Dense-flowered lupine (Lupinus densiflorus) COSEWIC assessment and status report: chapter 6

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Distribution

• Global Range
• Canadian Range

Global Range

Lupinus densiflorus (sensu lato) ranges from Vancouver Island and coastal Puget Sound, south on the east side of the Cascades to Baja California (Hitchcock and Cronquist 1973; Figure 2). The variety scopulorum (a more narrowly defined taxon that includes all Canadian material) is restricted to the area of Victoria, British Columbia,and adjacent islands of Washington State (Hitchcock et al. 1961, Pojar 1999).

Riggins (pers. comm.) has hypothesized that South American elements of the Microcarpi are deliberate or accidental introductions from California, made by early Spanish explorers. It is unlikely this was the case with populations in the Victoria area --Spanish explorers did not settle the area and the historical and extant populations do not correlate well with likely historical landing spots or ballast piles.

Dunn and Gillett (1966) speculated that the British Columbia populations of L. densiflorus “could represent an introduction of a seed from a single source”. They based this hypothesis on three rather weak lines of evidence: (1) the uniformity of Canadian material; (2) obligate self-pollination of the plants; and (3) the disjunction between British Columbia plants and “the main population in the southern half of California”. Subsequent authors (Taylor 1974, Clark 1976 but not Hitchcock et al. 1961 or Pojar 1999) appear to have adopted, as fact, the speculation that B.C. populations were introduced by Europeans.

The balance of evidence does not support Dunn and Gillett’s hypothesis. Morphological and even genetic uniformity among annuals is not unusual, particularly in the genus Lupinus. Additionally, a single seed source certainly does not imply an anthropogenic introduction. Finally, the disjunct distribution of “var. scopulorum” (=var. densiflorus in Canada) is paralleled by several other “semi-desert”species^Footnote 1 of the Pacific Northwest (Hitchcock et al. 1961), and it is unreasonable to assume they are all introductions. The sub-Mediterranean climate of Victoria and the Georgia basin is anomalous along the Pacific Northwest coast and may account for the pattern of disjunct distributions observed by Hitchcock et al. (1961).

Figure 2: North American Distribution of Lupinus densiflorus

Distribution in Mexico not shown.

Three other lines of evidence support recognition of var. densiflorus as a native endemic to the area. Firstly, it is locally abundant and well distributed in the San Juan Islands of the Georgia basin despite the poor dispersal abilities of its seeds. Secondly, local material appears to be distinct (hence its recognition by some as var. scopulorum). Thirdly, it was collected in Victoria in 1887, early in the European settlement of Vancouver Island and at the very beginning of botanical studies in the area. In conclusion, there is little evidence to suggest it is an introduced taxon.

Canadian Range

In Canada, L. densiflorus is restricted to three populations in the Victoria area of British Columbia (Pojar1999; B.C. Conservation Data Centre database 2002; Figure 3). The extent of occurrence is a triangle demarcated by these three occurrences and measuring approximately 2 km². The area of occupancy measures about 0.12 ha (0.0012 km²).

Figure 3: Canadian Distribution of Lupinus densiflorus

Lupinus densiflorus was formerly known from Clover Point, Victoria, where it was last collected on beach slopes and “grasslands”(RBCM accession numbers 101329 and 100762) in 1954. A 2001 survey of Clover Point failed to find any extant populations. This likely represents a historic decline in number of populations, number of mature individuals, and area of occupancy but no change in the extent of occurrence.