Silver Bush Lupine :

Silver Lupine
Lupinus albifrons var. albifrons
NATIVE

Description (Jepson, PlantID.net)

Eudicotyledon
- Eudicots are a major lineage of flowering plants; see family for general characteristics
Pea Family (Fabaceae)
Semi-deciduous perennial shrub, with a distinct woody trunk
Entire plant hairy
Leaves
- Palmately compound (separate leaflets radiating from a single point)
- Alternate (1 leaf at each junction with stem)
- Upper and lower surfaces hairy, giving a silvery appearance
Flowers
- Inflorescence (flower arrangement) is a tall spike-like raceme (unbranched stem with stalked flowers opening from the bottom up)
- Characteristic Pea family flower is bilaterally-symmetric with a banner, wings, and keel
- Violet to lavender, with a white or yellow patch at base of banner petal
- Fragrant (some people smell grape soda)
- Ovary superior (above the attachment of other flower parts)
Fruit is a hairy legume (a single-chambered seed pod that opens along 2 seams)
Height 2-16 ft.

Distribution

Native to California
- Grows in a variety of habitats, including chaparral and coastal sage scrub, and dry, open areas of foothill woodlands and conifer forests
- See Calflora for statewide observations of this plant
Outside California, extends into southern Oregon
Grows at elevations to 4,900 ft.

Uses (San Mateo County Parks prohibits removal of any natural material)

Wildlife
- Native bees seek the pollen
  - Bumblebees are the principal pollinators as they have just the right weight to open the flower to reach the pollen
- Authorities differ on the production of nectar in lupines, perhaps because nectar production may differ by species; see Ayers (2016) for a summary of the controversy
- Larval food source (host) for multiple species of blue, hairstreak, and sulphur butterflies
  - One of 3 perennial lupines required as a host plant for larvae of the federally-endangered Mission blue butterfly (Icaricia icarioides missionensis)
CAUTION – Lupines contain varying amounts of toxic alkaloids
- Bitter taste can deter herbivores
- Some species are poisonous to livestock and humans

Name Derivation

Lupinus (loo-PIE-nus) – from the Latin for “wolf,” for uncertain reasons
- Perhaps because lupine species with high alkoloid levels can, like wolves, harm livestock and humans (Kurlovich 2006)
  - Lupines with low alkoloid levels make excellent livestock feed
- Perhaps because it was mistakenly believed that lupines depleted the soil of nutrients (Merriam-Webster 2024)
  - This seems unlikely, however, as farmers since ancient times have known that lupines, as members of the Pea family, make soils more fertile by adding nitrogen (Kurlovich 2006)
- Perhaps from the tendency of some lupines to overrun ground (Jepson)
albifrons (AL-bi-frons) – from the Latin for “white-fronded,” referring to the silvered appearance caused by hairs on the leaves

Notes

Like almost all members of its family, silver bush lupine fixes nitrogen; see Pea family for more details
Narrow, hairy leaves are adapted to conserve water in hot, dry habitat
Banner spot of lupine flowers changes color as the flower ages (Stead and Reid 1990)
- This change occurs more quickly after pollination
- Even though the flower shows no sign of wilting, color change tells visiting insects to move on to another flower
- These unwilted, pollinated flowers remain to help attract pollinators from a distance
- Flowers from more than 70 plant families use color changes to direct pollinators (Weiss 1991)
Edgewood has 7 lupine species, a remarkable number for a relatively small preserve and an indication of Edgewood’s species diversity
Edgewood’s silver bush lupine is classified as a variety
- Variety indicates a population with small morphological variations, e.g. color, seen throughout the geographic range of the species; interbreeding is possible
- Subspecies indicates a geographically-separated population with distinct morphological characteristics; when not isolated, interbreeding is possible
- In practice, botanists have not consistently applied these ranks

ID Tips

Flowers and leaves of lupines are characteristically similar
At Edgewood, the silver bush lupine is the only lupine that is a perennial woody shrub
May be confused with the 6 other lupine species at Edgewood
- Miniature lupine (L. bicolor)
- Sky lupine (L. nanus)
- Fleshy lupine (L. affinis)
- Chick lupine (L. microcarpus var. densiflorus)
- Summer lupine (L. formosus var. formosus)
- Arroyo lupine (L. succulentus)

