Seashore plants include microscopic, one-celled organisms, many kinds of seaweeds and seagrasses, and even some species of trees. The types of plants that grow in a particular region are determined by climate and the kind of shoreline surface—rocky, sandy, or muddy. Some sandy or muddy shores do not support plants because the soil is frequently disturbed.

Plants that live in the lower (sublittoral) zone along the seashore are surrounded by water at all times. For this reason, most have not developed the special tissues and organs for conserving water that are needed by plants on land. The surrounding water also offers support to these plants, helping to hold them upright. As a result, their stems are soft and flexible, allowing them to move with the currents without breaking.

Plants that live in the intertidal (littoral) zone must be the hardiest, because they are exposed to...