Dense-flowered lupine (Lupinus densiflorus) COSEWIC assessment and status report: chapter 2

Species Information

Lupinus densiflorus is an annual species, 20-30 cm tall. It has palmately compound leaves that occur at the base of the plants and alternately along the stem but tend to cluster near the top. The leaf stems and undersides, stems, flowers, and stalks are densely hairy and give the plant a distinctive, easily identifiable look. The white to pale yellowish-white flowers are densely clustered in whorls and give rise to egg-shaped pods that contain one or two seeds. Only a single variety of this species is recognized in Canada (L. densiflorus var. densiflorus).

Distribution

In Canada, Lupinus densiflorus occurs in localized populations in southern British Columbia. The populations tend to be small and intermittent on eroding shoreline slopes. At the species level, L. densiflorus ranges from British Columbia south to California where the taxonomy of the species is complicated by the presence of several varieties. The British Columbia populations, together with the plants in adjacent Washington state, are sometimes placed in a more narrowly-defined taxon (L. densiflorusvar. scopulorum) that has a very restricted distribution, only extending from Victoria to adjacent islands in Puget Sound, Washington.

Habitat

In Canada, Lupinus densiflorus inhabits dry to moist grassy openings, clay cliffs and eroding grassy banks and benches above the seashore. It favours south or west facing exposures and level sites within the Coastal Douglas-fir biogeoclimatic zone. 

Biology

Lupinus densiflorusis an annual herb that flowers from May until October. Most seeds germinate in the following autumn and winter while others remain dormant on the soil surface at least until spring. Seed set begins in June and July and may be prolific;seedsare thought to be gravity dispersed, though strong onshore winter winds may be anoccasional dispersal agent. 

There is little observed seed, flower or leaf herbivory, though large portions of the cotyledons may be consumed in some individuals and sub-populations. Most mortality probably occurs during the seedling stage and chance events during this period probably dictate year-to-year population fluctuations.

Population Sizes and Trend

Of the four sites at which L. densiflorus has been collected, the populations at three sites were confirmed in 2001 with population numbers ranging from 227 to 1045 individuals. The fourth population has been extirpated. There is not enough information to determine trends within populations, particularly the seed bank component of this annual species. 

Limiting Factors and Threats

The primary threat to Lupinus densiflorus in Canada is the loss and degradation of shoreline habitat on public lands in the Victoria area due to property development and recreational use. Introduced shrubs and grasses also threaten the persistence of populations. All three populations are also at risk from oil spills since they grow near sea level along one of the most active oil shipping lanes in North America. Managing sites for this species is difficult because of the high public pressure for recreational opportunities and because there are few effective tools to control exotic shrubs and grasses.

Special Significance of the Species

The Canadian populations are a major component of a disjunct element that is often treated as a distinct variety endemic to Victoria and nearby islands of Washington State. Aboriginal use of this species has been reported in a major ethnobotany database.

Existing Protection

Lupinus densiflorusis not legally protected by provincial or federal legislation or by site management plans for areas where it occurs.