Chlorophyta

Chlorophyta is a division of green algae comprising a diverse group of photosynthetic eukaryotes that carry chlorophyll a and chlorophyll b and lack the red algal phycobiliproteins. They store energy as starch and have cellulose-based cell walls. Chlorophyte plastids typically possess well-developed internal thylakoid membranes and, in many species, a pyrenoid. They inhabit a wide range of aquatic and moist terrestrial environments and include both microscopic and macroscopic forms.

Body plans range from unicellular flagellates such as Chlamydomonas to colonial forms like Volvox, and from filamentous strands such as Spirogyra to laminated or sheet-like thalli in Ulva. The group includes terrestrial green algae, as well as marine and freshwater species, many of which contribute to biofilms and phytoplankton communities.

Reproduction is diverse. Asexual reproduction occurs by mitotic divisions, fragmentation, or flagellated spores. Sexual reproduction can be isogamous, anisogamous, or oogamous, and life cycles may be haplontic, diplontic, or show alternation of generations, depending on the lineage. Some taxa, especially in Ulvophyceae, display complex alternations of generations.

Ecology and significance: Chlorophyta are important primary producers in aquatic ecosystems, forming substantial components of phytoplankton in freshwater and marine habitats. They contribute to global carbon fixation and serve as food for a wide range of invertebrates. Several species are model organisms in research, notably Chlamydomonas reinhardtii, used to study photosynthesis, flagellar function, and gene regulation.

Systematics: Chlorophyta includes several major lineages, commonly grouped as Chlorophyceae, Ulvophyceae, Trebouxiophyceae, and others. They are part of the larger supergroup Archaeplastida (Viridiplantae) and are considered the sister group of the Streptophyta, which contains the land plants. The division is subject to revision as molecular data refine green-algal phylogeny.