HIBRIDACION NATURAL ENTRE ESPECIES SUDAMERICANAS DE HYPOCHOERIS (ASTERACEAE)

H. chillensis (H.B.K.) Hieron. has a great morphological variability. It hybridizes in nature with two closely related species: H. megapotamica Cabr. and H. microcephala var. albiflora (O.K.) Cabr. The meiosis of the putative hybrids is regular except for the presence of univalents at a low frequency. Male gametes show low stainability. The hybrids have low seed production. The similar karyotypes, previously described by Saez (1951) and the absence of heteromorphic bivalents in the hybrids suggest the existence of cryptic structural hybridity, i.e. of small cryptic structural differences which are difficult to detect cytologically. It is also suggested that the great morphological variability of H. chillensis could be due to introgression of genes from the other two closely related species.