Astragalus whitneyi A. Gray
Balloon-pod Milk-vetch, Balloon Milk-vetch, Whitney's Locoweed
When I was a kid I read a science fiction story about a crew of astronauts, landing on another planet. I don’t remember the details, but they noticed balloons floating in the air, and, upon examination, found they were seedpods, lofted by hydrogen gas made by the host plants. What a clever idea! It never occurred to me that something very similar exists right here on earth. The “balloons” of balloon-pod milkvetch dry out and detach, becoming brittle, and light enough to be blown hither and yon. They collide with rocks and shatter, releasing their seeds. No hydrogen needed!
Balloon-pod milkvetch is native to western North America. It prefers sandy, rocky, or gravelly soil, full sun, and elevations between 2500-12000' (762-3657 m).
Plants: 1½-16" (4-40 cm) in height, typically spreading low across the ground.
Leaves: Leaves are green or silvery (due to fine hairs), and bipinnate or tripinnate. Leaves are ⅞-1½" (2.5-4 cm) in length, and consist of 9-21 leaflets. Each leaflet is oblong to obovate, and ⅛-⅜" (6-10 mm) long.
Flowers: Dense racemes of 5-20 flowers, each up to ½" (1.5 cm) long. Flowers are tubular, bell-shaped, and pinkish, lavendar purple, or yellowish, up to ⅜" (1 cm) long. They appear from May to September.
Fruits: The “balloons” are ⅞-1" (2.5-3 cm) long, and sort of pear-shaped—if you have seen a lady’s slipper, the shape of the flower is similar. Pods are translucent, with very thin walls, and covered with irregular red-purple blotches, occuring in clusters. The pods are unmistakable.
Astragalus whitneyi on science.halleyhosting.com
Astragalus whitneyi on biology.burke.washington.edu (great photos)
Astragalus whitneyi on Discover Life
Astragalus whitneyi on calscape.org
Astragalus whitneyi on Calflora
Astragalus whitneyi description by Thomas H. Kent, last updated 11 Jul 2019.