.....you can find at : http://en.wikipedia.org/wiki/Samara_(fruit)
It's a plain,minimal solution for an autorotating displacement (a "self" motion...),as the seed falls in gravity.
It can be a suggestion,in the same time ,for a single-blade propeller on account of a mechanical spinning flight.
As you can see on net,there is a lot of solutions :sometimes you can fly with an one-spoke/blade "wheel".
A concise "design" can be :a free falling lever (one arm is the blade/propeller ,the opposite arm is the seed/counterweight),within an air-fulcrum,due to gravity.
You can call it a wheel,a minimal wheel or a lever...
Maybe,as in nature,we need a "minimal design" for our "dream machine"...?!
All the best! / Alex
.....as a natural suggestion of a seed fall (self-autorotation ) in gravity ,can be related to a light-aviation propeller : http://en.wikipedia.org/wiki/Single-blade_propeller
This topic it's no more than a tiny "stimulus" to think and imagine a possible gravity motor in the most simple manner...
All the best! / Alex