The Genera of North American Plants. Band 1, Philadelphia 1818, S. 296–297, (online).
doi.org
Root Gorelick: Northern Range Limit of Opuntia fragilis and the Cactaceae is 56°N, Not 58°N. In: Madroño. Band 62, Nr. 2, 2015, S. 115–123 (doi:10.3120/0024-9637-62.2.115).
google.de
books.google.de
Supplementum Plantarum Succulentarum. J. Harding, London 1819, S. 82–83 (online).
