A germinating seed of sycamore, Acer pseudoplatanus. The picture shows a single seedling about to emerge from its split seed coat. The green folded tissues are the cotyledons of the embryo; the curved filament below them is the hypocotyl, a stem that terminates in the root (not visible here). The feather-like wing (above) shows weathering due to being on the ground over winter.Sycamore seeds are winged achenes (single-seeded fruits) known as samaras. Usually produced in pairs, they can be carried considerable distances on the wind when shed. Sycamore is native to central and eastern Europe and west Asia. It was probably introduced into UK in the 16th century as a timber tree. As a prolific seed producer it is now the most widespread and common neophyte tree in Britain, often regarded as a pest species in the wider environment