Abstract
Aquatic and semi-aquatic plants often display heterophylly. Since the leaf form is easily altered by submergence, examination with heterophyllous plants would provide clues to understand the determination of leaf shape. When terrestrially grown Ludwigia arcuata (Onagraceae) were transferred to under submergence, newly developed leaves showed typical submerged-type shape, while some preexisted primordia were developed into leaves with amphibious shapes between terrestrial and submerged-type, in which only basal portions could respond to submergence. This indicated that the developmental fate of distal portions had been already fixed as terrestrial-type tissues, while that of basal portions had not been determined before submergence. Thus, the fate of basal portions was determined after submergence. Considering that shapes of primordia of terrestrial and submerged leaves were morphologically almost identical in their early developmental stages, the leaf form would be determined basipetally and temporally upon heterophyllous plants.
