Allozyme variations and classification of Trapa (Trapaceae) in Japan

Trapa L. (Trapaceae) is one of the most common aquatic plants in Japan. However, its taxonomic treatment has differed among authors. As a step toward a revision of Japanese Trapa, we analyzed allozymes in plant samples collected from 55 populations and tentatively classified into 6 taxa. Allozyme analysis indicated three distinct groups corresponding to the size class of the fruits: T. incisa (small), T. japonica group (medium), and T. natans group (large). The development of lower protuberances or spines and the presence or absence of tubercles had no correspondence to allozymic differentiation and thus are to be considered as variants within taxa. Fixed heterozygosity found in the T. japonica group indicates that the group might be of hybrid origin between T. incisa and plants of the T. natans group.