Which three groups contain large algae known as seaweeds? which three groups contain large algae known as seaweeds?

The three groups are green algae, red algae and brown algae. Seaweeds are a group of photoautotrophic, multicellular algae occurring in marine environments. They are simple organisms that can perform photosynthesis. They have characteristics such as they are non-vascular plants, flowerless, seedless, lack embryos and cells contain chlorophyll among other characteristics.