Answer:
The root tops the trunk on this backward thing, that grows in the winter and dies in the spring.
I march before armies, a thousand salute me. My fall can bring victory, but no one would shoot me. The wind is my lover, one-legged am I. Name me and see me at home in the sky.
Only one color, but not one size. Stuck at the bottom, yet easily flies. Present in sun, but not in rain. Doing no harm, and feeling no pain.
They try to beat me, they try in vain. And when I win, I end the pain.
A harvest sown and reaped on the same day in an unplowed field. Which increases without growing, remains whole though it is eaten within and without. Is useless and yet the staple of nations.
I’m grown from darkness but shine with a pale light. Very round I am and always a lady's delight.