Figure 1. Schematic flowchart representing the evolution of complex plastid.

A single endosymbiosis event gave raise to the primary plastids found in red and green algae and in glaucophytes. At least three separate events of secondary endosymbiosis gave raise to the complex plastids found in clorarachniophytes, euglenoids (green path) and in members of the chromalveolate superphylum (red path). Representative organisms for each of the resulting lineages are depicted as schemes and their corresponding cellular morphology is outlined. P; plastid, Number; number of plastid membranes, N; nucleaus, Nm; nucleomorph, G: Golgi apparatus, ER; endoplasmic reticulum. White arrows mark the pathway taken by nuclear/nucleomorph encoded proteins to the complex plastid in each organism. * Note that in dinoflagellates there is evidence for several independent secondary and tertiary endosymbioses that are not shown here. These involved green algal, haptophye, diatom and cryptomonad symbionts. See [88] for further reference to this fascinating complexity.