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Yavapai County Native & Naturalized Plants

Astragalus wootonii - halfmoon milkvetch

Synonyms: Astragalus allochrous, Astragalus wootonii
Other Common Names: Wooton loco, halfmoon milkvetch, rattleweed, locoweed
Plant Form: Forb or Subshrub

Family: Fabaceae

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Patrick Alexander @
Patrick Alexander @
Patrick Alexander @
Forb Plant Description

Origin: Native   Life Cycle: Biennial or annual
General Desc: Herbage covered with short stiff hairs along the stem; several or many flower clusters; pods long and enlarged. When dry, the seeds in the pod break loose and rattle, giving it the name rattleweed.
Identification notes: Ascending to trailing annual or biennial; leaves are compound with narrow leaflets (1/8 inch wide) that are hairy on the underside; flowers are bright to light purple, <1/2 inch long; fruits are 1-celled greatly inflated pods.
Height: 3 to 12 inches


Habitat Description: Found on grasslands, chaparral, woodlands and riparian areas.
Plant Communities: Interior Chaparral, Semidesert Grasslands, Pinyon Juniper Woodland, Riparian
Elevation: 3000 - 7100 feet

Flower Characteristics

Color: Bright to light purple     Shape: Other in elongated clusters     Tubular: Y     Flowering Period: Mar - Jul
Description: Flowers less than 3/8 inch long; keel (two lower) petals arched; flower clusters of 5 to 10 flowers; sepals 2/3 as long or longer than the flower petals.

Leaf and Stem Characteristics

Leaf Color: Green     Leaf Type: Compound     Leaf Shape: Narrow     Leaf Margin: Smooth     Leaf Attachment: Alternate     Leaves Clasp: N
Hairs: Leaves     Spines: N
Leaf Description: Leaves 1-1/2 to 4 inches long with 11 to 23 narrow to oblong leaflets, 1/5 to 1 inch long.

Fruit and Seed Characteristics

Fruit Color: Reddish-brown   
Fruit Type: Pod
Fruit Notes: Greatly inflated pods, thin-walled, 3/5 to 1 inch long, broadly ovate and very asymmetric, much more strongly curved on the lower (dorsal) side than on the upper (ventral) side.

  Arizona Cooperative Extension
Yavapai County
840 Rodeo Dr #C
Prescott, AZ 86305
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Version 8.0  
Last Updated: Nov 21, 2021
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