Example of the leaves at night.

Maranta leuconeura

i think the term is photo-sensitivity ...

its not all that uncommon .... they spread there leaves so as to collect more light to photosynthesize ... aka .. feed themselves ...

and.. being sick.. of course.. i cant think of another example... lol ... i guess its like a sunflower that follows the sun during the day ...

ken

"Nyctinasty (nyc = night or darkness, nastic = firm or pressed close) is the specific movement of leaves or flowers in a daily pattern, open during the day and closed at night.

Nyctinastic movements are accomplished by the flow of water in and out of specific cells in the pulvini (swellings, singular is pulvinus) at the base of the petioles (the stalk that attaches the leaf blade to the stem). It is not unlike our muscle movements in that there is an extensor and a flexor pair. When K+ and Cl- are pumped into the extensor cells on the bottom of the pulvini, they become hypertonic and water follows the ions through osmosis. This causes the extensor cells to swell due to increased turgor pressure."
- http://biologicalexceptions.blogspot.com/2011/11/plants-that-dont-sleep-will-take-dirt.html

"A pulvinus is also sometimes called a geniculum."
- https://www.boundless.com/biology/definition/pulvini/

It's common name is Prayer plant.

Thanks for all the information. I've recently started collecting houseplants in a serious way and I need all the help I can get.
The little maranta is not in an idea spot, sort of drafty and cold.

I'm going to do some research on nyctinastic plants too, fascinating. Thanks again.