Habitat and reproductive isolation as factors in speciation between Liliumlongiflorum Thunb. and L-formosanum Wallace

We clarified the isolation status between Lilium longiflorum and L. formosa num which are endemic to the subtropical archipelago extended from the Ryuk yu Archipelago to Taiwan, From field observations of natural populations, c overing almost the entire native distribution of the species in their natur al habitats and recording their flowering times, stem leaf morphology, the three populations from the mainland and an islet of Taiwan and all those of the Ryukyu Archipelago were readily classified as L. longiflorum, whereas the remaining Taiwanese populations were grouped as L. formosanum. This ind icates that an interspecific isolation was never established by island sepa ration, but probably by the combination of relatively distinct differentiat ions in adaptability to their natural habitats and in flowering time. The e volutionary trends seem to have severely restricted the gene flow between t he species, and, thereby, promoted speciation.