Archaeplastida

The Archaeplastida (or kingdom Plantae sensu lato "in a broad sense") are a major group of eukaryotes. It include the photoautotrophic red algae (Rhodophyta), green algae, land plants and the minor group glaucophytes. It also includes the Rhodelphidia, an eukaryotrophic flagellate that is sister to the Rhodophyta, and probably picozoans. The Archaeplastida have chloroplasts that are surrounded by two membranes.  All other groups which have chloroplasts, besides the amoeboid genus Paulinella, have chloroplasts surrounded by three or four membranes.

The cells of the Archaeplastida do not have centrioles. They have mitochondria with flat cristae. They usually have a cell wall that contains cellulose. Food is stored as starch. However, these characteristics are also shared with other eukaryotes. The main evidence that the Archaeplastida form a monophyletic group comes from genetic studies. These studies show their plastids probably had a single origin. Not all scientists agree with these studies.  Photosynthetic organisms with plastids of different origin (such as brown algae) do not belong to the Archaeplastida.

The archaeplastidans fall into two main evolutionary lines. The red algae are colored with chlorophyll a and phycobiliproteins, like most cyanobacteria, and accumulate starch outside the chloroplasts. The green algae and land plants are colored with chlorophylls a and b, but do not have phycobiliproteins. Also, starch is built up inside the chloroplasts. These two groups are called Viridiplantae (Latin for "green plants") or Chloroplastida. The glaucophytes have cyanobacterial color.  They are unusual as they havea cell wall within their plastids (called cyanelles).

Archaeplastida should not be confused with the older and obsolete name Archiplastideae. This term refers to cyanobacteria and other groups of bacteria.Copeland, H. F. (1956). The Classification of Lower Organisms. Palo Alto: Pacific Books, p. 29, .

References

Category:Eukaryotes