I notice that when I add leaves to my paintings they don't look as convincing as the flowers they support.
I am convinced it's because we don't know what leaves look like.
Consider geranium leaves. All leaves are not solid green. Maybe it is over -watered and yellow in places, or is too dry and has some red or crispy spots.
With plants bursting all around us, gather some up and teach your brain with memories of leaves. (1) Make leaf rubbings with pencil and tracing paper. Then (2) with the rubbing face-down, use a ballpoint to trace the leaf into a journal or on watercolor paper, and (3) paint what you see.
In this picture, I have geranium, vinca, and boxwood leaves. I am amazed to see that the dried boxwood leaves "shimmer like gold." Lovely!
Try it and let us all know what you think about the experience.