How do plants live in salt water?

The salinity of wetlands has a huge influence in the presence of plant species and its diversity. For example, in freshwater marshes, which have just 0 to 2 ppt of salinity, there is more than 90 species of plants. In salt marshes, which has a salinity >20 ppt, there is less than 20 plant species able to live there. 

The oyster grass (Spartina alterniflora) is well adapted for salt marshes, being 63% of the vegetation. 

Picture: Digital Atlas of Flora

This species can tolerate low salinity, but is has less competition in salt water because of its three essential characteristics:

• Ability of concentrate salt in cells at higher concentrations than sea water, so it maintains a balanced osmoregularity.
• It can excrete excess salt
• It has air tubes that take oxygen from the leaves to the roots.