Nature on our Doorsteps: Sycamore helicopters

Rosaleen Dwyer is the County Heritage Officer at South Dublin County Council – every week she gives us an insight into nature on our doorsteps and the beautiful biodiversity of its plants and wildlife.

THE Sycamore tree is a familiar feature in our parks, hedgerows, and along roadsides. It is native to central and southern Europe, but it has been widely planted in Ireland since the 17th century as an ornamental species.

It is tolerant to air pollution, so it is frequently planted as a street tree in cities. Sycamore’s seeds are the well-known winged ‘helicopters’ or keys, that twirl and float in the air when the autumn winds blow them from the tree.

The scientific name for the helicopter seed is a samara.

Samaras are a type of dry, hard fruit where part of the fruit has extended out to form a flattened wing of papery tissue.

With other trees like Elm, the seed is placed in the middle of a flat, papery, circle of tissue.

With Sycamore, the tissue is tougher and more fibrous, and it is stretched out sideways to form something that looks like a helicopter blade.

Sycamore’s samaras occur in pairs.

They are connected together at the hard seed end, with the fibrous wings held out to the sides at an angle.

The seeds usually separate as they fall from the tree.

Scientific studies have shown that as the winged seed drops, the heavy part of the seed falls head downwards.

As it twirls down through the air it creates a vortex above itself, just like a tornado.

The effect of this vortex is that the air pressure over the upper surface of the seed is lowered.

This has the effect of drawing the seed back upwards into the air, allowing it to travel much further in the wind away from the parent tree.

The engineering principles behind the flight of twirling seeds like Sycamore have inspired improvements in designs for modern helicopter rotors.

Bunches of seeds are noticeable in Sycamore trees at the moment as they mature, turning from their summertime green-tinged-with-red to their autumn colour of brown.

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