Natural science illustration returns reasonable results. I think most are done traditionally in some type of watercolors.

I hate to be a contrarian, but I've always hated them. IMHO, the extra-fancy-style illustrations are just that. Now that we have wildlife photography, these seem to regress and appear much worse (again, IMHO) because they are literally an illustration of reality and not a snapshot: https://www.youtube.com/watch?v=NwhVJ7cv9B4&t=36s