— Active | Passive

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.