Plants along rivers have narrow leaves to avoid the stress caused by the river’s flow during flooding. Plants that have undergone such morphological leaf modifications to adapt to rivers are called rheophytes. Some populations of Eurya japonica Thunb. (Ternstroemiaceae) were grown on riversides so that the comparative morphology and anatomy of leaves between riverside and inland (control) populations could be examined to confirm their rheophytic speciation. Our morphological and anatomical analyses revealed that the leaf of E. japonica in the riverside populations was significantly smaller than that of the inland populations due to the decreased number of cells; therefore, the pattern of rheophytic differentiation in riversides was not the stenophyllization but the miniaturization of the leaf. Moreover, our results indicated that this species in the riverside populations had thicker leaves and higher density of stomata than those of inland populations, suggesting that E. japonica had been morphologically modified in response to the light and water environments along the river.

Serpentine soils are known to affect plant growth and plants in these soils have morphological and anatomical modifications. Comparative leaf morphology and anatomy studies of Eurya japonica Thunb. was conducted between serpentine and inland (control) areas. Our morphological analyses revealed that the individuals in the serpentine areas had significantly smaller and thicker leaves than those in the inland areas. Our anatomical analyses showed that the smaller leaves of serpentines had decreased numbers of cells, and their thicker leaves contributed to the increased height of epidermal cells, palisade tissue, and spongy tissue. Furthermore, the stomatal size of serpentines was significantly smaller than those from the inland areas. We concluded that E. japonica adapted to the serpentine areas by decreasing leaf size due to low levels of nutrients, by thickening the leaves to store water and reducing the stomatal size to minimize water loss via gas exchange.