We may finally understand why tropical plants have huge leaves

Why do plants’ leaves shrink the further from the equator they grow? It may all be to do with maintaining a comfortable temperature.

Leaves vary greatly in size, from less than 1 square millimetre to almost 1 square metre. Large-leaved plants like bananas and palms tend to live in the tropics, while small-leaved plants like heather and clover are found closer to the poles.

Botanists first noticed this latitude trend in the 19th century, but nobody has convincingly explained it. One idea is that leaf size is important for preventing overheating. But large leaves absorb more of the sun’s heat and get hotter than small ones, suggesting they should be found in cold regions, not the tropics.

To solve this puzzle, Ian Wright at Macquarie University in Sydney and his colleagues studied the leaves of 7670 plant species found at different latitudes. The team looked at the relationship between leaf size and various aspects of climate, including day and night temperatures, rainfall and humidity.

They found that avoiding night-time freezing is just as important for plants as avoiding daytime heat stress.=READ MORE