Some people include seagrasses, which are actually flowering plants that have managed to colonise the ocean, but only about 55 of them. There are about 10,000 species of seaweeds, very few compared to the 235,000 or so species of flowering plants. Most red and brown seaweeds are marine, but the vast majority of green-coloured algae are freshwater and terrestrial. All seaweeds, except for a few supposed parasites, are photosynthetic and oxygen-evolving. Seaweeds grow mostly on rocky areas or on coral reefs in what is a very narrow band between the highest reach of the tide and tidal waters to the deepest depths that light can penetrate.
Seaweeds are simple organisms that are hard to understand.
They are not quite plants and they are definitely not animals. Seaweeds are not yukky, horrible, slimy things to everybody. On this site you will find much information on seaweeds and their uses .