Dense-flowered lupine (Lupinus densiflorus) COSEWIC assessment and status report: chapter 5

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Species Information

• Name and Classification
• Morphological Description
• Genetic Description

Name and Classification

Scientific name:

Lupinus densiflorus Benth.
Synonymy (from Pojar 1999; U.S.D.A. Natural Resources Conservation Service Plants Database):
Lupinus densiflorus Benth. var. scopulorum C.P. Smith
Lupinus microcarpus Sims var. scopulorum C.P. Smith
Lupinus densiflorus Benth. var. latilabris C.P. Smith
Lupinus densiflorus Benth. var. stenopetalus C.P. Smith
Lupinus densiflorus Benth. var. tracyi C.P. Smith
Lupinus microcarpus Sims ssp. scopulorum (C.P. Sm.) C.P. Smith
Lupinus microcarpus Sims var. densiflorus (Benth.) Jepson

Common name:

Dense-flowered lupine or whitewhorl lupine

Family:

Fabaceae (Pea Family)

Major plant group:

Dicot flowering plant

Hitchcock et al. (1961), treating lupines in the Pacific Northwest, observed that "taxonomically, the genus is probably in a more chaotic state than any other to be found in our area". They noted that the species are extremely plastic and that many species interbreed freely. Barneby (1989) mentions the morphological uniformity of flowers and pods, which complicates classification. There is no evidence of Lupinus densiflorus breeding with other species in the Pacific Northwest.

Lupinus densiflorus, a member of the informal group Microcarpi, has a complicated history. Bentham described the combination but many taxonomists have included it within L. microcarpus, an earlier combination described from material grown in England from seed likely collected in Chile. Dunn and Gillett (1966) concluded that the two species --L. densiflorus and L. microcarpus --are distinct based on a number of morphological attributes. Riggins (1988) disagreed on the basis of a multivariate analysis of morphological characters and placed all members of the Microcarpi within one L. microcarpus.

Smith (1917, 1918a,b,1919) described five species and 35 new or newly combined varieties within the Microcarpi,but subsequent authors have been reluctant to recognize all of Smith’s taxa. Recent authors have referred to the element occurring in the Victoria area as L. densiflorus var. densiflorus (Pojar 1999), L. densiflorus var. scopulorum (Douglas et al. 1990), L. microcarpus var. scopulorum (Hitchcock et al. 1961) and L. microcarpusvar. microcarpus (Riggins and Sholars 1993).

Pojar (1999) recognized B.C. material as L. densiflorus var. densiflorus and his taxonomy has been adopted in this report. Apart from the three populations of Lupinus densiflorus var. densiflorus treated in this report there are no other Canadian occurrences of Lupinus densiflorus or L. microcarpus. The Canadian element of this species is referred to simply as Lupinus densiflorusin this report.

Morphological Description

Lupinus densiflorusis an annual taprooted species that is usually branched and grows to 20-30 cm in height (Figure 1). The stems are usually fistulose (hollow and cylindrical) at the base, and sparsely to copiously long, brownish-pilose (long soft straight hairs). The leaves are palmately compound and occur basally and alternate along the stem but tend to cluster near the top. There are 8-10 elliptic-oblanceolate leaflets, 1.5-3 cm long, that are glabrous above and spreading-pilose below. The petioles are also very hairy and several times longer than the leaf blades. The stalked terminal raceme can be shorter or longer than the leaves, and may be densely clustered or interrupted, with the white to pale yellowish-white flowers in whorls. The flower clusters often persist as dried membranes when the plant is in fruit. The banner is 12-14 mm long, oblong, reflexed, short hairy on the central groove, and the wings and keel are ciliate on the margins toward the base. The calyx is bilabiate, with the upper lip membranous, very short (2-4 mm long) and 2-lobed; and the lower lip greenish, much longer (10-11 mm) and 3-toothed. The fruit is an ovate to rhomboid, hirsute (pubescent with coarse stiff hair) pod that is 1.5-2 cm long with a persistent style. The seeds, generally two but occasionally one per pod, are brownish tan to olive-coloured and 4-6 mm long.

Figure 1: Illustration of Lupinus densiflorus

Plant growth form (left); flower (top right; fruiting capsule (bottom right). Illustrated by Ronald With (Taylor, 1974).

Genetic Description

No genetic work has been completed on this species though there are attempts underway to ascertain whether there is a genetic foundation to separate the southern main distribution of this species from the disjunct northern populations of British Columbia and Washington State.