Lupinus rivularis

This lupine occurs in gravelly areas, usually associated with streams or riverbanks on the west side of the Cascade Mountains (Hitchcock et al. 1961). It occurs from California north through Oregon and Washington to southern British Columbia. This species hybridizes with L. arboreus, which is native in North America only to California, and non-native in Oregon, Washington and British Columbia. Genetic swamping due to hybridization is believed to be the greatest rangewide threat; it is uncertain how much "pure" L. rivularis remains, but it may be very little. Rangewide genetic studies are needed to clarify this issue. Other threats include habitat destruction, invasive invertebrates, ground maintenance and collection.

This species extends from California north through Oregon and Washington to the most southern portion of British Columbia (COSEWIC 2002).

There are five extant occurrences in British Columbia (NatureServe Network Database as of September 2016). Occurrences are not tracked in Washington, Oregon, and California.

This species hybridizes readily with Lupinus arboreus and there may be few remaining populations that are purely L. rivularis. L. arboreus is non-native but widely planted outside of a few counties in California, and this hybridization causes genetic swamping in L. rivularis throughout much of L. rivularis' range (Hickman et al. 1993, COSEWIC 2002). In addition, in western Oregon, an unidentified lupine strongly resembling L. rivularis is commonly seeded on road verges and elsewhere. This seeded plant keys close to L. rivularis, but has a somewhat different appearance than the wild-growing L. rivularis present in undisturbed sites; this seeded material may be a cultivar of L. rivularis of unknown provenance (P. Severns pers. comm. 2008) or it could be hybrid material with a low level of introgression from L. arboreus (COSEWIC 2002). This seeded plant is now very common and can become weedy (P. Severns pers. comm. 2008), raising the concern of potential additional genetic swamping of and/or competition with natural L. rivularis plants. Habitat destruction is also a substantial threat to this species. In British Columbia, suitable habitat has been signficantly reduced by dyking of river systems in the lower Fraser Valley as well as industrial development in floodplains (COSEWIC 2002). Other threats include: invasive invertebrates, ground maintenance work, herbicide spraying, and wildflower collecting by the general public (COSEWIC 2002).