Collared Lupine

Lupinus truncatus

close up of dark and light purple flowers
Rios trailhead | April 2011

Collared lupine (Lupinus truncatus) is a native spring-flowering plant that is found in scattered open areas in the Reserve, usually in small groups or as single plants. The pea-shaped flowers are purple, becoming magenta when fertilized. Collared lupine is easily identified by the sparsely flowered stalks and by the narrow leaflets that usually appear truncated at the ends.

Like other members of the pea family, the flower structure of collared lupine selects for a certain size range of pollinators. A pollinator must be heavy enough to depress the lower petals and expose the flower throat. This allows it access to nectar and pollen, at the same time lifting the stamens to deposit pollen on the insect’s underside.

Other Common Names:

collar lupine, collared annual lupine, blunt leaved lupine, truncate leaf lupine, wood lupine, slender lupine

Description 2,4,11,34,59

Collared lupine is a rather delicate annual lupine, usually less than two feet (60 cm) high. The plant is lightly covered with small, straight inconspicuous hairs.  It is sparsely branched, often with one main central stem. Lateral branches tend upward. The larger leaves are about three inches (7.5 cm) in estimated diameter, on petioles the same length or longer; leaves are palmately compound with five to seven linear leaflets less than 1 5/8 inch (4 cm) long. Leaflets are often bluntly cut at the ends.

Flowers are widely spaced along terminal stems. There are five sepals and five petals. Sepals are fused into two unequal lips, the upper with two lobes, the lower usually three. Flowers are “papilionaceous” (shaped like a pea flower): bilaterally symmetrical with one large petal, the banner, held upright, two lateral petals, the wings, directed forward and enclosing two smaller petals which together form the keel that, in turn, encloses the pistil and stamens.  The banner is heart shaped or oval, purple on the edges, often shading to white at the lower center; around or within the pale area are red-purple dots. The two wings are strong to pale purple; the keel, which is rarely visible, shades from whitish to strong purple.  The petals of older flowers become reddish. There are ten stamens united in a column around the pistil. The pistil consists of a superior ovary, a long curving style and a small capitate stigma. Flowers occur March through May.1

The fruit is a one chambered pod covered with short soft hairs, in shape resembling a pea pod. The dried style persists on the developing fruit. There are up to ten seeds along one side of the pod. When ripe, the two sides of the dry pod split open, often spiraling, and release the seeds.

3 petaled flower on branch

Rios trailhead | March 2017

7 leafed plant close up

Rios trailhead | April 2011

bean pod like stems on plant

Developing seed pods | Santa Inez trailhead | April 2015

Distribution 7,59,89

Collared lupine is native to southern California and northern Baja California, where it grows along the coastal strip below 4000 feet (1200 m) in sage scrub, chaparral, grasslands and disturbed areas.

Its occurrence in the Reserve is somewhat unpredictable. Some years there are few plants. Other years, such as the spring of 2017 after a rainy winter, plants are scattered along the main south side trails in both Central and East Basin. We have never seen collared lupine in dense displays.

Classification 2,11,44,59,143

Collared lupine is a dicot angiosperm in the pea family (Fabaceae, formerly Leguminosae), the third largest family of flowering plants in the world. Members of the pea family are characterized by their distinctive flower (papilionaceous) in which five petals are arranged into a bilateral arrangement of one banner, two wings and a keel. Fruit is a one-chambered pod that has the seeds anchored along one side and that splits open on maturity. Leaves are often compound. Members of the pea family often harbor nitrogen-fixing bacteria in special root nodules.

The pea family is one of the most economically important families 44 and contains many well-known plants including garden flowers such as sweet pea, wisteria and acacia, and vegetables such as  beans, peanuts and soybeans. In agriculture, plants are used for forage (e.g. alfalfa)  and as cover crops to restore nitrogen-depleted soils (e.g. field peas and clovers 41). Some members of the pea family are toxic (e.g.locoweed and lupine 209). “It is possible to poison yourself with members of this family, but it takes some effort.”143

Twenty-seven members of the pea family have been reported in the Reserve, many of them non-native species. Common native relatives include ocean locoweed (Astragalus trichopodus), deerweed (Acmispon glaber) and chaparral sweet pea (Lathyruslatiflorus).

Jepson eFlora Taxon Page
purple colored flower

Intact flower | Santa Inez trailhead | April 2017

microscopic view of purple flower open with red tipped petal

Wing petal removed to expose keel | Santa Inez trailhead | April 2017

close up of purple colored flower with pollen inside

Wing and keel petals removed to expose stamens and pistil | Santa Inez trailhead | April 2017

Ecology 59

The unique shape of the classic pea flower, including that of collared lupine, is thought to be an adaptation to select for pollinators of a certain size. The reproductive organs are enclosed within the keel petals which in turn are enclosed by the wing petals. They are not readily accessible to pollinators. If a pollinator (a bee for instance) of sufficient weight lands on the platform formed by the wings, the wings and the keel are depressed, exposing the throat of the flower and forcing the stamens and pistils upward against the bee’s underparts, either depositing pollen onto the bee from ripe anthers or receiving pollen from the bee onto the pistil. In collared lupine, this mechanism selects for larger pollinators over smaller. The anthers mature before the pistil is ripe, reducing the chance of self-pollination. After fertilization, the flower becomes a red-purple. As with deerweed (Acmispon glaber), this is thought to signal pollinators that it has stopped producing nectar and pollen; the insect should go elsewhere.

purple flowers growing off the sides of a stem

Santa Helena trailhead | April 2010

field with purple flowers showing through

Rios trailhead | March 2017

green plant stem with flowers beginning to blossom

Santa Inez trailhead | April 2017

Human Uses

Many uses have been reported for several of the lupine species; many were for ceremonial and medicinal purposes, a relatively few for food.282 As a group, lupines are classified as highly toxic,209 although the roots and seeds of some species may be edible after cooking.310 Reports of the Chumash preparing seeds for food have been questioned because of a possible translation mixup between lupine and wild cherry (Prunus ilicifolia).15 The Luisaño are said to have eaten the stems and leaves of collared lupine, but there is no information about cooking.17 We have found no reports of lupine use by the Kumeyaay.16,219,272

dried out flower petals curled up on stem

Seed pods that have spiralled open | Santa Helena trailhead | May 2016

purple flowers growing off side of plant stem

Rios trailhead | March 2017

bushes with purple flowers within

Rios trailhead | April 2017

Interesting Facts 21,59

The genus name, Lupinus, appears to be derived from the Latin word “lupus” or “lupinus”, which means wolf. According to botanical lore, lupines were once thought to rob the soil of nutrients the way a wolf robs the chicken coop – an odd etymology given the soil enriching characteristics of the genus.

dark and light purple growing off stem

Santa Helena trailhead | April 2009

collection of plants with purple flowers on them

Photo credit: Paul Worthington | Rios trailhead | April 2017

purple flowers hanging off sides of stem

Photo credit: Barbara Wallach | April 2010

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