NUCLEAR DNA CONTENT VARIATION IN HELIANTHUS (ASTERACEAE)

Nuclear 2C DNA content was microspectrophotometrically determined for 19 diploid (2n=34) species of Helianthus L. DNA amount varied over a fourfold range. Helianthus neglectus had the lowest (53.40 ± 0.51 Feulgen absorbancy units [FAU]) and H. agrestis the highest (216.30 ± 2.30 FAU) DNA content. Chromosome size ranged from 1.1–1.7 μm long in H. neglectus to 3.2-5.0 μm long in H. agrestis. When the highly divergent H. agrestis was excluded from analyses, the mean of the annual species (70.05 FAU) was significantly different from the mean of the perennials (97.70 FAU). No correlations of DNA content with habitat, soil type, annual precipitation, or geographical location were apparent among species.