Recovery of a sexual and an apomictic hybrid from crosses between the facultative apomicts Hieracium caespitosum and H-praealtum

Hybridisation is a rare event in facultatively apomictic species. We report the recovery of two hybrids from reciprocal crosses between the facultativ ely apomictic species Hieracium praealtum and H. caespitosum. Both parents were tetraploid (2n=4x=36). H. caespitosum x H. praealtum (CR6) was a hexap loid (2n=6x=54) and an apomict. The increased ploidy number is evidence of a BIII hybrid origin, having arisen from the fusion of a reduced and an unr educed gamete. In contrast, the hybrid recovered from the reciprocal cross H. praealtum x H. caespitosum (RC4) was a tetraploid and therefore probably arose as a BII hybrid fi-em the fusion of two reduced gametes. Further evi dence for this is the expression of sexuality in this plant. As apomixis in Hieracium is thought to be determined by a single dominant locus, a sexual plant is consistent with a model of inheritance where this represents the putative homozygous recessive phenotype. The formation of a sexual plant fr om the hybridisation of apomicts has potentially significant evolutionary i mplications. The formation of an interspecific BIII hybrid has not previous ly been recorded.