A handful of plants in the home gardening world are treasured for their somewhat unique behavior.
These plants belong mainly to the sister genera of Calathea, Goepperia, and Maranta, all from the Marantaceae family.
What makes these plants so striking is that their leaves fold upwards at night in a prayer-like pose.
This has earned them the common name of prayer plants.
But why exactly do these plants do this, and how?
Why Do Prayer Plants Pray?
There are many theories on why prayer plants have their unique movement, beginning with the underlying mechanical explanation of nyctinasty.
We’ve included the most popular theories, as the proper explanation may combine some or all of these.
Before we get into the “why,” let’s take a moment to understand the “how” behind the prayer plant movement.
The term “nyctinasty” refers to movements triggered by light levels.
These movements allow a prayer plant always to have its leaves positioned to get the most light and therefore have the most efficient photosynthesis.
However, theories regarding why a prayer plant has developed this mechanism extend far beyond simple light-gathering. This doesn’t explain why they fold into a closed position at night when the light is at its lowest.
This movement constantly occurs throughout the day, often so subtly that you never notice it.
As plants lack muscle tissues, prayer plants have developed a unique joint at the base of their leaves called a pulvinus.
This joint is made of special cells which can swell or shrink depending on how much water is present.
When specific cells swell, it creates pressure that shifts the attached leaf to a new position.
Theory: Protection From Fungal Infections
This is one of the more practical theories out there.
Most plants have leaves that remain open at night. This allows rain and dew to settle on the leaves.
This moisture evaporates more slowly as it’s cooler at night, inviting fungal spores to infect the wet leaf.
Additionally, the leaves’ movement can cause water to run off the leaf, further protecting it from fungal infections.
Of all the existing theories, this is perhaps the most widely accepted.
Theory: Temperature Regulation
This is another popular theory that looks at simple practicality for an explanation.
Think about what you do when you’re cold.
Do you stretch yourself out or curl up in a ball to stay warm?
This is why the scrotum in mammalian males expands and contracts, as the testes require a specific temperature range to produce sperm.
This is why temperature regulation is a popular theory.
Supporters argue that folding the leaves at night when it’s cooler helps the plant conserve heat, and by opening up further when it’s warm, there’s a larger surface area to vent excess heat and aid in transpiration (the plant equivalent to sweating).
Theory: Moisture Retention
While this theory goes hand-in-hand with the first theory we mentioned, it’s less popular.
According to this theory, the leaves open up to catch rainwater, then close at night to reduce evaporation.
This theory isn’t as popular because it seems to contradict transpiration.
Transpiration is a process in which a plant excretes more than 97% percent of the water it absorbs through particular pores in the leaves.
The resulting moisture evaporates, increasing humidity levels around the plant, similar to how our sweat cools us off in hot weather.
If the plant opens its leaves to absorb water while also actively sweating the water back out, there’s no need for both processes to coexist.
Theory: Insect Defense
Although this theory cannot be ruled out as a potential bonus for the prayer plant movement, it has its fair share of problems.
According to this theory, prayer plants close their leaves at night to make it harder for insect pests to feed off of them.
While it certainly reduces the potential surface area, most piercing insects feed off the bottom of the leaves, which are the parts of the leaves left exposed at night.
However, it could be argued that this is intentional, as the whole reason aphids, mealybugs, spider mites, and other pests prefer the undersides of leaves is to help them hide from predators.
By folding up at night, those delicate undersides are in full view for any ladybug, parasitic wasp, or other hunters that happens to pass by.
Of course, this would also leave the prayer plant’s leaves more susceptible to chewing insects such as grasshoppers and caterpillars, as they now have easy access to not one but two leaves at once.
The Theories vs. Reasons They Won’t Pray
Sometimes a prayer plant refuses to pray, and these reasons have a lot to do with the theories of why they pray in the first place.
For example, the mechanism relies on light to function, so a lack of light will prevent the plant from opening up.
Conversely, too much exposure to direct sunlight can scorch the leaves, trapping them in an open position.
One of the reasons the fungal theory has so much support is that the leaves won’t fold if there’s not enough water or humidity.
If the plant folds to reduce the risk of fungal infections, it stands to reason that the leaves won’t fold in a situation where that risk is no longer present.
Of course, if the plant is dehydrated enough, this could affect its ability to pray since the mechanism relies on water filling the specialized cells.
Finally, note that your prayer plant has a habit of “forgetting” to pray when stressed – just like you and me.
So if your prayer plant isn’t behaving normally, check to see if anything in its environment has changed or if the plant is sick.
In most cases, addressing the change or illness will have your prayer plant usually praying again within a few days.