	Silver Bush Lupine	Miniature Lupine	Sky Lupine	Fleshy Lupine	Chick Lupine	Summer Lupine	Arroyo Lupine
Growth Habit	woody shrub	annual	annual	annual	annual	perennial herb	annual; can appear a perennial herb
Height	≤ 16 ft., usually 3-5 ft.	≤ 16 in.	≤ 24 in.	≤ 20 in.	≤ 31 in.	≤ 31 in.	≤ 39 in.
Hairiness	silver-hairy	hairy	hairy	hairy	sparsely to densely hairy	densely hairy	fleshy, sparsely hairy
Leaflet Tip	pointed	sharply pointed	pointed	rounded or pointed	pointed	sharply pointed	wide, blunt
Inflorescence Length	≤ 12 in.	≤ 3 in.	≤ 16 in.	≤ 8 in.	≤ 12 in., often in distinct tiers	≤ 12 in.	≤ 6 in.
Flower Color	blue-purple ⋯ banner spot white to yellow > magenta	blue ⋯ banner spot white > magenta	blue ⋯ banner spot white > magenta	blue-purple ⋯ banner spot white > magenta	white to yellow; rose to purple ⋯ no banner spot	faded blue-purple ⋯ banner spot white or none	blue-purple ⋯ banner spot white > magenta
Fruit Arrangement	encircle stem	encircle stem	encircle stem	encircle stem	cluster to 1 side	encircle stem	encircle stem
Best Trails	all trails	Ridgeview, Sunset, Edgewood	Lower Clarkia	Lower Clarkia	Native Garden, Upper Sylvan	Upper Edgewood	Upper Sylvan

At Edgewood

Found in coastal scrub and grassland edges
- Found in many areas of Edgewood, but especially prominent along the open areas of the Ridgeview trail
- See iNaturalist for observations of Lupinus albifrons
Flowers March – May

Specific References

Ayers, G. 2016, Oct. 1. The controversy over nectar production. Introduction to genus Lupinus. American Bee Journal.

California’s endangered insects: Mission blue butterfly. Essig Museum of Entomology. University of California, Berkeley.

Elpel, T.J. 2013. Pea family – Fabaceae [Illustration of pea subfamily, adapted]. Botany in a Day: The Patterns Method of Plant Identification. HOPS Press, Pony, Montana.

Kurlovich, B.S. 2006, July 17. The history of lupin domestication. Blog. Lupins.

Merriam-Webster.com Dictionary. 2024. Lupine. Merriam-Webster.

Shapiro, A.M., and T.D. Manolis. 2007. Field Guide to Butterflies of the San Francisco Bay and Sacramento Valley Regions. University of California Press, Berkeley and Los Angeles, California.

Stead, A.D., and M.S. Reid. 1990. The effect of pollination and ethylene on the colour change of the banner spot of Lupinus albifrons (Bentham) flowers. Annals of Botany 66: 655-663.

Thorp. R., P. Schroeder, and C. Ferguson. 2002. Bumble bees: Boisterous pollinators of native California flowers. Fremontia 30(3-4): 26-31.

Weiss, M. 1991, Nov. 21. Floral color changes as cues for pollinators. Nature 354: 227-229.

Young, B. 1998, Jun. A closer look at bush lupine. Edgewood Explorer.

General References

Calflora Database. 2014. Berkeley, California.

Calscape. 2018. California Native Plant Society.

Charters, M.L. 2015. California Plant Names: Latin and Greek Meanings and Derivations.

Charters, M.L. 2017. Southern California Wildflowers: Guide to the Pronunciation of Specific, Generic and Family Names.

Corelli, T. 2004. Flowering Plants of Edgewood Natural Preserve (2nd. ed.). Monocot Press, Half Moon Bay, California.

Dave’s Garden.

Elpel, T.J. 2013. Botany in a Day: The Patterns Method of Plant Identification. HOPS Press, Pony, Montana.

Flora of North America. efloras.org.

Harris, J.G., and M.W. Harris. 2013. Plant Identification Terminology: An Illustrated Glossary. Spring Lake Publishing, Spring Lake, Utah.

Keator, G. 2009. California Plant Families. University of California Press, Berkeley and Los Angeles, California.

Native American Ethnobotany DB.

Regents of the University of California. Jepson eFlora. Jepson Herbarium. University of California, Berkeley.