Infrageneric Relationships and the Origin of the Hawaiian Endemic Genus Lipochaeta (Compositae)

Abstract

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.