1. Albrecht MA, McCarthy BC (2006) Comparative analysis of goldenseal (Hydrastis canadensis L.) population re-growth following human harvest: implications for conservation. Am Midl Nat 156(2):229–236. doi: 10.1674/0003-0031(2006)156[229:CAOGHC]2.0.CO;2
2. American Botanicals (2008) Product list. http://www.americanbotanicals.com/product_list.asp . Cited 1 September 2008
3. American Herbal Products Association (AHPA) (1999) 1997–1999 Tonnage survey results. American Herbal Products Association, Silver Spring, MD
4. American Herbal Products Association (AHPA) (2003) Tonnage survey of North American wild-harvested plants, 2000–2001. American Herbal Products Association, Silver Spring, MD
5. American Herbal Products Association (AHPA) (2006) Tonnage survey of select North American wild-harvested plants, 2002–2003. American Herbal Products Association, Silver Spring, MD