Omphalia caesioatra Speg., An. Mus. Nac.

Honan, Amy H., Desjardin, Dennis E., Perry, Brian A., Horak, Egon & Baroni, Timothy J., 2015, Towards a better understanding of Tetrapyrgos (Basidiomycota, Agaricales): new species, type studies, and phylogenetic inferences, Phytotaxa 231 (2), pp. 101-132 : 130

Omphalia caesioatra Speg., An. Mus. Nac. Buenos Aires 6: 107. 1898

Synonym: Marasmiellus caesioater (Speg.) Singer, Rev. Mycol. 18: 9. 1953.

Accepted as a synonym of Tetrapyrgo s nigripes by Horak (1983, 1987).

Holotype:— ARGENTINA. Buenos Aires Prov.: La Plata , on stems and leaves of grass, April 1888, C Spegazzini 46 ( LPS 16794 !).

The holotype specimen consists of two fragmented basidiomes attached to the base of the stem of a grass, both entirely blackened and in poor condition. Description of dried holotype: Pileus 4 mm diam., convex. Lamellae badly eroded. Stipe 8 × 1 mm, non-insititious. No basidiospores observed; basidiospores reported as 10 × 5 μm, ellipsoid to ovoid ( Spegazzini 1898), or 8–13.8 × 4–6.8 μm, oblong to fusoid-ellipsoid ( Singer1973). Hymenial elements collapsed, not observable. Pileipellis a cutis of non-diverticulate hyphae 3.5–8 μm diam., smooth, with dark brown vacuolar pigments (necropigments?); walls hyaline, thin; no pileocystidia observed. Singer (1950: 188) reported the epicuticular hyphae as diverticulate.

Status: The non-diverticulate pileipellis hyphae in combination with black necropigments and fusoid-ellipsoid basidiospores indicate placement in Marasmiellus sect. Candidi , not in Marasmiellus sect. Tricolores as indicated by Singer (1973: 92), nor is the species a synonym of Tetrapyrgos nigripes as indicated by Horak (1983, 1987). Omphalia caesioater is phenetically similar to Marasmiellus subnigricans (Murr.) Singer , another blackening species.