Infrageneric relationships of Lipochaeta were assessed by way
of a controlled crossing program that produced 14 intrasectional and 5
intersectional hybrid combinations involving the two sections Aphanopappus
and Lipochaeta. Results from uniform culture and hybridization studies
confirm that specific differences involving many traits such as leaf shape, the
number of disk floret lobes, and achene morphology have a genetic basis.
Fertility data based on pollen stainability and achene set of some of the
hybrids revealed that members of the same section are highly interfertile,
whereas the two sections are extremely well isolated from each other reproductively.
Cytogenetic evidence suggests that this isolation is due primarily to
a difference in the ploidy level of the two sections and that section Lipochaeta,
with n = 26, has an allopolyploid origin from a IS-paired taxon similar to a
diploid Lipochaeta and an unknown II-paired taxon in the extra-Hawaiian
genus Wedelia. Chromosome counts for three diploid species and one tetraploid
variety are reported for the first time
