The Gleason and Cronquist Illustrated Companion is a “must-have” for anyone who needs clear, concise line drawings to help understand fine distinctions between species. Although expensive, it’s a terrific reference that will become a classic. You will use it often and you won’t regret spending the money. Caution: it’s a big volume and very heavy; don’t plan on carrying it along in the field.
Hardcover, 960 pages, 1998.