1. Tonnage survey of select North American wild-harvested plants, 2004–2005;American Herbal Products Association,2007
2. The ecology and biology of Panax quinquefolium L. (Araliaceae) in Illinois;Anderson;American Midland Naturalist,1993
3. Forest Measurements;Avery,1983
4. Bates, D., Maechler, M., Bolker, B., 2011. Lme4: Linear mixed-effects models using S4 classes. R package version 0.999375-39.
5. Herb market levels after five years of boom: 1999 sales in mainstream market up only 11% in first half of 1999 after 55% increase in 1998;Blumenthal;Herbal Gram,1999