USDA-NRCS PLANTS Database / Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner's Sons, New York. Vol. 2: 580.
(source URL: http://plants.usda.gov/java/profile?symbol=LYHY3&photoID=lyhy2_001_avd.tif)