Plants that live in the ocean:
Kelp: kelp have holdfasts instead of roots.these hold onto rocks to keep the kelp fro, getting washed away. It also has gas bladders that keep the fronds afloat.
Red algae: algae varies its pigments so that it can take in more sunlight. It also reproduces sexually and asexually increasing its survival chances.
Sea grass:sea grass has horizontal roots that keep them in place when waves brush up. They are able to withstand many varieties of salinity. Also, they are able to withstand temperatures from 6 to 40 degrees Celsius. Or 48 to 104 degrees in Fahrenheit.
Phytoplankton: phytoplankton have an increased buoyancy