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.
Plants: 8–12″ (20–30 cm) high.
Leaves: 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.
Flowers: Each flower is less than ⅛″ (3.2 mm) around; clusters are about ¼″ (8.3 mm) around.
Fruits: 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).
Habitats: Waste ground, disturbed sites, lawns, roadsides, fields, railroad beds.
Pepperell, MA. 
Clockwise from top center: opened seed pod, flower cluster, underside and top of basal leaves, upper leaves, seed pods (”siliques”) and flowers. 
Edibility: Flowers and leaves are edible, with a hot flavor (as with other cresses); they are usually used as a garnish on salads.
Online References:
4/12/2012 · Tom and Susan’s, Pepperell, Massachusetts 
4/3/2011 · Susan & Raimond’s, Phoenix, Maryland · ≈ 7 × 4½″ (17 × 11 cm) 
3/14/2012 · Susan and Raimond’s, Phoenix, Maryland · ≈ 7 × 6″ (18 × 15 cm) 
4/13/2012 · Tom and Susan’s, Pepperell, Massachusetts · ≈ 17 × 12″ (44 × 29 cm) 
3/13/2012 · New Jersey · ≈ 8 × 7″ (21 × 17 cm) 
4/13/2012 · Tom and Susan’s, Pepperell, Massachusetts · ≈ 11 × 7″ (27 × 18 cm) 
5/9/2010 · Tom and Susan’s, Pepperell, Massachusetts · ≈ 1 × 1′ (41 × 32 cm) 
4/13/2012 · Tom and Susan’s, Pepperell, Massachusetts · ≈ 5 × 4″ (12 × 10 cm) 
| Kingdom | Plantae | Plants, but not fungi, lichens, or algae (from Stearn's Botanical Latin) |
| 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” |
Cardamine hirsuta description by Thomas H. Kent, not updated.
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