Cymodoceaceae is one of four families to have developed filamentous
pollen, along with Ruppiaceae, Zosteraceae, and Posidonaceae. The pollen is assembled as long and thin grains rather than spheres, which increases its surface area when floating on the water. In addition, the pollen can more easily form pollen rafts, enabling distribution over a large surface area of water. The pollen is
epihydrophilous (pollen distributed on the surface of the water) or hypohydrophilous (pollen distributed below the surface of the water) depending on the genera. There are three different methods used. Species in
Halodule and
Cymodocea release pollen at low tide, where it floats and assembles into snowflake-like pollen rafts which then hopefully make contact with the stigmas when the tide starts coming back in.
Amphibolis and
Thalassodendron have pollen that is carried up to and then released upon the surface of the water by
abscisent male flowers.
Syringodium has pollen grains that are approximately the same density as seawater and form small clumps which move beneath the surface by submarine currents to the stigmas of female flowers. There are two leading theories regarding the prevalence of dioecy in Cymodoceaceae. The construction and reception of pollen rafts are bulky operations. To have either perfect flowers or bear both male and female flowers on one plant could interfere with successful fertilization. The other theory is it would ensure cross-pollination in an environment that would make self-pollination much more likely, a process that would limit the gene pool and make plants more susceptible to variable conditions or disease. Two genera have
viviparous seedlings. The seeds of
Amphibolis and
Thalassodendron lack seed coats and do not store starch or other important nutrients. They instead latch onto the parent plant immediately after germination. The seedling develops a footing tissue from the hypocotyl, which attaches to the parents through transfer cells. The seedlings develop leafy shoots over the course of 7–12 months before being released.
Amphibolis seedlings develop a grappling apparatus which serves to anchor the seedling to a substrate once released whereas the seedlings of
Thalassodendron are released from an enveloping bract. As the external wall of the footing tissue in the seeds is apoplastic, the seedlings can be considered parasitic on and also cytoplasmically isolated from the maternal tissue. ==References==