Chlorophyta is a division of green algae informally called chlorophytes.

Chlorophytes are eukaryotic organisms composed of cells with a variety of coverings or walls, and usually a single green chloroplast in each cell. They are structurally diverse: most groups of chlorophytes are unicellular, such as the earliest-diverging prasinophytes, but in two major classes (Chlorophyceae and Ulvophyceae) there is an evolutionary trend toward various types of complex colonies and even multicellularity.

Chlorophyte cells contain green chloroplasts surrounded by a double-membrane envelope. These contain chlorophylls a and b, and the carotenoids carotin, lutein, zeaxanthin, antheraxanthin, violaxanthin, and neoxanthin, which are also present in the leaves of land plants. Some special carotenoids are present in certain groups, or are synthesized under specific environmental factors, such as siphonaxanthin, prasinoxanthin, echinenone, canthaxanthin, loroxanthin, and astaxanthin. They accumulate carotenoids under nitrogen deficiency, high irradiance of sunlight, or high salinity. In addition, they store starch inside the chloroplast as carbohydrate reserves. The thylakoids can appear single or in stacks. In contrast to other divisions of algae such as Ochrophyta, chlorophytes lack a chloroplast endoplasmic reticulum.

Chlorophytes often form flagellate cells that generally have two or four flagella of equal length, although in prasinophytes heteromorphic (i.e. differently shaped) flagella are common because different stages of flagellar maturation are displayed in the same cell. Flagella have been independently lost in some groups, such as the Chlorococcales. Flagellate chlorophyte cells have symmetrical cross-shaped ('cruciate') root systems, in which ciliary rootlets with a variable high number of microtubules alternate with rootlets composed of just two microtubules; this forms an arrangement known as the "X-2-X-2" arrangement, unique to chlorophytes. They are also distinguished from streptophytes by the place where their flagella are inserted: directly at the cell apex, whereas streptophyte flagella are inserted at the sides of the cell apex (sub-apically).

Below the flagellar apparatus of prasinophytes are rhizoplasts, contractile muscle-like structures that sometimes connect with the chloroplast or the cell membrane. In core chlorophytes, this structure connects directly with the surface of the nucleus.

The surface of flagella lacks microtubular hairs, but some genera present scales or fibrillar hairs. The earliest-branching groups have flagella often covered in at least one layer of scales, if not naked.

Chlorophytes and streptophytes differ in the enzymes and organelles involved in photorespiration. Chlorophyte algae use a dehydrogenase inside the mitochondria to process glycolate during photorespiration. In contrast, streptophytes (including land plants) use peroxisomes that contain glycolate oxidase, which converts glycolate to glycoxylate, and the hydrogen peroxide created as a subproduct is reduced by catalases located in the same organelles.

Asexual reproduction is widely observed in chlorophytes. Among core chlorophytes, both unicellular groups can reproduce asexually through autospores, wall-less zoospores, fragmentation, plain cell division, and exceptionally budding. Multicellular thalli can reproduce asexually through motile zoospores, non-motile aplanospores, autospores, filament fragmentation, differentiated resting cells, and even unmated gametes. Colonial groups can reproduce asexually through the formation of autocolonies, where each cell divides to form a colony with the same number and arrangement of cells as the parent colony.