The diploid chromosome number of 2n=l8 was recorded in plants from 16 accessions of Brachiaria ruziziensis Germain et Evrard. Meiosis appeared regular and pollen stainability averaged 87%. The female gametophyte was derived from a megaspore and when mature had eight nuclei. Cross‐fertilization occurred at a very high frequency under conditions of natural open‐pollination. Seed set averaged 21 and 0.4% for open‐ and self‐pollination, respectively, suggesting the operation of a self‐incompatibility mechanism. One generation of self‐fertilization reduced seedling germination and survival. Significant inbreeding depression for total dry matter production was found in 4 of 6 S, families.