Abstract
The floral biology of Ludwigia ovalis Miq. (Onagraceae) was investigated in the field and under cultivation. It was confirmed that cleistogamous flowers were formed on submerged shoots and successfully set seed by self-pollination. Chasmogamous flowers on emergent and terrestrial shoots opened early in the morning and anthesis occurred on the same day. The stamens leaned toward the stigma in late afternoon, resulting in autonomous self-pollination. High fruit and seed sets of bagged flowers supported the dominance of autogamy. In addition, six ant species were observed to visit the flowers and forage for nectar. They moved around on the flowers and promoted geitonogamy and/or cross pollination as well as selfpollination. Although pollination by ants has often been negatively discussed, the present study showed that ants can play the role of pollinators in L. ovalis.
