Summary:
Tetragoniomyces uliginosus is tiny and not likely to be encountered, but is included for its intrinsic interest. It has thick-walled 4-celled basidia that fall off and germinate directly without a basidiospore stage. The deciduous basidia may well be an adaptation for water dispersal.

Microscopic:
basidiospores absent; mature basidia 10-12(15) x 7-10 microns, "deciduous, rhomboidal in outline, the 4 cells occupying a single plane", "germination by direct outgrowth of dikaryotic hyphae or by the formation of germ tubes which conjugate outside the basidium and initiate development of dikaryotic hyphae"; probasidia at first ellipsoid to globose [spherical] or pyriform [pear-shaped], thin-walled when first produced, becoming thick-walled before division, 4-celled at maturity, walls of the compartments also becoming secondarily thickened, the cells rounding off and becoming almost spherical, "held together by the sculptured, closely appressed outer wall"; basidia "borne terminally on branched basidiophores, the latter elongating slightly before producing each basidium, the clamp vestiges remaining on the basidiophore"; hyphae narrow, 2-5 microns in diameter, with clamp connections, "attached to the inflated host cells by haustoria"

Notes:
T. uliginosus is found at least in BC, Finland, and Germany.