I tested whether a region of high female frequencies in the gynodioecious plant, Nemophila menziesii, may be due to hybridization between regionally distributed populations with different corolla colours. I crossed plants in the greenhouse from populations with different corolla colours and found that hybrid crosses yielded higher frequencies of females than within-colour crosses. In the field, I found that populations with high female frequencies had intermediate mean corolla colours and higher variance in corolla colour, two traits suggesting hybridization. Nemophila menziesii has nuclear–cytoplasmic sex inheritance, thus if populations with different corolla colours are fixed for different male-sterile cytoplasms and matching nuclear restorer alleles, hybridization between populations with different corolla colour should yield high frequencies of females. Two populations that are all hermaphroditic in the field segregated females in hybrid crosses suggesting that field populations may contain sex ratio distorters but appear undistorted, a prediction of genomic conflict theory.