Utah State University owns the copyright to the illustrations in the two grass volumes of the Flora of North America north of Mexico and their derivative products, Manual of Grasses for North America and Grasses of the Intermountain Region. If interested in using any of them, please contact Mary Barkworth (email@example.com) explaining which you wish to use and how (e.g., web site, flyer, flora, scientific publication) to obtain permission for their use and the appropriate files.
In general, the cost of a license for one time use is $35 per species but it is waived under some circumstances. In addition, it must be stated that the copyright is owned by Utah State University and the illustrations are being used with permission plus the name of the illustrator(s) involved must be included. The funds generated from the license fees are provided to the Intermountain Herbarium. Currently they are being used to create a new (and better) version of the Grass Manual web site.