PHYLOGENY OF THE FAMILY HYDROCHARITACEAE INFERRED FROM RBCL AND MATK GENE SEQUENCE DATA

The family Hydrocharitaceae, with 15 genera and ca. 80 species, shows a remarkable morphological diversity which presumably developed as an adaptation to their aquatic habitat. This is particularly true in the case of the many different kinds of pollination mechanisms. To gather more basic information regarding the adaptive evolution of Hydrocharit aceae, we have carried out a phylogenetic analysis based on the sequen ces of the rbcL and matK. Our resulting neighbor-joining distance tree provides the following insights: (1) none of the previous classificat ion systems were supported by molecular phylogenetic tree; (2) Najas ( Najadaceae), which has never been included in Hydrocharitaceae except in Shaffer-Fehre's (1991) system based on seed coat structures, is an ingroup of Hydrocharitaceae; (3) Limnocharitaceae and Alismataceae are sister groups of Hydrocharitaceae; (4) the three marine genera, Halop hila, Enhalus and Thalassia, are monophyletic; and (5) a peculiar poll ination mechanism specific to Hydrocharitaceae (Hydrocharitaceae-epihy drophily), underwent a parallel evolution.