UCLA life scientists have discovered new laws that determine the construction of leaf vein systems as leaves grow and evolve. These easy-to-apply mathematical rules can now be used to better predict the climates of the past using the fossil record.

The research, published May 15 in the journal Nature Communications, has a range of fundamental implications for global ecology and allows researchers to estimate original leaf sizes from just a fragment of a leaf. This will improve scientists' prediction and interpretation of climate in the deep past from leaf fossils.

Leaf veins are of tremendous importance in a plant's life, providing the nutrients and water that leaves need to conduct photosynthesis and supporting them in capturing sunlight. Leaf size is also of great importance for plants' adaptation to their environment, with smaller leaves being found in drier, sunnier places.

However, little has been known about what determines the architecture of leaf veins. Mathematical linkages between leaf vein systems and leaf size have the potential to explain important natural patterns. The new UCLA research focused on these linkages for plant species distributed around the globe.

"We found extremely strong, developmentally based scaling of leaf size and venation that has remained unnoticed until now," said Lawren Sack, a UCLA professor of ecology and evolutionary biology and lead author of the research.

How does the structure of leaf vein systems depend on leaf size? Sack and members of his laboratory observed striking patterns in several studies of just a few species. Leaf vein systems are made up of major veins (the first three branching "orders," which are large and visible to the naked eye) and minor veins, (the mesh embedded within the leaf, which makes up most of the vein length).

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