Deerweed

Acmispon glaber

Overview

 

Overview

Much of the year, deerweed looks like a discarded bundle of sticks, but in spring, when the long slim branches are covered with small bright yellow and orange flowers, the plant is eye-catching.

Deerweed (or coastal deerweed or California broom, Acmispon glaber) is one of the first species to colonize disturbed areas, especially post-burn regions. Like many members of the pea family, the roots of deerweed contain symbiotic nitrogen-fixing bacteria, which transform atmospheric nitrogen into nitrogen compounds that can be used by higher plants. Deerweed is the most abundant coastal sage scrub plant to support nitrogen fixation, which makes it an important post-fire colonizer.

    

                                        

 

Description

Description 2,4,11,26,59

Deerweed is a shrubby perennial with wiry, green branches arising from near the base of the plant. When not crowded, the plant assumes a hemispherical shape, usually less than three feet (1 m) high.

The hairless or sparsely-haired leaves usually consist of three oval leaflets, 1/4-3/8 inch (6-15 mm) long; when more than three, leaflet arrangement is pinnate. Leaves may be shed during the dry summer.

Deerweed flowers are 1/4-3/8 inch (7-12mm) long, yellow, aging to orange. They have the bilateral shape of a typical pea flower. The upper petal is large and flares upward forming the “banner”. Two side petals (“wings”) are directed forward, enclosing or concealing the remaining two petals which are fused lengthwise into a “keel”. In turn, the keel encloses the male and female reproductive structures. Flowers are bisexual. There are ten stamens, nine united and one free, and a single pistil.4, 26 Clusters of two to seven flowers attach directly to stem at a single point, and many clusters along the stem open about the same time. The main bloom period is March-July, but some flowers may be found throughout the year.1

Fruit is a two-seeded pod 5/8 inch (1-1.5 cm) long, somewhat curved upward and tapering to a long beak. Unlike most related plants, the pod does not open to release the seeds. Seeds are important food for many birds and small animals, which may be important dispersal mechanisms.11 

 

              

 

Other Common Names: 
coastal deerweed, California broom

Distribution

Distribution 7

Deerweed is native to California and is widely distributed throughout the state below 1600 feet (5,000 m). It is also found in Arizona and Mexico. It prefers dry disturbed areas in chaparral, coastal sage scrub and coastal strand.

It is common along the trails of the Reserve, especially in open areas. Deerweed is one of the dominant plants on the newly purchased (and highly disturbed) Harbaugh Seaside Trails along Coast Highway north of Solana Beach.

          

 

This plant occurs primarily in the following vegetation types in the San Elijo Lagoon Ecological Reserve: 
Chaparral
Coastal sage scrub
Coastal strand

Classification

Classification 2,59

Deerweed is a dicot angiosperm in the pea (legume) family (Fabaceae; previously called Leguminosae).4 Members of this family are characterized by their fruit, which is an elongated pod with seeds attached along one seam and which usually opens along the opposite seam. Most members of this family have a flower similar to a pea or sweet pea flower. Many members are associated with nitrogen-fixing bacteria in root nodules.11

The pea family is the third largest family of angiosperms in the world and one of the most economically important, often associated with developing societies.44 In addition to peas and beans, the Fabaceae includes peanuts, licorice, acacia and clover. Other members of this family found commonly in the Reserve include ocean locoweed (Astragalus trichopodus), collared lupine (Lupinus truncata) and chaparral sweet pea (Lathyrus latiflorus).

There are six species of Acmispon reported from the Reserve48 including the endangered Nuttall's lotus (Acmispon prostratus). Of the six, deerweed is the most common.

There are two varieties of A. glaber, distinguished on basis of relative length of wings and keel. The variety in the Reserve is A. glaber var glaber.48

 

              

 

Alternate scientific name(s): 
Lotus scoparius

Ecology

Ecology

Although deerweed rarely survives a fire, germination of the seeds is stimulated by heat34 leading to rapid post-fire colonization.14  Deerweed often dominates the second year after a burn.26 Like many members of the pea family, the roots of deerweed contain symbiotic nitrogen-fixing bacteria that transform atmospheric nitrogen into nitrogen compounds that can be used by other plants.4,13 Thus deerweed aids soil recovery by replacing nitrogen lost during the fire.34,35 Deerweed is gradually displaced as the pre-fire vegetation recovers.34

Deerweed is drought deciduous, but the stems contain chlorophyll allowing the plant to continue to photosynthesize and grow.35

The change in flower color from yellow to orange follows pollination. Most plants drop their petals immediately, since the pollinator-attracting job of the petals is no longer needed. Nevertheless a number of unrelated species have evolved a color change, leading a colleague of Charles Darwin, Fritz Müller, to speculate that retention of the petals enhances the color presence of the plant and hence the distance from which it can be recognized by a pollinator.63 At the same time, Müller postulated that the color change directed the pollinator away from the fertilized flower, which no longer needed its services, to unfertilized flowers with ample rewards of nectar and pollen. In the intervening 200 years, ecologists have confirmed these speculations.63 Furthermore, it has been shown that insects must learn the difference between colors. Naïve insects will visit the wrong flower before learning where the nectar and pollen can be found.64

 

              

 

Human Uses

 

Human Uses 

We have found no information about deerweed use by local Native Americans (Kumeyaay or Luiseño). The Chumash to the north used the branches as a broom for rough sweeping. The smoke from deerweed was used to blacken Juncus to be woven into baskets to provide design. Deerweed was also used for thatching sweathouses.15

Deerweed is highly recommended for butterfly gardens.65

 

             

 

Interesting Facts

Interesting Facts

The common name, deerweed, appears to come from the fact that the plant is nutritious and readily eaten by deer and other grazers;27 however not all references agree on the palatability.11 The name broom derives from the shape of the plant, which resembles a broom buried handle down59 and/or to its early use as a broom.

 

            

 

Photos

Central Basin, southwest side (Pole Road); March 2009
East Basin, south side (Santa Carina trailhead); April 2010
East Basin, south side (Santa Carina trailhead); May 2009
Cental Basin, south side (Rios trailhead); Jan. 2010
East Basin, south side (Santa Carina trailhead); May 2009
Cental Basin, south side (Holmwood Canyon); May 2010
Central Basin, southwest side (Pole Road); March 2009
Central Basin, southwest side (Pole Road); March 2009
East Basin, south side (Santa Carina trailhead); April 2010
East Basin, south side (Santa Carina trailhead); May 2009
Cental Basin, south side (Rios trailhead); Feb. 2010
Cental Basin, south side (Rios trailhead); Feb. 2010
East Basin, south side (Santa Carina trailhead); April 2010
Cental Basin, south side (Rios trailhead); Jan. 2010
Cental Basin, south side (Rios trailhead); Jan. 2010
seed pods; Cental Basin, south side (Rios trailhead); Feb. 2011
chlorophyll-containing stems; East Basin, south side (Santa Carina trailhead); Oct. 2013
May 2011; photo courtesy of Barbara Wallach
May 2011; photo courtesy of Barbara Wallach
April 2010; photo courtesy of Barbara Wallach
April 2010; photo courtesy of Barbara Wallach
March 2012; photo courtesy of Barbara Wallach
April 2010; photo courtesy of Barbara Wallach
April 2011; photo courtesy of Barbara Wallach
June 2009; photo courtesy of Denise Stillinger
June 2009; photo courtesy of Denise Stillinger