Publication: Sp. Pl. 2: 1012.
selected vouchers: WTU
Notes: Not in H&C; listed as noxious by state of WA. Curtis Bjork has confirmed that it is not only present, but is becoming quite a pest: "It's killing Crataegus all over the Palouse and has been agressively spreading for decades. In some places it grows so robustly, it resembles pictures those monster nonnative vines in the SE states, like kudzu and Lonicera japonica."