In evergreen azalea, unique old mutational cultivars, whose flower have split figure, have been collected and is called “sai-zaki” in Japanese. The morphology of leaves and flowers of the wild-type and sai-zaki cultivars ‘Hanaguruma’, ‘Gin-no-zai’, and ‘Seigaiha’ of R. macrosepalum was investigated. In contrast to the gamopetalous corolla of the wild type, all sai-zaki cultivars formed the choripetalous corolla type, which consisted of 5 independent petals. The width of the leaf, sepal, and petal of all sai-zaki cultivars, except for the sepal of ‘Gin-no-zai’, all tended to be narrower than the wild type; in particular, all lateral organs of ‘Seigaiha’ were extremely narrow compared with the wild type. In contrast to the normal pistil of the wild type, ‘Hanaguruma’ and ‘Gin-no-zai’, normal and malformed pistils we’re observed in ‘Seigaiha’. Epidermal cell size was not related to the narrowness of lateral organs in the wild-type and sai-zaki cultivars. These results indicate that the sai-zaki trait of materials, at least ‘Seigaiha’, would be a common mutation in the growth of lateral organs in the transverse plane. All sai-zaki cultivars showed fertility. The sai-zaki trait of old Japanese cultivars from the Edo era is expected to provide new breeding material that offers the opportunity to generate additional morphological novelties.