Astragalus whitneyi A. Gray
Balloon-pod milk-vetch, balloon milk-vetch, Whitney's locoweed, 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.
Biology.burke.washington.edu (great photos)
Astragalus whitneyi description by Thomas H. Kent, last updated 25 May 2020.