Several tree species in the United States have a curious way of propagating. They grow seeds with wings. When the seeds ripen, they fall from the tree and the wings provide lift that slows their decent. This allows them to be carried farther away from the parent plant. The winged seeds can range from less than a half-inch in length to more than 3 inches long.
Perhaps the best known of the trees with winged seeds, all species of maple produce such seeds in pairs . Each seed is called a samara. The samara has a relatively long wing compared to the size of the seed. Sizes range from relatively short seeds of the red maple to larger seeds of sugar maple, which can exceed 3 inches in length. Samara pairs are attached to each other along the leading edge. When the double samara is ripe, it splits apart and drops each samara separately. The samara falls with the characteristic "helicopter" pattern, spiralling to the ground.
Ash trees produce seeds that are less aerodynamic. Rather than having an airfoil shape, as do maple seeds, ash seeds are straighter, forming a lance shape with the seed on one end and the wing on the other. Ash seeds grow individually on a single stem. The seeds form in loose clusters. When ripe the seeds tend to fall in more of a fluttering pattern with some spiralling.
Many species of conifers, such as pine, fir, spruce and hemlock, possess winged seeds. When the cones high in the tree open, the scales of the cone lift up to release the seeds, which then fall out and are scattered by wind to propagate the plant. In some species, including the white pines, the seeds are strongly attached to the wing, while in other species, such as the yellow pine, the seeds are connected more loosely.
The least aerodynamic of the winged tree seeds, the elm seed is surrounded by an oval wing made of thin, papery material. When the tree sheds the seeds, they flutter along in the wind without any type of flight pattern at all. Elm seeds are relatively small and easily carried away as they fall from the parent tree by even light breezes.