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.
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