The greenalgae (singular: green alga) are a large, informal grouping of algae consisting of the Chlorophyte and Charophyte/Streptophyta, which are now placed in separate divisions, as well as the more basal Mesostigmatophyceae and Chlorokybophyceae.
The land plants, or embryophytes, are thought to have emerged from the charophytes. Therefore, cladistically, embryophytes belong to greenalgae as well. However, because the embryophytes are traditionally classified as neither algae nor greenalgae, greenalgae are a paraphyletic group. Since the realization that the embryophytes emerged from within the greenalgae, some authors are starting to include them. The clade that includes both greenalgae and embryophytes is monophyletic and is referred to as the clade Viridiplantae and as the kingdom Plantae. The greenalgae include unicellular and colonial flagellates, most with two flagella per cell, as well as various colonial, coccoid and filamentous forms, and macroscopic, multicellular seaweeds. There are about 8,000 species of greenalgae. Many species live most of their lives as single cells, while other species form coenobia (colonies), long filaments, or highly differentiated macroscopic seaweeds.
A few other organisms rely on greenalgae to conduct photosynthesis for them.
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