Diario del proyecto Cacti of Ontario

Opuntia polyacantha Haw. (Cactaceae) was previously excluded from the "Atlas of the Rare Vascular Plants of Ontario" as an unconfirmed species.

Argus, G.W., C.J. Keddy, K.M. Pryor and D.J. White. 1982-1987. Atlas of the Rare Vascular Plants of Ontario, G.W. Argus & D.J. White (eds.). National Museum of
Natural Sciences, Botany Division, Ottawa, Ont.

"Excluded species of Cactaceae / Espèces de Cactaceae exclues

J/SI - unconfirmed/situation incertaine

USI Opuntia polyacantha Haw."

https://www.biodiversitylibrary.org/item/109262#page/224/mode/1up

"Notes from Canada"

T J W Burgess
Published in Botanical Gazette, in 1882, in volume 7, issue 8/9, pages 95-96

https://biostor.org/reference/209928

" Notes from Canada. —

Having in the latter part of June,
made a collecting tour with my friends. Professor Macoun, Dominion Naturalist; Mr. Wm. Saunders, Editor of the Canadian Entomologist; and Mr. James Macoun, to Point Pelee, Essex Co., Ontario, the most southern point on the mainland in Canada, a list of the rarer plants found there might not be void of interest to some of the readers of the Gazette. The list is chiefly remarkable for the southern nature of most of the species enumerated, some of
them so much so, that I had not dreamed of finding them within our
boreal confines. To this locality never before having been thoroughly explored, may be attributed the seemingly extraordinary fact, that
or the plants mentioned, the first eleven have not, I believe, been
heretofore recorded as found in Canada, while the remaining ten
have but very rarely been noted.

Opuntia Rafinesquii, Eng."