1. Green algae (Chlorophyta): These are the most diverse group of algae, with over 10,000 species. They are characterized by their green color due to the presence of chlorophylls a and b, and they store food as starch. Green algae are closely related to land plants, and some scientists believe they were the ancestors of plants.

2. Brown algae (Phaeophyceae): This group contains large, multicellular seaweeds, such as kelp. They are distinguished by their brown or olive color due to the presence of the pigment fucoxanthin. Brown algae store food as laminarin, a type of carbohydrate.

3. Red algae (Rhodophyta): This group contains mostly multicellular seaweeds, although there are some single-celled species. They have a reddish color due to the pigment phycoerythrin, which allows them to photosynthesize in deeper water than other algae. Red algae store food as floridean starch.