Cardamine hirsuta (Hairy bittercress)

Cardamine hirsuta L.

Hairy bittercress, pepperweed, shotweed, snapweed

Kingdom	Plantae	Plants, but not fungi, lichens, or algae
Subkingdom	Tracheobionta	Vascular plants—plants with a “circulatory system” for delivering water and nutrients
Division	Magnoliophyta	Flowering plants, also known as angiosperms
Class	Magnoliopsida	Dicotyledons—plants with two initial seed leaves
Subclass	Rosidae	Roses, legumes, proteas, dogwoods, hydrangeas, mistletoes, euphorbias, grapes, many more
Order	Brassicales	Mustard, cabbage, caper, papaya, nasturtiums, many others; most produce mustard oil
Family	Brassicaceae	Mustards, cabbages
Genus	Cardamine	Bittercress (also called Dentaria)—from the Greek kardamon, an herb with pungent leaves
Species	hirsuta	“Hairy”

About plant names...

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).