Plants that move?!

by Kealey Bacic

Kealey has her own business, Iron Ivy ( where she spends her days designing homewares inspired by the natural world and is a horticulturist dabbling in greenhouse jungles.

Nyctinastic movement, a plant's daily slow dance. Unlike you or I, or most animals on this planet for that matter, plants are considered to be the most stationary as far as organisms go. But some plants have pretty magnificent capabilities that allow them to display a range of movements; from slower than paint drying to rapid movements too fast for the naked eye to observe.

 The Mimosa pudica displays both a slow closing of its leaflets upon sunset and reopening at dawn as well as a rapid closing movement upon sensing touch. Both of these responses are caused by external stimuli, meaning the plant doesn’t just move around willy nilly but rather it reacts to changes in its immediate environment. Likewise, plants in the Marantaceae family display a dramatic opening and closing like clockwork every day.

A timelapse captured of species from the Marantaceae family.
A great example of Nyctinastic movement with the plants leaves
moving as a direct result of the sun/light. 

Nastic movement is the physical response of some plants to external stimuli. This characteristic is seen in plants responding to light (nyctinasty) or touch (thigmonasty). Nyctinastic movement is the term specifically relating to movement in response to daylight/darkness. A plant moves following a circadian rhythm, typically associated with sleeping and waking. No definitive answer has been provided as to why some plants exhibit this behaviour, but there are a few strong hypothesis’;
1. It improves the temperature stability of the plants when ambient temperatures drop.
2. It helps remove water from the leaf surface, minimising fungal disease.
3. It prevents the disruption of “photosynthetic rest” by moonlight
4. It discourages insects from inhabiting and or eating the plant
5. It reduces the overall size of the plant making it less attractive to nocturnal herbivores.

We may not know why, But what about how plants make this daily movement occur without muscles or nerves? This incredible movement is all thanks to a part of the plant called the pulvinus. Bear with me here, this is the part where things get a little technical… Pulvīnus is Latin, meaning “cushion like, pillowy. The pulvinus on a plant is a swollen, joint-like cluster of cells, located at the base of the leaf where it meets the petiole or stem. The pulvinus does its thing using two different types of cells; extensor cells which are located on the upper side of the pulvinus, and flexors located on the underside. During leaf opening, an increase in turgor pressure in extensor and decrease in flexor cells, causes the leaves to move downwards and sit horizontally, the pulvinus “joint” now bent like a knee. When closing, the inverse occurs, extensor cells shrink, and flexor cells swell, moving leaflets upward. It’s pretty clever stuff, amazing in its intricate yet seemingly simple design.

Regardless of why or how plants exhibit this daily movement it is a fascinating quality that seems to humanise the plants and give them personality. Plants within the Marantaceae family such as Goeppertia (formerly Calathea) and Maranta have become hugely popular houseplants over the last century and have been affectionately nicknamed “prayer plants” as their daily slow dance is reminiscent of a sun salutation. The Mimosa pudica has been affectionately called the “sensitive plant” because of its reaction to shying away from touch. Although I guarantee you it’s not actually a shy plant…given the right conditions this plant will spread itself far and wide, densely smothering tropical understories. While these plants don’t actually have any emotional or capabilities responses we do find ourselves gravitating towards plants with a little bit of character and being able to dance is certainly a quality we humans tend to find appreciation in.