Credit: N. CATTLIN/FLPA

Proc. R. Soc. B doi:10.1098/rspb.2008.1762 (2009)

A host of grasses, including crops such as maize (corn) and sugarcane, grow well in hot, dry conditions because they have evolved a more efficient type of photosynthesis, the C4 pathway, which requires less water than the more widespread C3 pathway.

Some scientists believe that C4 photosynthesis evolved to cope with drought, but others argue it was originally an adaptation to exposed habitats.

Colin Osborne and Robert Freckleton at the University of Sheffield, UK, have now settled the debate by analysing the habitats of 117 genera of grasses, representing 15 independent C4 lineages. They provide strong evidence that C4 plants first arose in open, tree-less environments. Once the pathway had evolved, however, C4 plants would have been able to adapt faster to dry environments than C3 plants.