Wind dispersal enables seeds to be taken away from the parent tree to reduce overcrowding – the UK’s recent hurricane weather will certainly have assisted this! However, it does run the risk of seeds falling on less optimal ground, especially in human areas dominated by concrete and other hard surfaces.
To increase their dispersal, some seeds form structures to catch the wind and aid their flight. This is done by extending the fruit wall to create fibrous tissue around the seed, forming a 'wing'. Winged seeds are called samaras (also known as keys or helicopters) and are used by many tree species, such as field maple, Acer campestre.
Samaras were studied to aid the design of helicopters; particularly those from the sycamore. If tossed in the air they spin around in the wind, giving them the nickname spinning jenny. Other nicknames include whirligig, whirlybird and wing-nut.
Tree seeds are a valuable food source for many types of woodland wildlife, particularly finches, tits and small mammals.
Seeds dispersed by wind
Trees with winged seeds:
- Ash, Fraxinus excelsior - is the third most common tree in Britain (but is under threat from ash dieback) and has clusters of winged seeds, often called keys
- Common Lime, Tilia x europaea - can live over 1000 years. Its seeds are held in clusters with a single wing
- Hornbeam, Carpinus betulus - can reach 30m in height. Its seeds have a 3-lobed bract
- Sycamore, Acer pseudoplatanus - is not a UK native but is widespread and can grow very quickly. Over 10,000 double-winged samaras a year can be produced by this tree
Some smaller plant species such as rosebay willowherb, Chamerion angustifolium, dandelion, Taraxacum officinale and thistles, Cirsium species, also use the wind for dispersal. They have downy hairs or parachutes and are often seen floating around at this time of year.