Small agaric, growing in litter or mulch or on wood, with a white or cream to yellow spore print. Pileus white, pale, brown, rarely green or blue, not viscid. Lamellae adnate, subdecurrent or with a decurrent tooth or decurrent. Stipe central. Partial veil remnants absent. Spores cross-shaped or tetrahedral with two to five large projecting nodules, hyaline, non-amyloid, smooth; germ pore absent. Cheilocystidia present. Lamellar trama regular or interwoven. Pileipellis a cutis or a trichoderm. Clamp connections present.

Very similar in appearance to some smaller species of Gymnopus (many of which were formerly placed in Marasmiellus) but distinctive because of the nodulose spores. The general aspect of the fruit-body, including the dark stipe base, is similar to that of some species of Marasmius, but those have a hymeniform pileipellis, and the spores are not nodulose. The other Australian species of Tetrapyrgos (T. olivaceonigra) has an excentric or lateral stipe.

One species: Tetrapyrgos nigripes (= Marasmiellus, = Cantharellus nigripides).

Tetrapyrgos olivaceonigra, with a lateral stipe, is keyed out separately.

Tetrapyrgos nigripes (Schwein.) E. Horak, Sydowia 39: 102 (1987).

N.S.W. (and possibly also N.T., Qld and Vic.).

In native forests.

On litter or wood.

Saprotrophic.

Eyssartier, G. & Buyck, B. (2001), Notes on the Australian species described in the genus Cantharellus (Basidiomycetes), Austral. Syst. Bot. 14: 587–598. [Microcharacters of T. nigripes (as Marasmiellus nigripes, with synonym Cantharellus nigripides)]

Horak, E. (1983b), Neufunde und Bemerkungen zu einem emendierten Gattungskonzept von Pterospora Métrod (Agaricales), Sydowia 36: 125–138. [Description, B&W Illustration and Microcharacters of T. nigripes (as Peterospora), with key to genus Pterospora including similar species to T. nigripes such as P. atrocyanea]

Pegler, D.N. (1977), A preliminary agaric flora of East Africa, Kew Bull., Addit. Ser. 6: 1–615. [Description, B&W Illustration and Microcharacters of T. nigripes (as Marasmiellus subcinereus, see also Horak (1983b) for discussion of identity)]

Singer, R. (1973), The genera Marasmiellus, Crepidotus and Simocybe in the Neotropics, Beih. Nova Hedwigia 44: 1–517. [Description and Microcharacters of T. nigripes (as Marasmiellus)]

Singer, R. (1975), The neotropical species of Campanella and Aphyllotus with notes on some species of Marasmiellus, Nova Hedwiga 26: 847–895. [Description, sketchy B&W Illustration and Microcharacters of T. nigripes (as Marasmiellus)]