To me the difference is in the way they use their strength...
The Green Man is the vital force the natural instinct ...we can't help our selves it is just such a forceful feeling....we have to burst forth and accomplish....whatever.
It is like the vital force that causes a little seed in the ground to fight it's way to the light and burst out of it's casing.
Or a vine to grow and grow and grow all the way to the top of a telephone pole...nothing can stop it's vigor.
The Green Woman is that gentle vigor that causes a flower petal warmed by the sun to slowly open.
She understands the need for water, light, warmth...all the care giving aspects the plants need.
Her joy is in the color, fragrance and beauty of things.
She brings things to fruition using gentle strength...kind of like the Strength card in the tarot deck.
Where I see the Green Man more as the Emperor in the tarot deck...
He's the force....have you ever seen a little plant that has grow right up through a concrete side walk...he is that force...life that bursts forth no matter what obstacle.
So the GM is the force that causes the seed/plant to grow ....the GW is the enviroment...that causes it to florish and complete it's life cycle.
Anyway that's how I've come to see them.