The glaucophytes, also referred to as glaucocystophytes or glaucocystids, 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.
It is thought that the green algae (from which the higher plants evolved), red algae and glaucophytes acquired their chloroplasts from endosymbiotic cyanobacteria. The other types of algae received their chloroplasts through secondary endosymbiosis, by engulfing one of those types of algae along with their chloroplasts.
The glaucophytes are of obvious interest to biologists studying the development of chloroplasts: 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 all of these developed.
The chloroplasts of glaucophytes, like the cyanobacteria and the chloroplasts of red algae, use phycobiliproteins to capture some wavelengths of light; the green algae and higher plants have lost that pigment.
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.
The three main genera included are:
- 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.