Morphological differentiations between subspecies in Arisaema thunbergii (Araceae) with special reference to sexual dimorphism

In Arisaema thunbergii Blume, two Japanese subspecies, subsp. thunbergii and subsp. urashima (H. Hara) H. Ohashi & J. Murata, and subsp. autumnale J. C. Wang, J. Murata & H. Ohashi, recently described from Taiwan, have been recognized. Morphological variations in A. thunbergii between these subspecies are examined with special reference to sexual dimorphism and are discussed here in order to characterize each subspecies more clearly. We observed natural populations of subsp. autumnale in Taiwan and examined the number of leaflets and the length of peduncle, petiole, rachis, and terminal leaflet using dried specimens of all the subspecies. Differences between sexes were recognized in the peduncle/petiole length ratio in all subspecies. The degree of difference was most extreme in subsp. autumnale. The Taiwanese subsp. autumanale could be distinguished from the other subspecies in every character examined, while Japanese subspecies showed some similarities in leaf morphology and dissimilarities in peduncle length to each other. The differences in morphology and flowering season may suggest that the Taiwanese subspecies is a distinct species.