Cardamine hirsuta L.
Hairy Bittercress, Pepperweed, Shotweed, Snapweed
Hairy bittercress is an introduced species, now generally considered a weed. They exploded into being, seemingly all at once, taking over a good portion of my lawn. Barbara Williams of Nampa, ID reports seeing this in Idaho, outside of its previously recorded range.
Identification: Plants are 8-12" (20-30 cm) high. Leaves at the base are rounded, in opposing pairs, very close to the ground. Tall stems support a few narrower leaves, and tiny clusters of white flowers. Each flower is less than ⅛" (3.2 mm) around; clusters are about ¼" (8.3 mm) around. Each stem also supports multiple upward-pointing seed pods called siliques, each about ¾-1¼" (1.9-3.2 cm) long and less than ¹/₃₂" (1 mm) in diameter. Pods are a reddish purple color, containing multiple seeds. The pods are “explosively dehiscent,” that is, the dry pods pop apart when touched, launching seeds up to 3' (1 m).
Edibility: Flowers and leaves are edible, with a hot flavor (as with other cresses); they are usually used as a garnish on salads.
Cardamine hirsuta on Missouriplants.com
Cardamine hirsuta at Illinois Wildflowers
Cardamine hirsuta on the Virginia Tech Weed Identification Guide
Cardamine hirsuta on Plants for a Future, a resource and information centre for edible and otherwise useful plants
Cardamine hirsuta on Wikipedia
Cardamine hirsuta on Turner Photographics' Wildflowers site
Cardamine hirsuta on SEINet—the Southwest Environmental Information Network
Cardamine hirsuta on eFloras
Cardamine hirsuta description by Thomas H. Kent, last updated 6 Jun 2017.