A brief history of plastids and their hosts.

Plastids are photosynthetic organelles and their nonphotosynthetic derivatives found in plants and algae. They have many names, depending on their colour or function, including chloroplasts, chromoplasts, leucoplasts, or apicoplasts, but all of these are homologous structures tracing back to a single origin. Plastids are most commonly associated with photosynthesis, but are generally metabolically diverse organelles, having been found to function in controlling oxidative stress as well as the biosynthesis of fatty acids, isoprenoids, heme, amino acids, and other small compounds. The great diversity of plastids, and the organisms that harbour them, have made plastid evolution one of the more interesting challenges in reconstructing eukaryotic macroevolutionary history – a challenge that has been made even more intriguing by the unexpected twists and turns that plastid evolution is now known to have taken. Despite its complexity, the events surrounding the origin and spread of plastids are now unfolding to reveal a complex history with unexpected impacts on eukaryotic evolution and biodiversity (Fig. 1).