Remember to get alot of blank paper, get some graph paper (the kind with a grid on it) and put it under the blank paper, and then grab a mechanical pencil, some extra graphite, a high qulaity eraser, a ruler, a compass (the kind for drawing circles, not the kind that tells you which way is north), and that one tool that mathmeticians use that I forgot the name of. You know, the one that is shaped like a half-circle and shows you angles (-90o 90o)?
Just do what Minecraft does with plants: Two intersecting planes with a Tree Texture on them. If you want to give them a general 3D shape, then maybe it will still support bump mapping.