I guess I have a bit of a tree fetish. I've been taking lots of photos of interesting trees and plants over the last few months. I haven't used the photos yet, but here are some studies of trees from memory.
These are based on a scary tree I saw. Thought it would be fun to add faces. I'm planning to do a painting based on them later.
Brush and cel vinyl. Mostly just color studies, but I wasn't happy with these because there's not enough interest in the leaf shapes and patterns. Everything is too even.
These are all done with paper towel sponging. I overworked and ruined the bushes, but I'm happy with how the trees came out.
Sea sponge. Overworked some areas of these and ruined them.
I'll try some more studies... like sponging with a dish rag and keep practicing until I get the result I'm after.