Plastid origins.

There has long been controversy over whether the plastids of green plants and algae, rhodophytes and chromophytes arose from a single primary endosymbiotic event or independently from several. DNA sequences from plastid genes are rapidly becoming available, but limitations of current phylogenetic inference techniques make it difficult to draw firm conclusions at present. However, it is clear that the endosymbiotic uptake of photosynthetic prokaryotes or eukaryotes has been far from unique.