The glaucophytes are a tiny group of freshwater algae. They are distinguished mainly by the presence of cyanelles, primitive chloroplasts which closely resemble cyanobacteria and retain a thin peptidoglycan wall between their two membranes. These are of obvious interest to biologists studying the development of chloroplasts from endosymbiotic cyanobacteria. If the hypothesis that primary chloroplasts had a single origin is correct, glaucophytes are closely related to both green plants and red algae, and may be similar to the original alga type from which they developed.

Glaucophytes have mitochondria with flat cristae, and undergo open mitosis without centrioles. Motile forms have two unequal flagella, which may have fine hairs and are anchored by a multilayered system of microtubules, both of which are similar to forms found in some green algae. There are three main genera included here. Glaucocystis is non-motile, though it retains very short vestigial flagella, and has a cellulose wall. Cyanophora is motile and lacks a cell wall. Gloeochaete has both motile and non-motile stages, and has a cell wall that does not appear to be composed of cellulose.

The group is often, and perhaps more properly, referred to as the glaucocystophytes or glaucocystids.