Understanding the Complex and Extraordinary Leaf Designs in Plants

The intricate and unusual leaf design of a Japanese plant helps advance research on leaf patterns and plant growth models.
Fabienne Lang

Presumably, not many of us have stopped to wonder how plants grow their beautiful leafy patterns. We take it for granted that they merely appear, without much thought or care as to whether or not there is a specific design to each and every shrub. 

However, patterns appear all across the flora surrounding us, and scientists can prove now it through math

Indeed, scientists have created models that mirror a number of nature's most famous designs. And, we're not only talking about plants in this case. For example, the Fibonacci sequence can be seen in sunflower seed arrangements, nautilus shells, and pine cones alike. 

What has been concluded is that the growth hormone, auxin, is moving along with the proteins and is transported through the length of a plant, and helps create the patterns.

That all being said and done, a few leaf patterns still remain a mystery. 

1. Japanese shrub model

Understanding the Complex and Extraordinary Leaf Designs in Plants
An Orixa japonica shrub with the various divergence angles of the leaves visible. Source: Wikimedia Commons

The Orixa Japonica, a Japanese plant with unusual patterns did not fit in with equations that typically explain plant designs. So, a team of researchers from the University of Tokyo decided to take a closer look, and update the model. 

According to the authors, the new model shared in a new study in PLOS Computational Biology, not only creates a replica of the previously unknown pattern, but it also displays another design in an improved method than was previously known.

“In most plants, phyllotactic patterns have symmetry—spiral symmetry or radial symmetry,” says University of Tokyo plant physiologist Munetaka Sugiyama, senior author of the new study.

“But in this special plant, Orixa japonica, the phyllotactic pattern is not symmetric, which is very interesting. More than 10 years ago, an idea came to me that some changes in the inhibitory power of each leaf primordium may explain this peculiar pattern.”

After numerous tests, the authors were able to create patterns that were extremely close to the original plant's ones, but not perfectly. 

Leaf age as a clue

This led them to add a component to their equations: the age of the leaf.

Previous research took the view that leaves did not change patterns over time, however, as Sugiyama points out, this constant is “not natural from the viewpoint of biology.”

Understanding the Complex and Extraordinary Leaf Designs in Plants
Aloe polyphylla at the University of California Botanical Garden. Source: Wikimedia Commons

With this new factor, the team succeeded in mimicking the elaborate leaf arrangements of the O. japonica, all through computerized growth.

To add the cherry on top of the cake, these new and improved equations also recreated all other common foliage patterns and were able to predict the natural frequencies of them more accurately than other models.

Ciera Martinez, a computational biologist not involved in the study, said: "Now we just have to look closer at the molecular mechanisms in real plants to try and discover what the model predicts."

There's always more work to be done, and Sugiyama's team's research is certainly not yet finished. They are working to keep improving their model so that it will generate all known phyllotactic patterns. 

“We don’t think our study is practically useful for society,” Sugiyama says. “But we hope that it will contribute to our understanding of the symmetric beauty in nature."

It all started with a Japanese shrub that didn't fit into any equations. 

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