Like a soap bubble

I just returned from three weeks of botanical surveying in the forests of Costa Rica. I’ll write more about the trip – and what we found – in my next post, but for now I just want to share this lovely image. The plant you’re looking at was described to me as ‘una hoja plastica’, or a plastic leaf. It really does look a lot like a plastic fern leaf if you hold it, but the most incredible thing is the way it shimmers in the light, turning this eerie shade of iridiscent blue-green at the correct angle. And the effect goes away in direct light – hold it up to the sun and it looks like normal, average, green leaf. What’s going on? This leaf is so thin it’s just one cell thick in most places, which means it’s thin enough for us to see thin-film iridescent effects. As light bounces through the leaf it interferes with itself, only reflecting certain colors at certain angles. It’s the exact same thing you see in hummingbird feathers or a soap bubble. Who knew plants did it too?

An interesting follow-up question is why this plant has such thin leaves. Many ferns have thin leaves, so it may be a constraint of the species’ evolutionary history. But it may be adaptive, too. I actually know very little about fern biology, but suspect that it has to do with how water is distributed in the leaves of these evolutionarily old clades. Their plumbing isn’t especially advanced. What do you think?

And just to compare – here’s an image of iridescence in a green violet-ear hummingbird, also from Costa Rica!

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