The glaucophytes, also known as glaucocystophytes or glaucocystids, are a small group of unicellular algae found in freshwater and moist terrestrial environments, less common today than they were during the Proterozoic. The stated number of species in the group varies from about 14 to 26. Together with the much larger sister taxa Rhodophyta (red algae) and Viridiplantae/Chloroplastida (green algae and land plants), they form the primary algae clade Archaeplastida. The glaucophytes are of interest to biologists studying the evolution of chloroplasts as they may be similar to the ancestral algal type that led to the red algae and green plants, i.e. glaucophytes may be basal archaeplastids.
Reproduction Unlike red and green algae, glaucophytes reproduce exclusively through asexual means.. They undergo open mitosis without centrioles, a trait shared with other basal eukaryotes. Reproductive modes include binary fission, zoospore formation, and autosporulation. For example, Cyanophora paradoxa divides longitudinally, producing two daughter cells, each inheriting a single cyanelle. Species of Glaucocystis reproduce via non-motile autospores. To date, there is no evidence of sexual reproduction in glaucophytes.
Characteristics The plastids of glaucophytes are known as 'muroplasts', 'cyanoplasts', or 'cyanelles'. Unlike the plastids in other organisms, they have a peptidoglycan layer, believed to be a relic of the endosymbiotic origin of plastids from cyanobacteria. This peptidoglycan layer plays a functional role in plastid division and is considered molecular evidence of their cyanobacterial ancestry. Glaucophytes contain the photosynthetic pigment chlorophyll a. Along with red algae and cyanobacteria, they harvest light via phycobilisomes, structures consisting largely of phycobiliproteins. The green algae and land plants have lost that pigment. Like red algae, and in contrast to green algae and plants, glaucophytes store fixed carbon in the cytosol. This cytosolic carbon fixation, rather than fixation within plastids, is considered a retained ancestral trait. Glaucophyte phycobilisomes are composed primarily of phycocyanin and allophycocyanin, two key pigments also present in cyanobacteria. These pigments allow absorption of light at wavelengths that chlorophyll cannot, enhancing light harvesting in low-light aquatic environments. Studies of endosymbiotic gene transfer (EGT) suggest that several genes originally encoded in cyanobacterial ancestors have been relocated to the nuclear genome in glaucophytes, reflecting early stages of plastid-host genomic integration. The evolution of glycogen and starch metabolism in eukaryotes gives molecular clues to understand the establishment of plastid endosymbiosis. The most early-diverging genus is Cyanophora, which only has one or two plastids. When there are two, they are semi-connected. 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.
Phylogeny
External Together with red algae and Viridiplantae (green algae and land plants), glaucophytes form the Archaeplastida – a group of plastid-containing organisms that may share a unique common ancestor that established an endosymbiotic association with a cyanobacterium. The relationship among the three groups remains uncertain, although it is most likely that glaucophytes diverged first:
The alternative, that glaucophytes and red algae form a clade, has been shown to be less plausible, but cannot be ruled out.
Internal The internal phylogeny of the glaucophytes and the number of genera and species varies considerably among taxonomic sources. A phylogeny of the Glaucophyta published in 2017 divided the group into three families, and includes five genera:
Taxonomy
A 2019 list of the described glaucophyte species has the same three subdivisions, treated as orders, but includes a further five unplaced possible species, producing a total of between 14 and 19 possible species.
Order Cyanophorales Genus Cyanophora – 5–6 species Order Glaucocystales Genus Glaucocystis – 7–8 species Order Gloeochaetales Cyanoptyche – 1 species Gloeochaete – 1 species Other possible species ?Archaeopsis monococca Skuja ?Chalarodora azurea Pascher ?Glaucocystopsis africana Bourrelly ?Peliaina cyanea Pascher ?Strobilomonas cyaneus Schiller As of May 2026, AlgaeBase divided glaucophytes into only two groups, placing Cyanophora in Glaucocystales rather than Cyanophorales (however the entry was dated 2011). AlgaeBase included a total of 25 species in eight genera:
Glaucocystales Chalarodora Pascher – 1 species Cyanophora Korshikov – 6 species Glaucocystis Itzigsohn – 13 species Glaucocystopsis Bourrelly – 1 species Peliaina Pascher – 1 species Strobilomonas Schiller – 1 species Gloeochaetales Cyanoptyche Pascher – 1 species Gloeochaete Lagerheim – 1 species None of the species of Glaucophyta is particularly common in nature. The glaucophytes were considered before as part of family Oocystaceae, in the order Chlorococcales.
References
