Plants which grow in salt water is known as

Plants that grow in salt water are known as Halophytes.
A halophyte is a salt-tolerant plant that grows in soil or waters of high salinity, coming into contact with saline water through its roots or by salt sprays, such as in saline semi-deserts, mangrove swamps, marshes and sloughs and seashores.
Plants that avoid the effects of high salt even though they live in a saline environment may be referred to as facultative halophytes rather than 'true', or obligatory, halophytes.