SEED DISPERSAL

Do you know that seeds like travelling?

Have you ever thought that seeds have a traveller's spirit? Yes it's true but they don't travel for pleasure. Seed travels are called dispersal and they give seeds the opportunity to find good growing conditions. Often germination close to the parent is a disadvantage because of overcrowding the existing plant and reduced light and soil nutrients therefore seed dispersal increasing plants' chances of survival.

Seeds disperse in four main ways, by air, water, animals and self propulsion:

1. Wind dispersal

Wind can carry seeds away from their parent plant. Many wind dispersed species have parachute-like structures to maximise the length of their dispersal. The Eurasian dandelion (Taraxacum officinale) and numerous other plants from the Aster family (Asteraceae) have this type of mechanism. Their "parachutes" are formed by hair-like growths that can carry the seed over great distances. Other wind dispersed species have seeds with wings. Some act like miniature helicopters. The Maple Family (Aceraceae) has very successfully evolved this method. Seeds typically have a rigid or membranous wing at one end. Nature has cleverly designed the wing with a slight pitch (like a propeller or fan blade) enabling it to spin increasing its ability to move through the air as it falls.

2. Water dispersal

A few species use water to disperse their seeds. Seeds drop from the plant into water and float until they reach land. If they find a suitable location they will germinate. A good example of this method is the coconut which can remain in the sea for a considerable time before washing ashore.

3. Animal dispersal

Animals find fruits a rich source of food and as a result aid seed dispersal. Digestion degrades the juicy part of the fruit often leaving the seeds intact. These are excreted in droppings often great distances from the parent plant. Some animals disperse seeds on their fur. This is the case for burdock (Arctium). It has seeds with minute hooks that 'stick' to animals as they pass. Humans are also major dispersers of seeds, next time you go out into a field check your clothes and you will surely find these little travellers!

4. Explosion

Plants can be very surprising for example the pods of the squirting cucumber (Ecballium elaterium) explode like little green bombs shooting the seeds long distances. Explosion ensures seeds do not fall close to the parent plan.

© ENSCONET. European Native Seed Conservation Network