Samaras of an ornamental maple, which I unfortunately cannot identify precisely. Probably Acer ginnala.
Interesting for me: The one-seeded fruits (samaras) with a membranous wing at one end, have typically a slight pitch (like a propeller or fan blade), causing the seed to spin as it falls. Depending on the wind velocity and distance above the ground, this seeds can be carried considerable distances away from the parent plant. The spinning action is similar to auto-rotation in helicopters, when a helicopter "slowly" descends after a power loss.
