algae

Most of the plants that live on the intertidal rocky shore, or under the water along our seashores, are algae. Most people call these algae plants seaweed, or kelp.
There are a few underwater-living flowering plants, called seagrasses. They usually live in saltwater estuaries. Some also live along our ocean shores. Like land plants, these flowering plants have a root system to take up nutrients. They absorb sunlight through their leaves and have small flowers for reproduction. Algae are quite different.
Algae
Algae have quite a number of features which make them unlike normal land-based flowering plants.
Firstly, they do not have a root system which takes up nutrients. Algae take their food in through their leaf-like fronds which are surrounded by nutrient-carrying seawater. Their "roots" are are called holdfasts, and that is what they do. They hold the algae down firmly onto the rock surface.
Algae also reproduce quite differently to the flowering plants. They have spores like the ferns, mosses, lichens and liverworts.
Algae are divided into three main groups. There are green, brown and red algae, which differ in having different photosynthetic pigment systems.
Green Algae - Phylum Chlorophyta
Green algae get their colour from the photosynthetic chlorophyll pigments. They come in a variety of shapes including flat sheets, cylinders, strings of beads, spheres, or hair-like filaments.
Green algae are common in the intertidal zones and in shallow water as well as in some freshwater habitats, where light is plentiful.
Some examples of Green Algae are: