Population differentiation in the leaf shape and growth form of Cardamine scutata Thunb. in tidal and non‐tidal habitats

Abstract

AbstractRiparian habitats are associated with diverse hydrological conditions that may enhance population differentiation in species inhabiting areas close to water. Cardamine scutata Thunb. is a widespread riparian herb that is typically characterized by compound leaves. On the Nohbi Plain in central Honshu, Japan, it has, however, been reported that plants of C. scutata occurring in tidal wetlands along the lower reaches of large rivers have simpler leaves than those inhabiting areas further upstream. In this study, we quantitatively describe environmental conditions, leaf shape and other phenotypic traits of populations in tidal and non‐tidal habitats. Measurements of the electrical conductivity of interstitial water and fluctuations in water levels indicated that tidal populations of C. scutata occurred in typical tidal freshwater wetlands. We found that tidal and non‐tidal populations are characterized by distinct leaf shapes, simple and compound, respectively, under both field and common growth conditions. These observations indicate that differences in leaf shape reflect a genetic differentiation between populations of the same species inhabiting distinct habitats. In addition to leaf shape, we found several phenotypic differences relating to growth form, with plants in tidal populations having elongated hollowed stems and elongated inflorescences. We conclude that tidal populations of C. scutata are a discrete ecotype inhabiting freshwater tidal wetlands, presumably derived either through adaptation or genetic drift.