The best introductory book on the subject examines plant structures and the problems they present to illustrators, then discusses the artist's tools and how to use pencils, erasers, papers, brushes, watercolors, gouache, and acrylics.
Small print, largely text. Illustrations largely on side of text, few large illustrations. All Black and white for 2/3rds of the book. The last third looks more engaging with some full color photos. I have not read it, just my observations during browsing.