ENORMOUS EVOLUTIONARY GAP. “This Botanical Briefing reviews how the integration of palaeontology, geochemistry and developmental biology is providing a new mechanistic framework for interpreting the 40- to 50-million-year gap between the origination of vascular land plants and the advent of large (megaphyll) leaves, a long-standing puzzle in evolutionary biology.”
http://aob.oxfordjournals.org/content/96/3/345.full.pdf