O.A.Popova Rhamnus prinoides L'Hér. – shiny-leaf buckthorn Rhamnus procumbens Edgew. Rhamnus prunifolia Sm. Rhamnus pulogensis Merr. Rhamnus pumila Turra Rhamnus punctata Boiss. Rhamnus purandharensis Bhandari & Bhansali Rhamnus purpurea Edgew. Rhamnus pyrella O.Schwarz Rhamnus qianweiensis Z.Y.Zhu Rhamnus rahiminejadii Alijanpoor & Assadi Rhamnus rhodopea Velen. Rhamnus rosei M.C.Johnst. & L.A.Johnst. Rhamnus rosthornii E.Pritz. Rhamnus rugulosa Hemsl. Rhamnus sargentiana C.K.Schneid. Rhamnus saxatilis Jacq. – rock Buckthorn, Avignon buckthorn, Avignon berry, dyer's buckthorn (syn. R. infectoria, R. infectorius) Rhamnus schlechteri Lauterb. Rhamnus seravschanica (Kom.) Kamelin Rhamnus serpyllacea Greuter & Burdet Rhamnus serrata Humb. & Bonpl. ex Schult. – sawleaf buckthorn Rhamnus sibthorpiana Schult. Rhamnus smithii Greene – Smith's buckthorn Rhamnus songorica Gontsch. Rhamnus spathulifolia Fisch. & C.A.Mey. Rhamnus staddo A.Rich. – (syn. R. rhodesicus) Rhamnus standleyana C.B.Wolf Rhamnus subapetala Merr. Rhamnus sumatrensis Ridl. Rhamnus sumbawana Lauterb. Rhamnus tangutica J.J.Vassil. Rhamnus taquetii (H.Lév. & Vaniot) H.Lév. – Jejudo buckthorn Rhamnus thymifolia Bornm. Rhamnus tonkinensis Pit. Rhamnus tortuosa Sommier & Levier Rhamnus triquetra (Wall.) Brandis Rhamnus tzekweiensis Y.L.Chen & P.K.Chou Rhamnus utilis Decne. – Chinese buckthorn Rhamnus velutina Boiss. Rhamnus virgata Roxb. Rhamnus wightii Wight & Arn. – Wight's buckthorn Rhamnus wilsonii C.K.Schneid. Rhamnus × woloszczakii Kárpáti Rhamnus wumingensis Y.L.Chen & P.K.Chou Rhamnus xizangensis Y.L.Chen & P.K.Chou Rhamnus yoshinoi Makino Distribution Rhamnus has a nearly cosmopolitan distribution, with about 140 species which are native from temperate to tropical regions, the majority of species are from east Asia and North America, with a few species in Europe and Africa. North American species include Rhamnus alnifolia, alder-leaf buckthorn, occurring across the continent, and Rhamnus crocea, hollyleaf buckthorn, in the west. Though not native to this region, Rhamnus cathartica can be found in North America. Buckthorns may be confused with dogwoods, which share the curved leaf venation; indeed, "dogwood" is a local name for R. prinoides in southern Africa. The two plants are easy to distinguish by slowly pulling a leaf apart; dogwoods will exude thin, white latex strings, while buckthorns will not. Invasive species Rhamnus cathartica, the common buckthorn, is considered an invasive species in the United States and by many local jurisdictions and state governments, including Minnesota and Wisconsin. The common buckthorn is well-adapted to spreading in Canada and the U.S. It is an efficient grower that does not need much sunlight and or fertile soil. Its seeds are hardy, as well as being able to grow and spread easily in a variety of environmental conditions.