Note: Do not rely on this information. It is very old.
Samara, a dry winged syncarpous fruit. It may be. single, as in the ash, elm, or birch; or double, or rarely triple, as in the maples, and the wings may be lateral or almost all round the seed-cavity. Though the double samara breaks in half, it does not, whether double or single, split so as to disclose its seeds. The wing serves to disperse the contained seed away from the shade of its parent plant, those of the sycamore spinning round in the wind when falling from the tree like a screw-propeller. The wing in this and similar groups is sometimes elaborately shaped like a screw-propeller so as best to serve this purpose.