ABSTRACT
The initiation of flowering in R. penicillatus var. calcareus is probably not controlled by a photoperiodic effect. Experiments carried out in growth chambers showed that the plants flowered under a light period of 8 hr, 15 hr, and 12 hr. The petals of R. penicillatus var. calcareus are white, those of R. sceleratus yellow. R. sceleratus appeared to be a LDP as flowering was observed under an 18-hr photoperiod but not under an 8-hr photoperiod. Floral initiation and stem growth in R. sceleratus is similar to that found in many rosette LD plants. Once flowers have been initiated, growth continues slowly with the development of numerous laterally inserted flowers. However, there is a special adaptation to the aquatic habitat which implies that the flower stalk can respond to submergence.
