Variations in floral traits of sympatric alpine shrubs, Phyllodoce caerulea and Phyllodoce aleutica, along snowmelt gradients

Floral traits (corolla length, corolla shape, anther-stigma distance, and corolla color) of sympatric alpine shrubs, Phyllodoce caerulea and Phyllodoce aleutica, were compared among three populations having different snowmelt timing selected along snowmelt gradients (i. e., early-, middle-, and late-snowmelt population) at three snowbeds in the Taisetsu Mountains, northern Japan. The corolla of P. caerulea was longer and more oblong than that of P. aleutica. The anther-stigma distance of P. caerulea was longer than that of P. aleutica. These morphological differences suggest that flowers of P. caerulea are more suitable for outcrossing than those of P. aleutica. The anther-stigma distance of P. aleutica tended to increase in the late-snowmelt populations. This supports our previous results that P. aleutica increased outcrossing success but decreased selfing ability by autodeposition in late-snowmelt populations. The corolla color of both species varied considerably among populations within each snowbed, however, directional trends in changing patterns were not detected along the snowmelt gradients. Coefficients of variation in corolla length, corolla shape, and anther-stigma distance did not show any directional patterns along the snowmelt gradients in either species. Although clear directional trends in most floral traits were not detected along the snowmelt gradients, these traits were more variable among populations within each site than among sites in both species. Thus, differences in snowmelt timing may be an important factor maintaining genetic variations within a local area