Sensitive Plant and Mimosa

The Sensitive Plants (Mimosa microphylla Dryand.) are back in bloom. This little plant goes by many names but mostly it is categorized as a noxious weed in Florida. I guess its all in the eye of the beholder. I find them to be quite whimsical.

This plant undergoes changes in leaf orientation termed "sleep" or nyctinastic movement. The foliage closes during darkness and reopens in light. The leaves also close under various other stimuli; touching, warming, blowing, or shaking. The movement occurs when specific regions or cells lose pressure and chemicals including potassium ions are released which force water out of the cell vacuoles, causing the cells to collapse.

It is not known why this subfamily of plants evolved this trait but one could assume that the motion would discourage predation by animals that might be frightened by the rapid movement. It could also be effective in dislodging insects that might choose to dine on its leaves.



I'm not sure which one this is. I can say for certain they are in the Pea family (Fabaceae) and I wish I could get them to grow in my yard. They apparently come in on imported sod. as they appear distinctly related to sodded lawns. . . something we have never attempted.

The USDA lists 10 synonyms for this plant. They all look more-or-less the same to me. They have deep green foliage that retracts when touched and they sprout these powder-puff-like blooms in early summer. They are tiny. I didn't put my finger in any of these shots for scale . . . but the end of my finger is about as big as the blooms.



Meanwhile the other noxious weed called "Mimosa" is in bloom in Florida. Its a much larger specimen. . . and without the cool rapidly retracting leaves. Mimosa (below) is actually Albizia julibrissin Durazz. . .also known as Silk Tree.



Albizia spp. are also in the Pea family and also not native to Florida. They are a fast growing tree that is amazingly durable. Despite the current extremely dry conditions they are in full bloom.



Below: Mimosa pudica retracting when touched.