The genome size and the base composition (GC%) of sight Hypochaeris species
were determined by flow cytometry in order to establish the pattern of nuc
lear DNA variation within the genus. The species analysed showed an almost
fivefold range of variation from 1.68 pg in H. cretensis to 8.10 pg in H. u
niflora. This variation in DNA content is greater between taxonomic section
s of Hypochaeris species than within a section. There was no correlation be
tween 2C DNA content and GC% indicating that neither the GC fraction nor th
e AT fraction were preferentially associated with variation in genome size.
Because there is little heterochromatin, these results show that it is int
erspersed repeated sequences that are most probably implicated in this vari
ation. From phylogenetic analysis, it is likely that genome size has evolve
d by loss of DNA content in some lineages and by gain in one lineage from a
n ancestral genome which was probably similar to genomes of intermediate si
ze in Hypochaeris.