Life-history in some cases very complex and with well-marked sexual process and alternation of generations, in others much reduced; basidium (promycelium) derived usually from a thick-walled spore (teleutospore).
The teleutospore puts forth on germination a fourcelled structure, the promycelium or basidium, and this bears later four sporidia or basidiospores, one on each cell.
Formerly, before the relationship of promycelium and basidium were understood, the Uredineae were considered as quite independent of the Basidiomycetes.
The first named contains a small number of forms with the basidium divided like the promycelium of the Uredineae.