With few exceptions, red clover is self-incompatible. Reciprocal crosses between 30 pairs of unrelated parents sampled in a population, were all compatible. Three full-sib F2's from one of these crosses showed, in 8 x 8 diallel crosses, 2, 2 and 4 incompatibility groups, and an F5 showed, in a 15 x 15 diallel cross, 2 incompatibility groups. The data were explained by a (large) series of S alleles, as proposed by East for Nicotiana and by Filzer for Veronica.In a number of progenies, male-sterility (degenerate anthers) was found and a recessive factor was identified.Seed-coat colour (yellow versus violet) was polymerically controlled (up to 5 cumulative factors), complicated by environmental and within-plant variation. In certain progenies a factor for violet (v) and an intensifier (X) could be identified. The quality of yellow and of violet was controlled by C-c and by R-r, respectively.Flower colour was determined by the factor G for anthocyanin production and by B-b for purple or pink, along with at least 3 intensifiers of purple.Two chlorophyll abnormalities depended on recessive factors (chlorina and albina) and one was plasmatically inherited (albomaculata). Two types of dwarfs (nanella and nana) were single recessives.