Phipps, J. B.; Robertson, K. R.; Smith, P. G.; Rohrer, J. R. (1990), "A checklist of the subfamily Maloideae (Rosaceae)", Canadian Journal of Botany, 68 (10): 2209–2269, Bibcode:1990CaJB...68.2209P, doi:10.1139/b90-288
Phipps, J. B. (2015), "Crataegus", in L. Brouillet; K. Gandhi; C. L. Howard; H. Jeude; R. W. Kiger; J. B. Phipps; A. C. Pryor; H. H. Schmidt; J. L. Strother; J. L. Zarucchi (eds.), Flora of North America North of Mexico, vol. 9: Magnoliophyta: Picramniaceae to Rosaceae, New York; Oxford: Oxford University Press, pp. 491–643, ISBN978-0-19-534029-7 p. 491
"Black hawthorn (Crataegus douglasii)". Ministry of Forests, Lands, Natural Resource Operations and Rural Development, Government of British Columbia. 2019. Retrieved 12 April 2019.
Phipps, J. B.; Robertson, K. R.; Smith, P. G.; Rohrer, J. R. (1990), "A checklist of the subfamily Maloideae (Rosaceae)", Canadian Journal of Botany, 68 (10): 2209–2269, Bibcode:1990CaJB...68.2209P, doi:10.1139/b90-288