Algae on wood

Algae is a very large and diverse group of eukaryotic organisms, ranging from unicellular genera such as Chlorella and the diatoms to multicellular forms such as the giant kelp, a large brown alga that may grow up to 50 meters in length. Most are autotrophic and lack many of the distinct cell and tissue types found in land plants such as stomata, xylem and phloem.