Alga

Algae Fossil range: Mesoproterozoic–present Had'n Archean Proterozoic Pha.
A variety of algae growing on the sea bed in shallow waters
Scientific classification
Domain: Eukaryota, Bacteria
Included groups
Archaeplastida Plantae Chlorophyta (green algae) Charophyta (green algae) Rhodophyta (red algae) Glaucophyta Rhizaria, Excavata Chlorarachniophytes Euglenids Chromista, Alveolata Heterokonts Bacillariophyceae (Diatoms) Axodines Bolidomonas Eustigmatophyceae Phaeophyceae (brown algae) Chrysophyceae (golden algae) Raphidophyceae Synurophyceae Xanthophyceae (yellow-green algae) Cryptophyta Dinoflagellata Haptophyta Cyanobacteria (blue-green algae)
Excluded groups
Bacteria (non-photosynthetic) Protista (non-photosynthetic) Animalia Embryophyta Fungi

Algae (/ˈældʒi, ˈælɡi/; singular alga /ˈælɡə/) is an informal term for a large, diverse group of photosynthetic organisms which are not necessarily closely related, and is thus polyphyletic. Included organisms range from unicellular genera, such as Chlorella and the diatoms, to multicellular forms, such as the giant kelp, a large brown alga which may grow up to 50 m in length. Most are aquatic and autotrophic and lack many of the distinct cell and tissue types, such as stomata, xylem, and phloem, which are found in land plants. The largest and most complex marine algae are called seaweeds, while the most complex freshwater forms are the Charophyta, a division of green algae which includes, for example, Spirogyra and the stoneworts.