Plants that Move

 My 'Little Tree Plant'

Plants are moving all the time. Most move so slowly that we can’t see it, unless the wind is blowing or we brush past them. 

Many plants also have leaves that move on their own. Leaves will turn to face the direction of the sun, which is a slow gradual process. Some plants move for different reasons like distracting animals that might want a nibble.

A lot plants have leaves that curl up or roll down under stressful conditions like drought or cold, but recover afterwards. Hardy rhododendrons lose most of their moisture and both curl and hang limply all winter, yet recover fully when spring returns. It’s thought this habit helps keep frost crystals from forming and damaging leaf cells.

I had a prayer plant (maranta) which used to fold its leaves up at night, which I found fascinating. This effect is something called nyctinasty which is common in some plant families, such as the legume and oxalis family. Even the clover in your lawn does the same thing.

The movement is caused by a hinge-like structure at the base of the leaf or leaflet called the pulvinus that is filled with water during the day, but drains at night, so that the resulting lack of turgor (pressure in the cells) causes the leaf to fold.

Reacting to Touch

This brings me to my latest shopping purchase. I have bought two types of plants that have moving leaves, but this time, when they are touched their leaves fold up and collapse. I have bought some Mimosa pudica seeds to grow on and three ‘Little Tree plants’ (Biophytum sensitivum)

The phenomenon of plants that react to touch is known as thigmonasty or seismonasty, and occurs when something touches or shakes the leaf. And some will also react when you hold a match up to them. This is usually rapid and is certainly visible. 

Touch Me Not

The Mimosa pudica is a legume and also known as sleepy plant, touch-me-not or shy plant. They are short-lived houseplants and can be a weed in tropical countries where they originated. A light touch causes a single leaflet of the leaf to fold inward, a firmer touch will lead to the whole leaf drooping and shaking the plant will cause all its leaves to collapse. If you run a finger down the leaf, the leaflets will close like dominoes. They are easy to grow from seed so I’m having a go myself.

Little Tree Plant

Less well known is the little tree plant (Biophytum sensitivum), a small herbaceous houseplant that looks like a tiny palm tree and is sometimes used as a tree substitute in terrariums and fairy gardens. It is modestly touch sensitive, but its leaves move all on their own much of the time, albeit quite slowly. I couldn’t find the seeds so ended up buying three plants from an orchid grower in the Netherlands.

The plant originates from India and South Africa, where it can be found growing in wet, boggy soils near streams and waterfalls, where it is shaded by taller trees and shrubs. I thought it would live quite happily in the bathroom. The plant seeds are over a Euro each to buy so I will be collecting my own from these mature plants. The star shaped pods formed after flowering explode and can scatter the seed over a metre so I will need to either cover the plant with a fine mesh (think sandwich cover on a picnic) or encase the pods in plastic bags to collect the seed, there are a lot of flowers on the plant so even if I have to get the dustpan and brush out I’ll be sure of getting some to grow on.

The leaves of the little tree plant fold downwards and the stems rise at night. It’s said the plants produce many healing compounds and are widely used in Indian, traditional and Western medicine. They are usually grown as annuals.

Insectivorous plants

The other group that includes plants sensitive to touch are carnivorous plants or, more correctly, insectivorous plants.

The best known of these is the Venus flytrap (Dionaea muscipula), often offered as a houseplant, although rarely very long-lived in the average home environment. I’ve tried to grow these before but find they rot easily. It might be the house conditions or the fact that I keep prodding the fine hairs in the trap with a pencil to see it closes up. 

My resurrection fern (Pleopeltis polypodioides) is the hardiest sensitive plant I ever owned. It survived without a drop of water all scrunched up for years in a drawer, I watered the apparently dead fronds and they became completely green and opened up within a day after a good soaking.