CPC Plant Profile: Triple-rib Milkvetch
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Plant Profile

Triple-rib Milkvetch (Astragalus tricarinatus)

Astragalus tricarinatus close up of fruit Photo Credit: Michael Honer
  • Global Rank: G2 - Imperiled
  • Legal Status: Federally Endangered
  • Family: Fabaceae
  • State: CA
  • Nature Serve ID: 157476
  • Date Inducted in National Collection: 09/18/2021

Triple-ribbed milk-vetch is named for its unusual three-ribbed fruits. It is a tuffed perennial (or annual) reaching up to 50 cm in height with distinctly bicolored leaflets, the lower surfaces green and the upper surfaces white hairy. Flowers are light yellow and are produced from February to mid April. The legumes are triangular in cross-section like its presumed closest relative, the Morongo milk-vetch, Astragalus bernardinus (Spellenberg 1993; CVAG 2007)

Participating Institutions
Center for Plant Conservation
  • 08/17/2021

Duncan S. Bell and Naomi S. Fraga of California Botanic Garden note in 2021 that newly-documented populations of Astragalus tricarinatus in the Santa Rosa mountains are growing in carbonate soils, a substrate which the species had yet to be documented growing with.

The paper outlining these findings as well as summarizing other findings from recent botanical surveys can be found at the following link: Newly discovered populations of Astragalus tricarinatus (triple-ribbed milkvetch, Fabaceae) are found on carbonate soils in the Santa Rosa Mountains, Riverside County, California

Center for Plant Conservation
  • 08/17/2021
  • Demographic Research

A 2018 study by James G. C. Heintz, Lynn C. Sweet, and Cameron W. Barrows of UC Riverside found that increases in invasive species cover were associated with a decrease in the production of reproductive structures of Astragalus tricarinatus. The study also documented plant size and microhabitat characteristics in existing plots of A. tricarinatus, as well as documented new occurrences of the species. 

The paper can be found here: Microhabitat Characteristics and Impacts Of Invasive Species for The Triple-Ribbed Milkvetch (Astragalus tricarinatus [Fabaceae]) in the San Bernardino Mountains, California

  • 09/01/2020
  • Orthodox Seed Banking

Based on an September 2020 extract of the California Plant Rescue Database, California Botanic Garden holds 13 accessions of Astragalus tricarinatus in orthodox seed collection. There are as many as 48964 seeds of this species in their collection - although some may have been used for curation testing or sent to back up.

  • 08/27/2020
  • Reproductive Research

Little is known regarding the reproductive biology and ecology of Astragalus tricarinatus. Like many desert species, variable rainfall results in highly variable population sizes from year to year.

  • 08/27/2020
  • Orthodox Seed Banking

Supplement the single seed bank collection currently housed at RSABG

  • 08/05/2020
  • Seed Collection

Based on an August 2020 extract of the California Plant Rescue Database, California Botanic Garden has collected 10 seed accessions of Astragalus tricarinatus from 5 plant occurrences listed in the California Natural Diversity Database. These collections together emcompass 158 maternal plants

Nature Serve Biotics
  • 05/02/2017

Astragalus tricarinatus is known from about 37 extant occurrences. Recent field work has increased the number of known sites. Threats include grazing and trampling by livestock and roads.

Linda Prince
  • 01/01/2010

military exercises, recreational activities, off-road vehicles cattle grazing, competition with alien plants, urbanization, stochastic extinction, maintenance activities for the crude oil pipeline which runs through is habitat at Big Morongo Canyon

Linda Prince
  • 01/01/2010

The species is known from 13 occurrences totaling fewer than 500 plants (CDFG 2007), but highly variable from year to year.

Linda Prince
  • 01/01/2010

Little is known regarding the biology and ecology of Astragalus tricarinatus.

Linda Prince
  • 01/01/2010

Most of the known locations, 85%, occur on existing conservation lands in protected status, including land owned by Bureau of Land Management (Mission Creek, Big Morongo Canyon, and Whitewater Canyon), or the Wildlands Conservancy (Mission Creek). Since it is unclear how much this species relies on washes versus upslope regions, special consideration should be given to retaining an intact hydrological regime (CVAG 2007).

Linda Prince
  • 01/01/2010

Seed longevity and general reproductive biology Surveys of the slopes above the washes where this species is usually found to better describe habitat preferences, and to delimit extent and size of the populations.

Linda Prince
  • 01/01/2010

Supplement the single seed bank collection currently housed at RSABG


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Taxon Astragalus tricarinatus
Authority Gray
Family Fabaceae
CPC Number 7003
ITIS 25708
Common Names Triple-rib Milk-vetch | Triple-ribbed milk-vetch | triplerib milkvetch | triple-ribbed milkvetch
Associated Scientific Names Astragalus tricarinatus | Hamosa tricarinata
Distribution The northwest corner of the Coachella Valley in Riverside and San Bernardino counties, California includes all known populations of triple-ribbed milk-vetch. Most (11) occurrences are within a 14 x 1
State Rank
State State Rank
California S2

Joshua tree woodland and Sonoran desert scrub communities are the most common areas in which triple-ribbed milk-vetch can be found. Plants are restricted to arid, sandy or gravelly (decomposed granite) canyons. Although most populations of triple-ribbed milk-vetch are found at ~450-700 m elevation along washes, the number of individuals per population is almost always very small (less than 10 plants), thus A. Sanders (unpublished) believes larger populations probably occur upslope. This hypothesis was born out by the recent discovery of a large (300 individuals) population in 2004 (White 2004, 2005) at ~1200 m elevation.

Ecological Relationships

Little is known of the reproductive biology of this species. Like many desert species, variable rainfall results in highly variable population sizes from year to year. Associated species vary considerably depending on substrate, but may include Larrea tridentata, Acacia greggii, and Salix sp., or Pinus monophylla, Arctostaphylos glauca, and Populus fremontii.

Common Name Name in Text Association Type Source InteractionID

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