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.
