General Description

Threecorner milkvetch (Astragalus geyeri var. triquetrus), a member of the legume (Fabaceae) family, is a rare, sand loving, annual plant endemic (local) to Clark and Lincoln Counties in southern Nevada and Mojave County in northwestern Arizona. It has small white flowers, compound leaves, small oblong leaflets with a notch at the tip, and distinct three-angled fruit.

Legal Status

Threecorner milkvetch is listed as a critically endangered species in the state of Nevada, is on the Bureau of Land Management (BLM) sensitive species list, is listed on the Nevada Natural Heritage Programs Sensitive List as imperiled, and is a covered species on two local conservation plans; the Lower Colorado Multiple Species Conservation Plan (LCR MSCP) administered by the Bureau of Reclamation, and the Clark County Multiple Species Habitat Conservation Plan (MSHCP) administered by Clark County, NV.

Taxonomy

Astragalus is a species-rich genus, with more than 2000 species in the genus currently known worldwide. Astragalus geyeri is 1 of 350 species in the genus Astragalus in North America, while variety triquetrus is 1 of 2 in the species geyeri. The plant was first described at the confluence of the muddy river and the Virgin Rivers in 1877.

Reproduction

Threecorner milkvetch is an annual plant flowering in April setting fruit 2 -3 weeks later. The mean number of fruits produced per plant at the Sandy Cove site ranged from 1-477 fruits/plant with a mean of 54 fruits/plants.

Threats

The major threat to threecorner milkvetch is from invasive annual plant species including Sahara mustard (Brassica tournefortii), Mediterranean/Arabian grass (Schismus barbatus, S. arabicus), and tumbleweed (Salsola tragus, S. paulsenii). Additional threats are from development and off-highway vehicle (OHV) use.

More Information

Additional information on this species, as well as source documentation, can be found in the species accounts located at this link (PDF). Technical Reports on this species can be found here.

Updated November 26, 2012

The northern and eastern most distributions of this species are at Sand Hollow Wash in Lincoln County and at Coon Creek in Mojave County.  Threecorner milkvetch reaches a southern extension at Sandy Cove on the north shore of the Boulder Basin within Lake Mead National Recreation Area (LMNRA) and a western extension at Dry Lake Valley in Clark County.  The highest concentration of populations is found in the Mormon Mesa area of Clark County.

Click on the map below to see the distribution range of the threecorner milkvetch using the interactive GIS map.

Threecorner milkvetch is found in areas with deep, loose sand and has a geographic distribution associated with a sedimentary deposit called the Muddy Creek Formation. This formation is widely exposed in the hills along the Overton Arm, Virgin Basin, and Boulder Basin sections of Lake Mead National Recreation Area (LMNRA) and extends northward along the Virgin River valley and westward along the Muddy River and Meadow Valley Wash. Weathered sediments from this formation provide the substrate for threecorner milkvetch.

LCR MSCP Conservation Measures

The following information is from Volume II of the 2004 LCR MSCP Final Conservation Plan. Additional information is included in the expanded conservation measures for this species. Click on the arrows to expand the table.

Research and Monitoring Activities

LCR MSCP conduct a variety of research and monitoring activities along the LCR encompassing both MSCP and non-MSCP species. For a complete list of all activities, please see the Research and Monitoring Activities web page.

The following list includes different research and monitoring activities for vegetation. Click on the link for more information.

• Habitat Monitoring
• Sticky Buckwheat and Threecorner Milkvetch Conservation
• Soil Studies

This gallery includes photos of this species. If you require larger photos, please contact our webmaster Michelle Reilly at mreilly@usbr.gov.