Researchers at the University of Maryland studied the aero-dynamics of a maple leaf and used their findings to create and optimize a high-performance Micro Air Vehicle. Early results show that this 2 DoF MAV can potentially outperform more complicated helicopter and ornithopter style MAVs.
The following video shows the most recent work, showing its high performance and controllability.
From the creators:
The culmination of 3.5 years of research has led to controllable monocopter that can autorotate like a maple seed (Acer diabolicum Blume) and fly like a helicopter (hover and forward flight). The vehicle, invented at the University of Maryland, Aerospace Engineering Autonomous Vehicle Laboratory and Alfred Gessow Rotorcraft Center, is the smallest and most capable to date as it meets most of the challenges set forth by DARPA's nano-air-vehicle program.
The extended video goes into much more detail, prototype history, and even a demonstration of autonomous control.