Green algae
Green algae are photosynthetic unicellular and multicellular protists that are related to land plants. The thallus of the unicellular mermaid's wineglass, "Acetabularia", can grow to several inches (perhaps 0.1 to 0.2 m) in length. The fronds of the similarly unicellular, and invasive "Caulerpa taxifolia" can grow up to a foot (0.3 m) long.