A further series of innovations in vascular plants, including the
biosynthesis of lignin and the origin of lateral meristems (cambium),
were critical to the development of large plants, and these
developments may have been stimulated by competition for light.
Trees evolved independently in several major groups, resulting in
stratified forest communities by the end of the Middle Devonian
and the production of large amounts of highly decay-resistant
organic material (in the form of lignified wood). The early evolution
of lignin-decomposing fungi (some Ascomycetes, and Basidiomycetes)
is still poorly understood24, but these groups would have
been essential for recycling much of the organic carbon.