METABOLIC ADAPTATIONS. “Seven PSGs were related to the photosynthetic pathway and may reflect adaptations to new conditions of carbon fixation and photosynthesis that seagrasses had to face after their split from a terrestrial ancestor. Fixation of CO2 is expected to be more difficult for seagrasses since seawater contains very little dissolved carbon dioxide.” (PSGs= positively selected genes).
http://bmcevolbiol.biomedcentral.com/articles/10.1186/1471-2148-11-8