Seasonal growth and reproductive ecology of two threatened aquatic macrophytes, Blyxa aubertii and B-echinosperma (Hydrocharitaceae), in irrigation ponds of south-western Japan

Ecological life history and reproductive traits of two threatened aquatic m acrophytes, Blyxa aubertii L.C. Richard and B, echinosperma (Clarke) Hooker , were studied in irrigation ponds in southwestern Japan. The size of plant s varied greatly in both species but reproductive allocation was nearly con stant irrespective of plant size at reproductive stage, amounting to 31.8% and 45.9% at maximum in B, aubertii and B. echinosperma, respectively. The number of flowers and total number of seeds produced per individual were as sociated significantly with plant size. Seeds were produced by self-pollina tion both in emerged and submerged cleistogamous flowers and seed set rate of the two species was very high. These traits are considered to be adaptiv e to unstable environments that are liable to water level fluctuations, suc h as rice-fields and irrigation ponds.