The anatomical and morphological evidence indicates that seagrasses evolved from fresh water ancestors (Arber, 1920).
Adaptations for life in submerged saline environments
Surf grasses along other seagrasses have the ability to grow completely submerged underwater at all times. Surf grasses have no stomata and do osmoregulation primarily in epidermal cells. Due to the surf grasses extremely thin cuticle, desiccation and bleacing occur rapidly at low tide when plants are exposed to wind and elevated temperatures. The epidermis is the main site of photosynthesis within the leaves. Since surf grass is always submerged it has evolved reduced water conducting systems and anchoring systems that help it withstand wave action. Surf grasses have the ability to perform hydrophilic pollination on the surface of water and in submerged environments.
(Den Hartog, 1970; Larkum, 2006)
Arber A (1920) Water Plants. Cambridge University Press.
Reprinted 1972 by Verlag Von J. Cramer, Lehre.
Den Hartog C (1970) Seagrasses of the world. North Holland Publ., The Netherlands.
Larkum, Anthony W.D., Orth, Robert J., Duarte, Carlos M. Seagrasses: Biology, Ecology and Conservation. Springer 2006. p.92
Larkum, Anthony W.D., Orth, Robert J., Duarte, Carlos M. Seagrasses: Biology, Ecology and Conservation. Springer 2006.