Mimosas at Daybreak

On the 17^th of April Darwin was “botanizing” in the forests around the Socêgo estate. No diary entry today – just an entry labeled April 17^th and 18^th, presumably written on the second of the two days.  In it he writes:

“These two days were spent at Socêgo, & was the most enjoyable part of the whole expedition; the greater part of them was spent in the woods” (Apr 17/18)

Darwin spent some time collecting specimens and enjoying the forest, noting poetically:

“Thus it is easy to specify individual objects of admiration; but it is nearly impossible to give an adequate idea of the higher feelings which are excited; wonder, astonishment & sublime devotion fill & elevate the mind.” (Apr 17/18)

Ah, to be a naturalist in a new land – a place where everything is so unique that words fail to describe the feeling of excitement. What a wonderful concept.

During his wandering, one plant that catches his eye is the mimosa – a name that refers to a genus of plants in the legume (Fabaceae) family.

“If the eye is turned from the world of foliage above, to the ground, it is attracted by the extreme elegance of the leaves of numberless species of Ferns & Mimosas.” (Apr 17/18)

Mimosa pudica from an 1880/3 book by Francisco Manuel Blanco:

In Voyage, Darwin expands on one of the more interesting aspects of certain species of mimosa – in particular, the Mimosa pudica.  He writes:

“[Mimosa], in some parts, covered the surface with a brushwood only a few inches high. In walking across these thick beds of mimoæs, a broad track was marked by the change of shade, produced by the drooping of their sensitive petioles.” (Voyage of the Beagle)

Mimosa pudica has the ability to rapidly react to heat or touch. In fact, in some ways it almost looks like it has “animal-like” reflexes. However, mimosas don’t have a nervous system (that would be pretty cool but no such plants exist on Earth).  Instead they react by releasing chemicals (including potassium ions) into the cell that rapidly changes its water content and causes it to collapse.

As the cells collapse they “pull” surrounding cells inward causing the leaf to fold up. (Think of each cell like a stretched rubber band – as the rubber bad relaxes, it “pulls” together.) I’ve said it before and I’ll say it again – the natural world has some pretty cool stuff!

Mimosa pudica reacting to touch (from Wikipedia Commons):

Here is another video of mimosas reacting to heat.

Another species of mimosa (Mimosa tenuiflora) is know for the psychedelic compound – dimethyltryptamine (DMT) – found in its roots. Luckily Darwin was not tasting plants today.

And to think, I always thought of mimosas as a mere drink!  Though to be fair, the drink is not entirely unrelated to the botanical world. It may have been named after the orange-yellow flowers of a different legume – Acacia dealbata, a common name of which is a Mimosa. (RJV)

Advertisement