MASSIVE ENDOSYMBIOSIS. “Rather than constituting a single clade that can be traced back to a single last common ancestor, plants (i.e. eukaryotic photoautotrophs) have multiple evolutionary origins presumably as a consequence of primary endosymbiotic events, giving rise to lineages like the Chlorophyta, or as a result of secondary endosymbiotic events, giving rise to others like the euglenids and chromists.”
http://aob.oxfordjournals.org/content/85/4/411.full.pdf