hymenial cystidia common on lamellar sides and edges, 40–64 × 3.2–9.5 μm, irregularly cylindrical; apex capitate 6.5–9.5 diam, hyaline, inamyloid, thin-walled to firm-walled (–0.7 μm), ranging from non-diverticulate to somewhat densely diverticulate on the central axis, pedicellate, rarely entirely diverticulate; diverticula 0.8–4 (–8.8) × 0.8–2.4 (–4.8) μm, cylindrical or knob-like, occasionally branched. Pileipellis a Rameales -structure of loosely interwoven diverticulate hyphae with suberect to erect terminal cells; terminal cells 35–53 × 3–8 μm, irregularly cylindrical, densely diverticulate below a clavate to bulbous capitulum, 5.5–8 μm diam; apex occasionally thick-walled, hyaline, inamyloid, thin-walled; diverticula 0.8–4 × 0.8–3.2 μm, cylindrical to knob-like, occasionally conical or branched. Pileus trama weakly gelatinized. Lamellar trama interwoven; hyphae cylindrical, smooth, gelatinized. Stipitipellis similar to the pileipellis. Clamp connections present.

Habitat and known distribution: On monocotyledonous leaves and stems of Carex spp. (Cyperaceae), Phalaris arundinacea (Poaceae) and various other grasses, and rarely on dicotyledonous stems (Rubus) and twigs (Baccharis). Western North America.

Material examined:— CANADA. British Columbia: University of British Columbia Endowment Lands, 15 September 1972, leg. SA Redhead (DAOM 145301, Holotype). UNITED STATES. California: Mendocino County, Jackson State Forest, road to Mendocino Woodland Camp off Hwy 408, AH Honan 149 (SFSU); San Mateo County, Junipero Serra Park, December 2004, AH Honan 78, AH Honan 79 (SFSU); same location, 22 February 2005, AH Honan 119 (SFSU); same location, 5 March 2005, AH Honan 120 (SFSU); San Mateo County, Montara State Beach, McNee Ranch, beginning of trail to Montara Mountain, 12 November, 2005, AH Honan 148 (SFSU); Solano County, near Monticello Dam, along banks of Putah Creek, 29 January 2005, AH Honan 118 (SFSU); Sonoma County, Salt Point State Park, Woodside Campground, 11 November 2001, DE Desjardin 7338 (SFSU). Oregon: Coos County, Bullard’s Beach, 25 November 2005, AH Honan 152 (SFSU).

Commentary: Based on morphological and molecular data, T. subdendrophora and T. olivaceonigra are sister taxa, differing subtly in basidiome pigmentation. Tetrapyrgos subdendrophora is distinguished by a small white pileus, strongly intervenose-anastomosing lamellae, the reduced and eccentric stipe, slightly gelatinized tramal tissues, and sparsely centrally diverticulate, capitate cheilocystidia. Interestingly, T. subdendrophora fruits on both monocotyledonous (members of the Cyperaceae and Poaceae) and rarely on dicotyledonous (Baccharis, Rubus) substrates. Redhead (1974) provided black and white photographs of basidiomes on grass culms, and a map referencing specimens from western Canada and Oregon (Redhead 1989). Desjardin et al. (2015) published a color photograph of basidiomes from California. Tetrapyrgos subdendrophora is morphologically similar also to T. reducta and T. tropicalis, differing by the features outlined in the key.