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 them: 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.