Buckthorn and California buckthorn

Buckthorn noun - A shrub or shrubby tree of the genus Rhamnus; fruits are source of yellow dyes or pigments.

California buckthorn and buckthorn are semantically related. In some cases you can replace phrase "California buckthorn" with "Buckthorn", this terms are similar.

California buckthorn noun - Evergreen shrub of western United States bearing small red or black fruits.

Buckthorn and California buckthorn are semantically related. You can use "Buckthorn" instead a noun phrase "California buckthorn".