— Active | Passive

By: Amir Shahrokhi
18-01-2011
Systems Research
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The Oxalis Triangularis is a great example of a plant that exhibits photonastic behaviour, that is one that produces a mechanical response to changes in light levels. As opposed to (photo)tropic movements which require direct light, nastic responses are due to changes in diffuse levels.

The reaction is made possible by changes in the osmotic potential of cells of the pulvinus at the base of the leaf, a chemo-mechanical process. In addition, the plant also exhibits interesting growth behavior in the formation of the canopy; the larger leafs occurring at the top of the canopy, but organised in such a way that they allow light penetration to the smaller leaves below.

"Turgor Pressure: also called turgidity, is the main pressure of the cell contents against the cell wall in plant cells. Turgid plant cells contain more water than flaccid cells and exert a greater osmotic pressure on its cell walls.

Turgor is a force exerted outward on a plant cell wall by the water contained in the cell. This force gives the plant rigidity, and may help to keep it erect. Turgor can result in the bursting of a cell." Steve Nix

Oxalis Triangularis

The dynamism of the Oxalis is an effort to balance water consumption (used to spread its petals) with maximizing solar exposure (needed for photosynthesis).

Diagram of turgor pressure on plant cells; the mechanism by which the movement of the plant is accomplished.

A Grasshopper simulation model of the Oxalis Triangularis. The three petals of fold downward from a common point at the end of the stem and in turn each leaf (bi)folds in on itself as the edges of adjacent petals approach each other. This hierarchically linked motion exhibits a deceleration of the macro mechanism while the inward folding mechanism of each petal is accelerated.

A Grasshopper simulation of the above model exhibiting light exposure on the individual faces of petals throughout the day.

Plan view of above model

2 comments
  1. Project 3: | Physical Computing says: March 18, 201412:56 pm

    […] happens due to changes in osmotic pressure (1).  A video of the plant movement is given here:  http://amirshahrokhi.christopherconnock.com/2011/01/18/43/. Oxalis Triangularis […]

  2. RMAU says: June 3, 20166:47 pm

    Three is often the magic number when it comes to Oxalis . The most common species grown as a houseplant is

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