Algae
![The lineage of algae according to Thomas Cavalier-Smith. The exact number and placement of endosymbiotic events is currently unknown, so this diagram can be taken only as a general guide.[2][3] It represents the most parsimonious way of explaining the three types of endosymbiotic origins of plastids. These types include the endosymbiotic events of cyanobacteria, red algae and green algae, leading to the hypothesis of the supergroups Archaeplastida, Chromalveolata and Cabozoa respectively. Endosymbiotic events are noted by dotted lines.](/uploads/202502/02/AlgaeTree2242.png)
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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 are 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 meters 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.