Archaeplastida

Archaeplastida is a eukaryotic clade comprising land plants, green algae, red algae, and glaucophytes. Its members trace their primary plastids to an ancestral cyanobacterial endosymbiosis.

Primary endosymbiosis: An evolutionary process in which a eukaryotic cell incorporates a prokaryote that becomes an organelle. It explains how the ancestor of Archaeplastida acquired plastids from a cyanobacterium.
Chloroplast: A photosynthetic plastid containing chlorophyll and the molecular machinery for converting light energy into chemical energy. It is the best-known photosynthetic form of the plastid inherited across much of the clade.
Viridiplantae: The green lineage comprising green algae and land plants, characterized by chlorophylls a and b. This lineage contains the familiar green plants alongside diverse green algae.
Secondary endosymbiosis: An evolutionary process in which a eukaryote incorporates another eukaryote that already contains a plastid. Many algae outside Archaeplastida gained plastids through this later route rather than primary endosymbiosis.
Plastid: A family of organelles in plants and algae, including chloroplasts and several nonphotosynthetic forms. Primary plastids are the defining inherited organelles shared across the clade.
Plastid genome: The DNA genome retained within a plastid, encoding a subset of organelle proteins and RNAs. Its genes and bacterial affinities preserve evidence of plastid ancestry.
Rhodophyta: The red algae, a diverse lineage of mostly marine photosynthetic eukaryotes. Red algae are a major Archaeplastida branch with distinctive pigments and plastid features.
Stramenopiles: A diverse eukaryotic group that includes diatoms, brown algae, and oomycetes. Photosynthetic stramenopiles carry plastids derived through secondary endosymbiosis, not the ancestral Archaeplastida plastid.
Cyanobacteria: A phylum of bacteria that performs oxygen-producing photosynthesis using chlorophyll a. An ancient cyanobacterium became the plastid-bearing endosymbiont in Archaeplastida’s ancestry.
Plastid fission: The division of a plastid into daughter plastids, coordinated by bacterial-derived and host-derived machinery. Plastid replication lets ancestral organelles pass into descendant Archaeplastida cells.

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