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  • Archaeoplastida (Plantae)
    • Glaucophyta (with primitive cyanelles)
    • Rhodophyta (red algae)
      • Floridiophytes
      • Bangiophytes
      • Cyanidiophytes
    • Chloroplastida (green algae and plants)
      • Chlorophytes (green algae)
      • Charophytes
        • Plants (streptophytes)
    • Trebouxiophytes
    • Ulvophytes (sea lettuce)
    • Prasinophytes (tiny marine microalgae)
    • Mesostigma

About this Superkingdom

This group consists primarily of plants, green algae, and red algae. In this group, but not other groups of eukaryotic phototrophs, the plastids probably originated by direct symbiosis of cyanobacteria; in other groups, additional membrane layers around the plastids suggests that these were secondary symbiosis, i.e. symbiosis with a eukaryotic algae rather than a cyanobacterium. The plastids in this group probably have a single common origin; this also is not true of other eukaryotic phototrophs.

Most have cell walls comprised of cellulose, store starch, and contain mitochondria with flat cristae, but lack centrioles.


Most chloroplastids are unicellular, filamentous, or colonial, but a few are multicellular: green plants and sea lettuce. Multicellularity in these two groups arose independently. Chlorophytes (green algae) are mostly aquatic and flagellated, and are often colonial, and include the stoneworts and green plants. The other multicellular chloroplastids are the ulvophytes (sea lettuce), common green seaweed. The best known Prasinophyte is Ostreococcus, an abundant “microalgae”. Ostreococcus is easily mistaken for Bacteria, being only ca. 1um in diameter, and contain only a single plastid, a single mitochondrion, and most often a single flagellum. Trebouxiophytes are generally terrestrial algae, often being the algal component of lichens. The most familiar member is Chlorella, which is sold as a health food supplement. Mesostigma (the scaly green flagellate) is a freshwater genus that was recently shown to be a deep branch within the Chloroplastids

Example species : Thalassia testinum (turtle grass)

turtle grass
from the Conservation Services web site, Government of Bermuda

Turtle grass is one of the few truly marine flowering plants (i.e. it is an angiosperm). Turtle grass is the most abundant sea grass in Florida, the Gulf of Mexico, and the West Indies. It forms dense mats in shallow water, typically from the a few feet below low tide level to 10 meters (depending primarily on water clarity and wave surge). It grows very quickly in appropriate conditions, up to an inch per week, and 4 years from seed to seed. They reproduce vegetatively through either the rhizomes, or sexually via submerged flowers. Turtle grasses are grazed directly by turtles, urchins, and a few fish, but support a complex ecosystem including a wide of fish, crustaceans, and molluscs (including the Queen conch) that graze the epiphytic film covering the surface of the leaves


Rhodophytes are generally multicellular, abundant and diverse marine algae found worldwide. Relationships amongst the red algae are in dispute. Bangiophytes and floridiophytes probably represent a single group. Porphyra is the edible seaweed (nori). Like the chloroplastids, the rhodophytes have an “alternation of generation” reproductive cycle. Cyanidiophytes are obscure unicellular inhabitants of acidic hot springs.

Example species : Chondrus crispus (Irish moss, Carrageen moss)

carrageen moss
from wikicommons :

This is a common, small (ca. 1”) branched red seaweed in the north Atlantic. It grows attached to rocks in the intertidal zone, and broken fragments commonly wash ashore with the tide. It is a major source of carrageen (which makes up the bulk of the algal mass), an important food additive. When boiled, Irish moss becomes gelatinous, and when chilled is served as a drink or mixer for “male enhancement”. Like other rhodophytes, the life cycle alternates between gametophyte (iridescent in the photo above) and sporophyte (spotted above) stages.


Glaucophytes are a small group of freshwater algae that are notable because their plastids are extremely primitive, retaining much more of their cyanobacterial genome and cell structure, including a peptidoglycan cell wall.