Cytogenetic investigations onOenothera nutans (Onagraceae)

Oenothera nutans, common to the Appalachian Mts between 650 and 1 700 m altitude, was investigated cytogenetically and taxonomically. The species is permanently structurally heterozygous. It consists of two genomes of the B-type which are more or less indistinguishable phenotypically. Nearly all of the strains investigated possess a self-incompatibility factor in one of the two complexes. Both complexes show a close relationship to the predominantly homozygousO. grandiflora, a native of the southern lowlands.O. nutans andO. grandiflora possess the same plastid type, plastome III. Probably,O. nutans evolved by an accumulation of reciprocal translocations within an originally structurally homozygous population, which must be regarded ancestral to the present forms ofO. grandiflora.