Saxifraga fortunei sensu lato (Saxifragaceae) varies greatly in morphology and includes many infraspecific taxa. As many as five varieties have been recognized in western Japan, although their discrimination based on leaf size or leaf shape, such as cuneate base or degree of lobing is often difficult to determine due to continuous variation. To quantify the variation in leaf morphology, especially focusing on cuneate and parted leaves, 259 samples from 87 populations in western Japan were subject to principal component analysis. Additionally, developmental changes in plants from three selected populations were examined. The findings revealed that plants with parted leaved (var. suwoensis) were discriminated from plants with cuneate and normal leaves, while plants with cuneate leaves (var. obtusocuneata) were within the range of variation of var. fortunei. Leaf shape changes from cuneate to truncate or cordate during the transition from a vegetative state to the flowering state. Cuneate forms usually occurred in sterile plants, but also on flowering plants even within a population. This characteristic was less useful for recognizing var. obtusocuneata. Populations with parted (long lobed) leaves as well as those with cuneate leaves usually grow along streams, confirming that phenotypes are the result of adaptive differentiation toward becoming facultative rheophytes, as previously suggested.
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