GENETIC AND CYTOLOGICAL INVESTIGATIONS IN SEXUAL ERIGERON COMPOSITUS (ASTERACEAE)

Erigeron compositus is an agamospermous species complex comprising sex ual and agamospermous elements. Five subspecies were informally propos ed by Beaman for sexual E. compositus: ''anticus,'' ''compositus,'' '' pectinipetiolatus,'' ''penicillatus,'' and ''posticus.'' Chromosome co unts reported herein show that sexual E. compositus is predominantly d iploid, 2n = 18. Sexual tetraploids, 2n = 36, and an aneuploid, 2n = 3 5, were also observed. Genetic Variation was examined in all of the pr oposed subspecies, with the exception of E. compositus ''anticus,'' an d in closely related E. vagus. The four proposed subspecies investigat ed are allozymically very similar with a mean genetic identity value ( I) of 0.847. Likewise, comparisons between populations of E. vagus and E. compositus yield an I value of 0.889. Fixation indices derived fro m allozyme data also show that sexual E. compositus and E. vagus are s trongly outcrossing. Allozyme markers, genetic similarity values, and patterns of morphological variation suggest that sexual tetraploid E. compositus is derived from a cross between diploid E. compositus ''com positus'' and one or more other sexual ''subspecies'' of E. compositus . These results represent the first phase in the chromosomal and genet ic analysis of the E. compositus agamospermous complex.