Leaf Morphological Responses to Serpentine Soils in Shikoku, Japan: A Review of Common Patterns and Developmental Diversity

ABSTRACT Serpentine soil mosaics are found in Shikoku, Japan, and many plant species that inhabit these habitats change their morphology and anatomy in response to the soil chemical and physical properties. To clarify commonality and diversity in leaf morphological responses, we reviewed studies on phylogenetically distinct taxa occurring in serpentine areas, including the woody plants Eurya japonica Thunb. var. japonica (Ternstroemiaceae) and Ligustrum japonicum Thunb. (Oleaceae), and the herbaceous plants Adenophora triphylla (Thunb.) A.DC. var. japonica (Regel) H. Hara (Campanulaceae) and Aster hispidus Thunb. var. leptocladus (Makino) Okuyama (Asteraceae). Our review showed that the leaves of plants growing on serpentine soils tended to be smaller, suggesting that leaf growth may be inhibited under serpentine conditions. However, the developmental processes underlying this small‐leaf phenotype differed among taxa: leaf size reduction was associated with (i) reduced epidermal cell number in woody species, (ii) reduced epidermal cell size in Ad. triphylla var. japonica , and (iii) enlarged epidermal cell size in As. hispidus var. leptocladus . Moreover, the low water retention of serpentine soils was reflected in stomatal traits, since woody plants exhibited reduced stomatal size, whereas herbaceous plants exhibited changes in stomatal density. These findings suggest that leaf size reduction represents a common organ‐level response to serpentine environments, whereas the underlying cellular and stomatal responses are diverse among taxa. This review highlights the need for further comparative studies using standardized trait measurements to test whether these patterns represent general leaf syndromes across serpentine regions in Japan.