Streambank lupine (Lupinus rivularis) COSEWIC assessment and status report: chapter 4

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Distribution

Global range

This species is found globally only along the Pacific coast of North America, from southern British Columbia (Canada) to northern California (Henry 1915, Scoggan 1978, Riggans and Sholars 1993, and others) (Figure 2). Scoggan (1978) indicates that Hulten considers reports of Lupinus rivularis occurring in the Aleutian Islands erroneous. Some web-based maps that show the distribution of this species further inland in California, and in areas of higher elevations, are considered erroneous, and are likely based upon other species (Sholars 2001 pers. comm.). Our examination of specimens from California would support this.

Canadian range

Populations determined to be Lupinus rivularis

In Canada, Lupinus rivularis occurs at the northern limits of its range, and is known from only six stations in southern British Columbia: one station on Vancouver Island (near Sooke), and five stations in the lower Fraser Valley: Surrey, Delta, and Port Coquitlam, one of which supports three small subpopulations (Figure 3).

The extent of occurrence of L. rivularis in Canada is approximately 70 km². This represents two disjunctive polygons--one very small, located on Vancouver Island, of less than 1 km², and one of 70 km² located in the lower Fraser Valley. Given the lack of information on this species over time, and the fact that all of the previously known populations were rediscovered this year, our only conclusion can be that the extent of occurrence is stable. Nonetheless, given the industrial development and dyking in the lower Fraser Valley, it is probable that over the past century the extent of occurrence for L. rivularis has decreased substantially.

The area of occupancy is less than 1 km². Again, the lack of temporal knowledge on the local populations of L. rivularis prevents us from making any factual statements about trends in the area of occupancy, other than to state that it appears to have been stable over the past decade. However, it is probable that the area of occupancy has declined substantially over the past century in light of the industrial developments and extensive dyking along the Fraser River.

Figure 2. Distribution of Lupinus rivularis in North America.

Planted populations

An additional three obviously or reportedly planted lupine/wildflower populations that contain some rivularis-like plants have been observed in Vancouver (2) and New Westminster (1), and there are likely others. These populations appear to be plants from popular wildflower seed packages and were growing with California poppy and other non-native species. In general, they exhibited some hybrid traits similar to L. arboreus and L. polyphyllus, and plants ranged in appearance. Some appeared very “rivularis-like” however, and may represent a seed source from California where hybrids of these species are common.

Figure 3. Distribution of Lupinus rivularis in Canada.

Previously reported stations which have been re-determined or are erroneous

1. One specimen report of the species from Richmond in the lower Fraser Valley has been redetermined as L. littoralis.
2. Previous specimen reports of L. rivularis from Bute Inlet and Knight Inlet have been re-determined. They are not L. rivularis and appear to be based on specimens of Lupinus arcticus.
3. A specimen report from the UBC herbarium database from Mt. Copley near Arrowsmith has been determined to be erroneous, a data entry error.
4. The reports of the species from Spence’s Bridge and Shawnigan by Henry (1915) have been determined not to be L. rivularis.

Hybrid populations, not apparently planted

One hybrid population was observed in Surrey that is proximal to the Fraser River, and this may be Lupinus rivularis x arboreus. However, these plants are much closer to arboreus in appearance, and should not be construed as a L. rivularis population. (A large hybrid population was also discovered on Annacis Island that appears to support hydrids between L. arboreus and L. littoralis.)

Potential sites for further investigation

We believe that habitat for L. rivularis in the lower Fraser Valley might have been more extensive prior to dyking. However, not all creek bank/floodplain sites have been dyked, and flooding still occurs in some areas (this species prefers floodplain areas proximal to waterways). It is possible that other small populations of L. rivularis will be found in pockets of suitable habitat. Also, the opportunistic use of dykes by the species in what was likely the vicinity of previous populations indicates that other populations may occur elsewhere on the dykes proximal to the coast. Dykes may also offer some opportunities for recovery of this species, although this is unknown.