Nyctinasties, according to John Ben Hill (in 1936), “are the most common nasties.” Like all nasties, they don’t care where what they’re reacting to comes from – that’s what sets them apart from tropics.

Ah, tropics! Who – or what – doesn’t love following the sun? I’ll tell you: these nasties don’t. They don’t care which direction the sun goes, as long as it goes away. That’s why they’re nyctinasty. During the day, everything’s lain flat, basking in the sun, but when night comes, the blades flip up. As Peter V. Minorsky said (just last year), “the vertical orientation of the blades … would be especially beneficial to flying nocturnal predators … whose modus operandi is death from above.”

Which, in its way, is quite cooperative. Just as long as you’re not a nocturnal herbivore, suddenly exposed to bats, owls, and other flying threats to your life. But the death-dealers surely like it quite well.

Perhaps I should shed a little more light on the subject. Nyctinasty is not related to the nasty that you’ve probably used on occasion to refer to perfumes, politics, movies, music, sex, clothing, and potluck contributions. Nor does it have anything to do with NYC, the city that never sleeps. No, it comes from nycti–, which refers to night and traces to Greek νύξ nux ‘night’, and German nast–, from Greek ναστός nastos ‘pressed together’, which in German and English botany refers to a non-directional influence on a plant. A directional influence, you see, is tropic, as in heliotropic, ‘turning towards the sun’, like sunflowers. A nasty is an influence that is directionally indifferent. A nyctinastic plant – one that exhibits nyctinasty – changes the orientation of its foliage at night, but it doesn’t pay any heed to exactly which way the sun went. Just as long as it’s gone.

People, during the day, are mostly vertical, or at least upright of torso, and at night – for at least the heart of the night – usually go horizontal. Nyctinastic plants are the opposite. Their leaves and petals splay wide open during the day, basking as though on a beach. Then they shut up shop when the sun goes down: as Minorsky says, “At night, the positions that the leaf blades assume, regardless of whether they arise by rising, falling or twisting, are essentially vertical.”

But why? Why not just stay as they were? Are they afraid of muggers, or of mugginess, or of nightmares, or of night rabbits? Minorsky lists some usual hypotheses:

Among the ideas put forth to explain the raison d’être of foliar nyctinasty are that it: (i) improves the temperature relations of plants; (ii) helps remove surface water from foliage; (iii) prevents the disruption of photoperiodism by moonlight; and (iv) directly discourages insect herbivory.

But then he sets forth another, which I have already mentioned: to blow the cover of creatures that go “munch” in the night. To all the plant-eaters that want to sneak out and dine at fashionable hours, these plants say “Surprise! You’re nicked, my nasties!”

Of course, it’s up for debate who are the nasty ones. The herbivores are just out for a late-night salad, and salads usually stay put. These ill-behaved greens don’t play along, and as a result, there will be blood, and bats, and owls. Ichneumon wasps, too.

Oh well. Nature is ever red in tooth and claw – and blade, too. It’s bedtime now. Pull your sheets and blankets snugly over you. I’m sure they’ll stay in place and keep you safe from even the most common nasties. Sweet dreams!

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