At the most recent UC Davis Arboretum plant sale, I finally found a specimen of a plant I’d wanted for as long as I can remember: Mimosa pudica, commonly called “sensitive plant,” “humble plant,” “shameful plant,” or “touch-me-not.”
I can’t remember where I first saw one, but many botanical gardens have specimens they allow visitors to interact with. Kids—young and old—are drawn to them like moths to a streetlight. If you’ve never experienced a sensitive plant, you probably wonder why it’s so special. Take a look at the animation below which I found on Wikipedia:
|Image source: Wikipedia|
Yep, you touch a leaf, and it folds up as if by magic. This action is called “seismonastic movement,” and it has to do with a loss of turgor pressure in certain cell regions. If “turgor pressure” is up your alley, you can read more about it here.
There are various hypotheses as to why Mimosa pudica does this; the one that makes the most sense to me is that it alters the shape of its leaves to confuse herbivores who might pass it by in favor of a plant with more normal-looking leaves. Whatever the reason, it’s fun to poke a leaf and watch it get going.
When I mentioned to my mother-in-law that I got a mimosa, she thought I was talking about the mimosa or silk tree (Albizia julibrissin). This popular (and relatively hardy) tree is indeed a distant relative and has similar leaves. Like Mimosa pudica, its leaves close at night (a phenomenon called “nyctinastic movement”), but unlike Mimosa pudica, they don’t fold up when touched (the aforementioned “seismonastic movement”). I hope you’ve committed these terms to memory because there will be a quiz tomorrow!!!
Mimosa pudica is not only sensitive when it comes to its leaves, it’s also sensitive in terms of the weather. This South and Central American perennial is extremely tender; it appears to dislike temperatures much below 55°F and definitely needs to be brought inside in the winter. Together with the Socotran cucumber tree (Dendrosicyos socotrana) I also bought at the Arboretum sale, it will be a houseplant living in my home office.
|My weird and wonderful mimosa|
|Hairy and thorny to boot!|
|Same leaf as above in the midst of a seismonastic movement |
(that’s “folding up” to you and me)
|Puffy flowers are an added bonus|
|All in all, a neat package…|
|…I find hard to resist|