Genetic analysis of isozyme segregation patterns inLayia(Compositae) showed that cytosolic phosphoglucomutase isozymes are encoded by duplicated genes, and that the cytosolic NADP‐dependent isocitrate dehydrogenase isozymes are encoded by duplicated genes in species with haploid chromosome numbers ofn =7 and triplicated genes in those withn= 8. The duplicated genes specifying both isozymes assorted independently in all species tested. An electrophoretic survey of phosphoglucomutase in diploid species representing six additional genera of Madiinae, the subtribe to whichLayiais assigned, revealed thatAchyrachaena, Calycadenia, Hemizonia, Holocarpha, andMadiaall possessed duplicated genes. InLagophylla, one species also had duplicated genes for the isozyme but a second species did not, a loss probably resulting from mutation or chromosomal deletion. The phosphoglucomutase duplication characterizes nearly the entire subtribe and may prove useful to identify phylogenetic relationships between the Madiinae and other subtribes.