Hanson, M. R., and Sattarzadeh, A. (2008) Dynamic morphology of plastids and stromules in angiosperm plants, Plant, cell & environment 31, 646 - 657. (hansonlab.org)
In early angiosperms, a different and much faster mechanism evolved. (discovermagazine.com)
When Charles Darwin looked at the fossil record, he was amazed at how many different kinds of angiosperms evolved so quickly, calling this burst «an abominable mystery.» (sciencemag.org)