The 29 spore-ball-forming smut fungus genera (of the total 58 recognized
genera) are analysed, grouped, briefly characterized and
illustrated. Problems within the genera, similarities, possible relationships
and differences between genera are discussed. The
following groups and genera are treated: genera with spores in pairs
(Schizonella, Mycosyrinx, Geminago), genera
with permanent
spore balls composed of colourless spores and sterile cells and/or
modified mycelia (Burrillia, Doassansia, Doassansiopsis,
Heterodoassansia, Nannfeldtiomyces, Narasimhania,
Pseudodoassansia, Tracya), genera with permanent spore
balls composed of pigmented
spores and sterile cells (Urocystis, Moesziomyces,
Dermatosorus, Testicularia), and genera with spore balls
containing only spores and
lacking sterile cells between the spore balls. Within the latter group,
the
two sub-groups were distinguished: one with light,
brownish spores (Sorosporium, Thecaphora, Glomosporium,
Fulvisporium), and another one with dark, blackish spores (Tolyposporium,
Tolyposporella, Clintamra, Orphanomyces).
Heterotolyposporium has small, hyaline spores between the pigmented
spore balls. Sporisorium and Macalpinomyces have
sterile cells between the true or pseudo spore balls. Odd genera are:
Ustacystis, Mundkurella and Uleiella. A
key to the spore-ball-forming genera of smut fungi is given. The value
of the spore balls in the taxonomy of the Ustilaginales is
discussed. The arrangement of the genera in groups is based on the
most important characters of the spore balls. It has a practical,
didactic purpose and in many cases the groups do not reflect natural relationships.