Deerweed

California Broom
Acmispon glaber var. glaber
NATIVE

Description (Jepson, PlantID.net)

• Eudicotyledon
  • Eudicots are a major lineage of flowering plants; see family for general characteristics
• Pea Family (Fabaceae)
• Small deciduous shrub
• Stems
  • Slender, green, and generally erect
  • Numerous and branching, giving a bushy look
  • Woody at base
• Leaves
  • Alternate (1 leaf at each junction with stem)
  • Each leaf is compound, with 3-6 oval leaflets
• Flowers
  • Inflorescence (flower arrangement) a group of 2-7 flowers, growing from the upper leaf axils
  • Characteristic Pea family flower is bilaterally-symmetric with a banner, wings, and keel
  • Yellow color ages to orange and red once pollinated (Ritter 2018)
  • Ovary superior (above the attachment of other flower parts)
• Fruit is a pod, about 0.8 in. long, with a curved tip, with 2 seeds
• Height to 20 in.

Distribution

• Native to California
  • Commonly in chaparral, coastal sand, and coastal sage scrub
  • See Calflora for statewide observations of this plant
• Outside California, grows in Baja California, Mexico
• Grows at elevations to 5,000 ft.

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

• Wildlife
  • Provides valuable forage for deer, especially in drought years or after fire (Montalvo 2017)
  • Flowers and seeds eaten by many insects, birds, and rodents
  • Nectar collected by hummingbirds, bees, and other insects
  • Larval food source (host) for orange sulfur (Collas eurytheme), bramble green hairstreak (Callophrys perplexa viridis), and acmon blue (Plebejus acmon) butterflies
• Native people
  • Decoction of foliage used for coughs
  • Infusion of plant taken to support blood formation
  • Roots used for soap
  • Twigs used for making brushes
  • Foliage used for house thatching and construction

Name Derivation

• Acmispon (ak-MIS-pon) – presumably from the Greek acme, “point” or “edge,” referring to the hook on the end of the fruit pod
• glaber (GLAY-ber) – Latin for “hairless”
• Deerweed – deer like to strip the leaves from the stem (Heiple 2020)
• California Broom – stems, especially when leafless, resemble those of several Old World shrubs in the Pea family (e.g. French and Scotch broom) traditionally used to make brooms (Ritter 2018)

Notes

• Like almost all members of its family, deerweed fixes nitrogen; see Pea family for more details
• Drought-deciduous as well as winter-deciduous
  • Sheds leaves during the summer to conserve water
  • Plant stems are green, so deerweed can continue photosynthesis when leafless
• Pioneer species: takes advantage of newly-opened spaces following a fire or other disturbance
  • Seed pods do not split open, but lie dormant until a fire or mechanical disturbance scarifies the hard seed coat and stimulates germination (Montalvo 2017)
  • Can quickly dominate areas in years following a fire (Bryant)
  • Mature plants do not compete well with other species and in 5-10 years will be replaced by pre-fire shrubs (Bryant)
• Flowers change color with age, probably telling pollinators whether a specific flower is worth visiting for nectar. The fading oranges and reds of the aging blossom may signal, “I’m done; don’t bother.” Flowers from more than 70 plant families use color changes to direct pollinators (Weiss 1991)
• Taxonomists recently reclassified deerweed, along with other North American plants formerly in the genus Lotus (San Diego 2006)
  • DNA analysis showed that New World Lotus species were distinct from Old World species
    • Native plants at Edgewood previously in the genus Lotus are now in the genus Acmispon
    • Non-native bird’s foot trefoil (Lotus corniculatus) is the only remaining Edgewood plant in the genus Lotus
• Edgewood’s deerweed 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

At Edgewood

• Found in chaparral and open woodlands
  • Easily seen in open areas of the Ridgeview trail
  • See iNaturalist for observations of Acmispon glaber
• Flowers May – October

See General References

Specific References

Bryant, P.J. Common deerweed (California broom), Acmispon glaber. Natural History of Orange County California. School of Biological Sciences, University of California, Irvine.

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.

Heiple, P. 2020, Jan. 25. Personal communication.

Montalvo, A. M., E. C. Riordan, and J. L. Beyers. 2017. Plant profile for Acmispon glaber (Vogel) Brouillet. Native Plant Recommendations for Southern California Ecoregions. Riverside-Corona Resource Conservation District and United States Department of Agriculture, Forest Service, Pacific Southwest Research Station, Riverside, California.

Ritter, M. 2018. California Plants: A Guide to Our Iconic Flora. Pacific Street Publishing, San Luis Obispo, California.

San Diego Natural History Museum. 2006. Changes in family, genera, and species names: Fabaceae. 5th Edition Changes from the 4th Edition. Checklist of the Vascular Plants of San Diego County. San Diego County Plant Atlas.

Spears, P. 2013, Dec. Outline of angiosperm phylogeny: Orders, families, and representative genera with emphasis on Oregon native plants. Native Plant Society of Oregon.

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

Wilson, B. 2012. Lotus scoparius, Deerweed. Las Pilitas Native Plant Nursery.