San Joaquin Milkvetch

astragalus asymmetricus

The San Joaquin Milkvetch is an eye-catching, robust perennial herb native exclusively to California's Central Valley and the surrounding foothills. Belonging to the diverse Fabaceae (pea) family, this plant is known for its tall, leafy, erect stems and striking clusters of cream-colored flowers. It plays a unique role in its dry, grassy ecosystems, adapted to thrive under the intense summer heat of California's interior valley. While it looks delicate, it is a tough survivor with a chemically complex makeup. Historically, members of the Astragalus genus are notorious for their chemical defenses, earning some species the name 'locoweed' due to their toxic effects on grazing livestock. For nature enthusiasts exploring California's oak woodlands and open grasslands, spotting this endemic milkvetch is a treat, especially when its highly unusual, asymmetric seed pods swing in the breeze.

Habitat: Typically found in the dry grasslands, oak woodlands, and open scrublands of California's Central Valley and Coast Ranges, often thriving in clay or sandy-loam soils.

Appearance

This erect perennial herb stands between 50 to 120 centimeters tall, supported by thick, hollow, pale green stems covered in fine, clean hairs. Its leaves are divided into numerous small, oval leaflets arranged in pairs along a central stalk. During spring, it produces dense, showy clusters of tubular, cream-colored to pale yellow pea-like flowers. The most distinguishing feature of this plant is its seed pods: they are heavily inflated, hanging downwards on long, thin stalks, and noticeably lopsided or asymmetric in shape.

KingdomPlantaePhylumTracheophytaClassMagnoliopsidaOrderFabalesFamilyFabaceaeGenusAstragalus

San Joaquin Milkvetch

Interesting facts

Like several other Astragalus species, it is classified as a 'locoweed' because it contains swainsonine, an alkaloid toxic to the nervous systems of horses and cattle.

The papery, inflated seed pods act like tiny balloons, allowing them to float on water or roll along the ground in high winds to spread their seeds.

The species name 'asymmetricus' directly references the plant's highly unusual, lopsided seed pods that hang unevenly from their stalks.

Special abilities

It can absorb and concentrate high levels of selenium from the soil, making its tissues toxic to herbivores and deterring grazing.

Hosts symbiotic Rhizobium bacteria in its root nodules to convert atmospheric nitrogen into usable nutrients, enriching poor soils.

Produces highly inflated, lightweight, asymmetric seed pods that act as sails, catching the wind easily to disperse seeds away from the parent plant.

Measurements & details

Length: 50-120 cm
Lifespan: 3-10 years

Diet & Feeding

As an autotrophic plant, the San Joaquin Milkvetch produces its own energy via photosynthesis, converting sunlight, water, and carbon dioxide into sugars.

Primary Foods

Sunlight
Water
Carbon dioxide
Soil nutrients

Ecological connections

mutualism

Yellow-faced Bumble Bee

Bombus vosnesenskii

Provides nectar and pollen, relying on this native bee species for pollination.

eaten by

Domestic Cattle

Bos taurus

Occasionally grazes the foliage, which can lead to severe toxic neurological symptoms known as locoweed poisoning.

mutualism

Western Honey Bee

Apis mellifera

Visits the creamy blossoms during spring to forage for nectar and assist in pollination.

Traits

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Also known as

No aliases listed yet.

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Safety

Danger

1/5 · Very low

No special safety notes yet.

Frequently Asked Questions

How to identify San Joaquin Milkvetch?

The easiest way to identify San Joaquin Milkvetch is to use the Snappit nature identifier app.

How long is San Joaquin Milkvetch?

50-120 cm

How long does San Joaquin Milkvetch live?

3-10 years

What does San Joaquin Milkvetch eat?

As an autotrophic plant, the San Joaquin Milkvetch produces its own energy via photosynthesis, converting sunlight, water, and carbon dioxide into sugars.

Where is San Joaquin Milkvetch usually found?

Typically found in the dry grasslands, oak woodlands, and open scrublands of California's Central Valley and Coast Ranges, often thriving in clay or sandy-loam soils.