Macroalgal seaweeds primarily occur in two kingdoms, the Plantae and Chromista. The phylum Charophyta, in the kingdom Plantae, has about 4400 species that are primarily freshwater taxa. The class Charophyceae within the Charophyta contains about 700 species with only a few species occurring in estuarine habitats. Of the 6000 species in the phylum Chlorophyta in the kingdom Plantae, about 10% are marine and mostly placed in the class Ulvophyceae (c. 700 species) and order Ulvales. The brown algae are in the kingdom Chromista, phylum Ochrophyta, and class Phaeophyceae and have about 2040 species of which all but 10 genera occur in marine habitats. Large brown macroalgae or seaweeds can be found in about half of the 21 orders, but they are most common in the Desmarestiales, Dictyotales, Ectocarpales, Fucales, and Laminariales. The phylum Rhodophyta, also in the kingdom Plantae, has about 7100 species that are placed in three subphyla of which the Eurhodophytina is the largest with about 6900 species. Only about 3% of the taxa (c. 150 species) occur in freshwater habitats. The subphyla contain two classes, the Bangiophyceae (198 species) and Florideophyceae (c. 6700 species), which has most of the larger red macroalgae.