Original: Algae ( or ; singular alga , Latin for '' seaweed '' ) are a large and diverse group of simple , typically autotrophic organisms , ranging from unicellular to multicellular forms , such as the giant kelps that grow to 65 meters in length .
Simplified: Though the prokaryotic Cyanobacteria ( formerly referred to as blue-green algae ) were included as '' Algae '' in older textbooks , this is outdated .