Dh. Les et al., PHYLOGENETIC STUDIES IN ALISMATIDAE, II - EVOLUTION OF MARINE ANGIOSPERMS (SEAGRASSES) AND HYDROPHILY, Systematic botany, 22(3), 1997, pp. 443-463
Aquatic species represent fewer than two percent of all flowering plan
ts, and only 18 aquatic genera have acquired true hydrophily (water-po
llination) which is associated with an unusually high incidence of uni
sexual flowers. From the subset of submersed, hydrophilous angiosperms
, only 13 genera have colonized marine habitats. The evolution of hydr
ophily, unisexuality, and marine habit in angiosperms was explored usi
ng estimates of phylogeny obtained by phylogenetic analyses of chlorop
last (rbcL) gene sequence data. Despite what might appear to be diffic
ult evolutionary transitions, hydrophiles are highly polyphyletic with
independent origins in the monocotyledon subclass Alismatidae in addi
tion to two derivations in Be dicotyledon families Ceratophyllaceae an
d Callitrichaceae. Yet, even in alismatids, hydrophily has evolved man
y times. Unisexuality has also evolved repeatedly in the Alismatidae,
and is ancestral to the evolution of hydrophiles and marine plants in
the Hydrocharitaceae, Marine angiosperms (known only from Alismatidae)
have evolved in three separate lineages. The multiple origins of hydr
ophilous, marine plants offer an extraordinary example of convergent e
volution in angiosperms.