At the end of my last post I placed this image of this plant we found at the Charlotte Brody Discovery Garden at Duke Gardens:
...along with the promise that this would be the subject of my next blog post. So here you go:
Mimosa puidica - The Sensitive Plant
If you've never heard of this plant before, don't feel bad. I didn't really know about it until a week ago. This plant is something of a horticultural oddity, not having much ornamental value but instead is almost considered a novelty thanks to its tactile feedback. If you can find a garden center that sells the sensitive plant, it will most likely be inside, with the houseplants. Classified as a "pantropical annual" [1] ; it can be found in the tropic zone near the equator on multiple continents, though it can spread through the wild by reseeding. It's common enough as a weed to be annoying in Florida, Virginia, Maryland, and Washington D.C..
So what's it look like?
The 3-4 inch long leaflets are quite attractive and reminiscent of the fern fronds, which is where part of the plant's common name comes from. However, the attractiveness of the leaflets belies the overall aesthetic of the plant, which is low-growing, sprawling, somewhat sparse, and generally unattractive (in this author's opinion).
The flowers are small, less than one inch across, and a happy shade of pink. Interesting, but they don't redeem the plant by themselves:
So what's the big deal?
This, my friends, is the plant's major attraction:
Whee! How could you keep your hands off of it? After a few minutes, the leaves gradually reopen, ready for more fun. You could call a sensitive plant the Tickle Me Elmo of the horticulture world. Or not. Your prerogative.
These leaflets took about five minutes to reopen fully:
How does it happen?
On Mimosa pudica and some select other known plants, the leaves have special cells located between the leaf stem and , where it attaches to the branch, called the pulvini. The plant responds to touch by, in essence, depressurizing individual leaves and stems; causing the foliage to fold in on itself. [2] The science behind how exactly this happens isn't fully understood yet, though it does involve the rapid movement of calcium ions throughout the plant. [3] The why is also a mystery. It's possible the tactile response is a survival mechanism; Foliage that folds up is found less palatable to herbivores, so the sensitive plant is better able to survive in areas with lots of wildlife.The video and photos in this post demonstrate the sensitive plant's response to external physical stimuli. The plant's folding leaves can be called either seismonastic or thigmonastic, which are fancy words to call a response to shock or vibration. Venus Fly Traps and other plants rely on similar mechanisms. But what I wasn't able to capture for myself is that sensitive plants will also close up at night. These actions are called Nyctinasty [4], and are shared with many other plants.
That's a lot of real science contained in a so-called novelty plant, isn't it? Eight years after graduating with my degree in horticulture, I'm constantly amazed at just how complex and straight-up interesting plants are. Now if you'll excuse me, I've a whole host of cool terminology to look up!
Where to buy
Sensitive plants are supposed to be pretty easy to grow from seed, and you can order them from Amazon.com, conveniently enough: http://www.amazon.com/Sensitive-Mimosa-Pudica-Seed-Needs/dp/B00323LXCG
They're so fun, in fact, that where you see the leaves on the far right closed up again at 4:48... yeah... that was me. I just couldn't help touching it again. :-D
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