Landscaping With Native Plants, 08 Jun 2017 https://link.springer.com/chapter/10.1007%2F978-94-017-9852-5_6#page-2
North American Butterfly Association (NABA), 08 Jun 2017 https://link.springer.com/chapter/10.1007%2F978-94-017-9852-5_6#page-2