The Prayer plant comes by its name well: every night, this unusual plant folds up its leaves. Some plants simply tilt their leaves upwards, whereas others will actually go so far as to curl up their leaves as well. When daylight returns (or someone turns on the lights in the office), the leaves fold down to their normal orientation. Here's a cool time-lapse video of the process in action.
Houseplant care sheet: Prayer plant
Low light level requirements make this a great office plant.
Prayer plants are non-toxic to dogs and cats.
Prayer plants tend to be compact and somewhat slow growing. Keep this in mind when choosing a Prayer plant: don't buy a too-small one, thinking that it will grow into the space.
This is also something to keep in mind when thinking about repotting a Prayer plant. Too big a pot is wasted on this slow-growing plant. Never re-pot a Prayer plant before it is time; the plant probably will not grow into it, and the soil will turn compact and rock hard. Odds are good that you will never need to repot your Prayer plant - I have had happy Prayer plants for years which never grew enough to warrant being repotted.
The Prayer plant (Maranta sp.) is native to the deep forest and jungle floors of Central and South America. This makes it almost ideal for many homes and offices, because it has very low light level requirements.
If your Prayer plant's leaves begin to turn brown and curl up, it may be receiving too much light. Always keep Prayer plants out of direct sunlight.
The one area where Prayer plants can be difficult to keep is their humidity requirements. As jungle plants, Maranta are used to high humidity levels.
If your plant is situated in an area without strong air currents, a pebble tray is the way to go. Fill a shallow dish with pebbles, add a bit of water, and set the plant atop the pebbles (but not in standing water).
If your plant is in air currents, for example if your desk is near a heating vent, the pebble dish won't be useful. You will need to mist your prayer plant regularly, at least once or twice a day.
Prayer plants are one of the few plants that prefer soil which is always damp. These plants are a good choice for those self-watering pots where you water the plant by pouring water into a little divot at the bottom of the pot. Many plants dislike the effect of constantly standing in water that these self-watering pots provide, but Prayer plants love it.