Lammers (Morin) 2006 - Lammers TG (2006) Validation of Names at Subspecific Rank in North American Campanulaceae. Novon: A Journal for Botanical Nomenclature 16(1): 69-73. doi: 10.3417/1055-3177(2006)16[69:VONASR]2.0.CO;2.