How Plants Count



Flickr John (CC)

Why are four-leaf clovers considered lucky? Because four-leaf clovers are rare. Why are four-leaf clovers rare? Because almost all clovers have three leaves. This is the most elementary example of Fibonacci numbers at work in botany. It’s really difficult to find plants that have 4 petals or leaves. Most have 3 or 5. Or 13 (like the ragwort). Or 21 (like black-eyed susan). Or 34 (plantains). And while not all plants in those species have those exact numbers of petals in every example, they’re always very close and the average for that species is always the associated Fibonacci number.

It’s not just plant petals. The seed heads of daisies and sunflowers have swirling rows, and in the case of the sunflower there are 34 rows in one direction and 55 in the other. Those are oddly specific numbers, aren’t they? One might expect that for smaller plants it would be “easy” to land on a number like 3 and 5 with some regularity. But 55? 89? It starts to feel like there’s a purpose behind these numbers.

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