Sauers is good, there are many early American Herbals, I put this list together for Roy Upton a while ago
Monardes (later published in English as Joyfull Newes out of the Newe Found World)1574
Badianus manuscript 1552
Josselyn New England Rarities 1672
John Clayton Account of Medicinal Practices of Virginia Indians 1687
J.C. Sauer Kurzgefasstes Krauter-Buch 1762-1778
J.D. Schoepf Materia Medica Americana 1787
Manasseh Cutler An Account of Some Vegetable Productions 1785
Stearn's American Herbal 1801
Patrick Kerr Rogers An investigation of the Properties of the Liriodendron tulipifera 1802
and there are several botanical works from the 18th century that may briefly discuss medicinal uses such as Catesby.