STUDIES OF HYBRIDIZATION AND CHROMOSOME-NUMBER VARIATION IN AQUATIC ANGIOSPERMS - EVOLUTIONARY IMPLICATIONS

Aquatic angiosperms are widely recognized as a biological group sharing attributes associated with adaptations to the aquatic condition. Clonal growth, high vagility of vegetative propagules, and rare to sporadic sexual reproduction are common convergences among aquatic plants, and play central, interacting roles in various evolutionary factors. In this review, two important evolutionary factors, hybridization and chromosome number variation, are discussed with respect to interactions involving clonal growth, vagility, and asexuality. Asexual reproduction emerges as a significant evolutionary catalyst allowing for the perpetuation of hybrid offspring and anomalous cytotypic variants. Inherent phenotypic plasticity in aquatic plants is difficult to discern from both hybrid individuals and cytotypic variants. Detailed studies of putative 'hybrids' in some groups may reveal a higher incidence of cytotypic variants at the basis of morphological differences previously attributed to hybridization.