CPC Plant Profile: Braunton's Milkvetch
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Plant Profile

Braunton's Milkvetch (Astragalus brauntonii)

This shot shows the plant in detail, featuring the leaves and flowers. Photo Credit: Bart O'Brien
Description
  • Global Rank: G2 - Imperiled
  • Legal Status: Federally Endangered
  • Family: Fabaceae
  • State: CA
  • Nature Serve ID: 156760
  • Date Inducted in National Collection: 03/05/1993

This is an ephemeral perennial member of the pea family that reaches a height of 15 dm with dull lilac flowers blooming March-July (Munz 1974). It typically appears following a chaparral fire or other form of mechanical disturbance and persists several years before senescing or becoming crowded out by developing vegetation (Skinner 1991). Braunton's milkvetch seeds persist in the soil bank for many years and have a seed coat that is typical of many chaparral plants and adapted to germinate after some form of disturbance which breaks seed dormancy (USFWS 1999).

Participating Institutions
Updates
  • 09/01/2020
  • Orthodox Seed Banking

Based on an September 2020 extract of the California Plant Rescue Database, California Botanic Garden holds 14 accessions of Astragalus brauntonii in orthodox seed collection. There are as many as 961453 seeds of this species in their collection - although some may have been used for curation testing or sent to back up.

  • 09/01/2020
  • Orthodox Seed Banking

Based on an September 2020 extract of the California Plant Rescue Database, Santa Barbara Botanic Garden holds 1 accessions of Astragalus brauntonii in orthodox seed collection. There are as many as 100 seeds of this species in their collection - although some may have been used for curation testing or sent to back up.

  • 08/25/2020
  • Propagation Research

Rancho Santa Ana Botanic Garden has undertaken preliminary germination and growth experiments for possible introduction efforts (Hannon pers. comm.)

  • 08/25/2020
  • Demographic Research

USFWS section 6 funding was provided for a 1998 study of the ecology and distribution of Braunton's milkvetch, in particular soil seed bank characteristics and pollination requirements (USFWS 1999).

  • 08/25/2020
  • Demographic Research

Currently, the southern California National Forests are developing suitable habitat models for this species to identify areas on National Forest System Lands that could potentially support additional occurrences of Braunton's milkvetch and to determine whether this taxon is present or absent within these areas and if present, manage populations accordingly.

  • 08/05/2020
  • Seed Collection

Based on an August 2020 extract of the California Plant Rescue Database, Santa Barbara Botanic Garden has collected 1 seed accessions of Astragalus brauntonii from 1 plant occurrences listed in the California Natural Diversity Database. These collections together emcompass 18 maternal plants

  • 08/05/2020
  • Seed Collection

Based on an August 2020 extract of the California Plant Rescue Database, California Botanic Garden has collected 6 seed accessions of Astragalus brauntonii from 2 plant occurrences listed in the California Natural Diversity Database. These collections together emcompass 6 maternal plants

Nature Serve Biotics
  • 05/02/2017

Endemic to the mountains surrounding the Los Angeles basin, California, where it is currently known from 4 general areas. Currently, fewer than 100 individual plants are known, but the species' seed bank could generate larger populations if appropriate fire events occurred. The species may be restricted to limestone, which is a rare substrate within the limits of its known distribution. A. brauntonii is threatened by urban development and habitat fragmentation, and by the resultant alteration of natural fire cycles. The fact that the plants are only visible for 2-3 years following a fire or other disturbance (which may occur only once in 20-50+ years) may make the populations especially vulnerable to destruction.

Valerie Soza
  • 01/01/2010

The major threat to this species is immediate loss of native habitat. Most of the habitat is on private lands or in the immediate vicinity of areas of expanding urban development, including construction of housing, golf courses and infrastructure. In

Valerie Soza
  • 01/01/2010

There are 16 known extant occurrences of Braunton's milkvetch, with 12 historical occurrences that have been extirpated of presumed extirpated (CNDDB 2001). Braunton's milkvetch is currently known from four general areas in Ventura, Los Angeles, and Orange counties: eastern end of Simi Hills, eastern half of the Santa Monica Mountains, southern base of the San Gabriel Mountains, and northwestern side of the Santa Ana Mountains.

Valerie Soza
  • 01/01/2010

USFWS section 6 funding was provided for a 1998 study of the ecology and distribution of Braunton's milkvetch, in particular soil seed bank characteristics and pollination requirements (USFWS 1999). In addition, Rancho Santa Ana Botanic Garden has undertaken preliminary germination and growth experiments for possible introduction efforts (Hannon pers. comm.)

Valerie Soza
  • 01/01/2010

Currently, the southern California National Forests are developing suitable habitat models for this species to identify areas on National Forest System Lands that could potentially support additional occurrences of Braunton's milkvetch and to determine whether this taxon is present or absent within these areas and if present, manage populations accordingly.

Valerie Soza
  • 01/01/2010

More surveys are needed in suitable habitat post-fire or after some other disturbance to locate additional populations of Braunton's milkvetch. Seeds remain in the soil bank for many years before germinating and therefore, other areas that have not burned in many years could potentially support additional occurrences of this plant. Fire suppression regimes need to be reevaluated in areas of suitable habitat. In the meantime, suitable habitat should be secured and then burned periodically to stimulate germination of potential seed (Skinner 1991).

Valerie Soza
  • 01/01/2010

Because Braunton's milkvetch seed remains dormant in the soil bank for many years, there is more likely to be a higher amount of genetic diversity in the seed bank than in living plant populations. Seed should be collected from newly-discovered populations and stored at established conservation seed programs. Existing populations should be monitored annually and seed should also be collected from newly-established individuals to increase the genetic diversity and gene pool for this species stored at conservation seed programs.

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Photos
Nomenclature
Taxon Astragalus brauntonii
Authority Parish
Family Fabaceae
CPC Number 374
ITIS 25443
USDA ASBR6
Common Names Braunton's milkvetch | Braunton's milk-vetch
Associated Scientific Names Astragalus brauntonii | Brachyphragma brauntonii
Distribution Braunton's milkvetch is known to occur only in the hills bordering the Los Angeles basin in southern California, from Ventura, Los Angeles, and Orange counties. Known occurrences of this species are
State Rank
State State Rank
California S2
Habitat

Braunton's milkvetch generally occurs below 2100 feet (640 m) in elevation, on south-, west-, and east-facing slopes, in open areas within chaparral. It is often found growing in disturbed areas such as burn areas, along fire roads or fuel breaks, and in areas that have been cleared by some means and where competition is low. This plant was historically found in gravelly clay soils overlaying granite sandstone, but is now found often associated with carbonate soils derived from scattered limestone lenses, or on noncarbonates at down-wash sites (Skinner 1991; USFWS 1999).

Ecological Relationships

Pollinators that have been observed on Braunton's milkvetch are mostly native megachild bees, followed by native bumble bees (USFWS 1999).

Pollinators
Common Name Name in Text Association Type Source InteractionID
Bees
Leaf-cutting bees Megachilidae Confirmed Pollinator Link
Bumble bees Bumble bees Confirmed Pollinator Link
Other
Ant Floral Visitor Link

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