A note about Heterophylly in the real world
Dan Russell
Friday, March 21, 2025
A note about Heterophylly in the real world
Our Challenge about leaf variation on an individual plant made me more observant in the real world...
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| Holly leaf variation on the same plant. Taken in Zürich by Dan. The left image is from 3 meters above the ground in an unpruned part of the plant. The right image, from a well-pruned part of the bush, is about 1 meter off the ground. |
... I hope that being a Regular Reader of SRS does the same for you as well.
I was out walking last week, not long after having written about Mimcry in Plants (March 14, 2025), when I happened to cross paths with a beautiful holly bush. Like most holly bushes, it had the usual assortment of glossy green prickly leaves--it was lovely, but not the kind of bush you'd reach out and touch.
But having just read/written about heterophylly, I took a closer look--sure enough, just as it says in the books, there was a distinct variation between the lower branches (which had been pruned extensively) and the upper branches (which had never been pruned). Even better--the right side of the bush had a slight overhang into a neighbor's yard. They clearly had been pruning there--on the right was an armada of sharp-tipped leaves.
However, on the upper branches, especially on the left (and unpruned) side, smooth edge leaves abounded.
As I wrote last week, the mechanism of holly heterophylly is pretty well understood. The prickly/smooth variations are a result of damage to the leaves. When the leaves are damaged (say, by a passing hungry deer or by a neighbor’s pruning shears), methylation of the DNA in the leaves happens as a result of tissue damage. (Side note: methylation is the process of adding methyl groups onto pieces of large molecules, like DNA, to modify their behavior. This is the way much of epigenetics works. When an animal chomps on a leaf, methylation happens.)
By comparing the DNA of prickly leaves vs. smooth leaves, it turns out the prickly ones were significantly less methylated than prickless leaves, suggesting that methylation changes are ultimately responsible for leaf shape changes. More methylation = more prickly leaves. What's more, the methylation has an effect on nearby leaves. Other holly leaves nearby will also develop the prickles, with the effect diminishing with distance.
I was delighted to see heterophylly in action while just strolling down the street.
Keep looking... and searching. Maybe you'll find more variation out there than you might expect.
