5 literature references for Opuntia engelmannii Salm-Dyck:

Author:
Year: 1996
Title:
Source: database, NODC Taxonomic Code
Author:
Year: 2013
Title:
Source: The International Plant Names Index, botanical information system from the Royal Botanic Gardens, Kew, the Harvard University Herbaria, and the Australian National Herbarium, available at http://www.ipni.org/index.html
Author:
Year: 2000
Title:
Source: database, The PLANTS Database
Author:
Year: 1996
Title:
Source: database, The PLANTS Database
Author:
Year: 2013
Title:
Source: Tropicos, botanical information system at the Missouri Botanical Garden, available at http://www.tropicos.org/