What a funny question. Why should plants sleep? Just like us, they need to conserve power, reduce water consumption and also snuggle down to keep warm and away from predators I suppose. No, seriously, its true. Plants have circadian rhythms just like us and this is reflected in how they control their leaf movements. Of course not all plants make it that obvious. If you’re in the tropics, Rain trees exhibit this behaviour very clearly (oh all those Biology classes come flooding back to me now) and it is a delight to observe the leaves fluttering in the wind in the daytime but hanging droopy and tightly closed in pairs at night, giving the tree a melancholic, sparse appearance.
I didn’t think much of this until recently when I’ve been observing my little durian plant SS No. 1 at night. Initially, I was under the impression that I was depriving it of water which is why the leaves were so droopy. But I knew this wasn’t the case as come morning, the water could be clearly seen and felt as the soil was indelibly wet. Hmm, what could it be? I decided to use my empirical powers over the course of a week to ascertain if it could be that durian plants have circadian rhythms.
In the olden day magicians’ tone of voice: OBSERVE!
The photo on the left was taken at approximately 10:30 am and you can see how the Durian plant responds so well to the morning sunlight.
The photo on the right was taken at 11:30 pm at night* and you can see how the leaves have flattened themselves against the stem. Even if you try to lift the leaves, you can detect the tension in the branches curling the leaves inwards.
* Photo has been lightened up considerably as it was quite dark and taken without flash.
OK, I know its not exactly the same perspective but I turn the pot around frequently and forget which angle I took the photo of SS No. 1 last time. Despite that, you can tell that the leaves are extended out in the daytime and huddled in at night.
It is interesting that the leaves do not close (fold in half) at night and are merely pulled in to lie almost flat against the stem. The angle and degree of extension and contraction seem fairly significant. Plant circadian rhythms have been extensively studied but I’m not sure if anyone has ever studied it in Durians. It would be wonderful if I’m the first to describe it with pictures here. 🙂