For painting the thistle, I mixed four greens, darkest to lightest. The darkest one is sap green with some ultramarine blue, paynes gray, and a little raw umber. The lightest are two greens mixed with radiant yellow and cadmium lemon yellow (to give a bright pop of color.)
I find painting the darkest color first and then moving to the next lightest allows for easy blending. And, having the darkest section in first helps create the structure of the plant.