Offset causing asymmetry at the leaf base

what causes this asymmetry of leaf base? I see it a lot now in Solanes, especially in Datura
and Brugmansia

I seems to neatly follow a secondary vein.


It’s a common characteristic in many species and is often used as one of the identifying features. Tilia (basswood/linden/limetree) & elms are examples of common North American and European trees that also have this trait, but examples can be found all around the world. It’s generally called an “uneven leaf base”.

I’ve never come across a reason for it, but if I was forced to hazard a guess I’d suggest that it has to do with stress relief. Many plants have leaves that have one side larger than the other, flattened petioles, or something similar. These features are often thought to promote the predictable relief of stress by wind or rain by facilitating the twisting of the the leaf to dump water or allow wind to slip by.

It’s possible that the uneven leave base serves a similar function.

At the same time perhaps it also serves to provide support as well, much like a buttress on a cathedral, as the side being shorter would potentially be stiffer, allowing for more leaf rigidity in non-rainy/windy situations.

Those are guesses though as I said I’ve never seen a reason proposed for this particular common feature of many plant species.


We might just as well ask why plants have symmetrical leaf bases. It’s not intuitively obvious, at least, that one is necessarily the default and the other requires explanation.

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the aerodynamic advantage seems to be very plausible. Ever since noticing this feature, I can sum it up, so far, that the leaves with this asymmetry are healthy, display no developmental deformities, no sign of insect presence or attack.

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