Every field botanist has a vital array of reference books and field guides addressing the composition and distribution of the flora of their region of interest. Botanists interested in the flora of Pennsylvania now have an important new resource. The Vascular Flora of Pennsylvania: Annotated Checklist and Atlas is the most detailed, comprehensive and up-to-date reference on the distribution of the ferns, fern allies, conifers and flowering plants known to occur in the Commonwealth. Greatly expanding on a previous work by Edgar T. Wherry, John M. Fogg, Jr. and Herbert A. Wahl published in 1979, the Atlas covers over 3,000 native and non-native vascular plant species.