Before flowering plants (angiosperms) appeared on earth, conifers (gymnosperms) ruled the roost in the plant world. But the rapid radiation of angiosperms pushed most conifers into marginal habitats around 65 million years ago.
However a recent study (Biffin et al 2011), using molecular methods to determine the genetic relationship amongst species, investigated the idea that evolving a more flattened leaf shape, rather than a typical pine needle, allowed some conifers in the southern hemiphere, known as podocarps, or plum pines, to co-exist with flowering plants. A more flattened leaf shape allows the podocarps to capture more light under the canopy formed by leafy angiosperms.
The study pinpoints the changing shape of the podocarp leaf shape as beginning around 60 million years ago. Competition between podocarps and angiosperms resulted in flattened leaves evolving several times among conifers, and drastically affecting the geographic range of podocarps – today their highest diversity is found in tropical rainforests.
‘Pine evolved to resist rise of flower power’ ABC Science (website), Wednesday, 8 June 2011 by Rachel Sullivan (relating to Biffin et al 2011, publication): http://www.abc.net.au/science/articles/2011/06/08/3238500.htm
For more information see: Biffin et al. (2012) Leaf evolution in Southern Hemisphere conifers tracks the angiosperm ecological radiation. Proceedings of the Royal Society, Biological Science. doi: 10.1098/rspb.2011.0559