Growth and Turion Formation of Ceratophyllum demersum in a Shallow Lake in Japan.

Growth of shoots and the in situ turion formation rate of Ceratophyllum demersum wereinvestigated in the shallow eutrophic Lake Sagata (37°49'N, 138'53E), Japan. Almost 90% of the young shoots in spring originated from turions. Active growth of main shoots was observed from June to the end of July, with a growth rate of 0.98 cm day-1main shoot-1;that of the total shoot (including lateral shoots) was 5.21 cm day-1. Auto-fragmentation was observed at the end of August, and shortened shoots floated on the water surface. Water temperature at the onset of growth was suggested to be one of the more important factors for growth. Shoots had turions at the apices from October. The in situ rates of turion formation from shoots ranged from about 20% to a high of 55% from main shoots, against about 10% from lateral shoots. C. demersum produced 35.7 turions per 1 g dry weight of plant material.Fragmentation of shoots and turion formation on them are important means of distributing this species to new habitats.