Hairy Bittercress Identification Guide
Identify hairy bittercress by its basal rosette of pinnate leaves, tiny white four-petaled flowers, and exploding seed pods. Includes look-alikes and habitat.
Read the full Hairy Bittercress encyclopedia entry →
Key Identifying Features
Hairy bittercress (Cardamine hirsuta) is a small cool-season winter annual in the mustard family. It forms a tidy basal rosette of compound leaves close to the ground, then quickly bolts a thin flowering stalk topped by tiny white flowers. Its most memorable trait is the explosive seed pod that flings seeds when touched. Despite the name, it is only sparsely hairy.
- Low basal rosette of pinnately compound leaves
- Tiny white, four-petaled flowers in a small cluster
- Slender upright seed pods (siliques) that shoot seeds when ripe
- A cool-season annual that appears in late winter and early spring
Leaves & Stems
The rosette leaves are pinnately compound, made of several pairs of small rounded leaflets along a stalk and a slightly larger terminal leaflet — a layout resembling a tiny ladder. The terminal leaflet is usually the biggest. A few sparse hairs occur on the leaf stalks and edges. Flowering stems rise 3 to 9 inches and bear smaller, narrower leaves; the stems themselves are mostly smooth or only lightly hairy.
Flowers & Fruit
Flowers are very small, white, with four petals in the cross arrangement typical of mustards (Brassicaceae). They cluster at the top of the stalk. As flowering finishes, narrow upright seed pods (siliques) form, held close to the stem and often overtopping the open flowers. When mature and disturbed, these pods burst open and catapult seeds several feet — a key identification clue and the reason the plant spreads so fast.
How to Tell It Apart from Look-Alikes
- Wavy bittercress (Cardamine flexuosa): Very similar but has a wavy stem and usually six stamens versus four in hairy bittercress; it favors wetter sites.
- Shepherd's purse: Has triangular/heart-shaped seed pods rather than the long narrow siliques of bittercress.
- Common chickweed: Has paired simple leaves and star-shaped five-petaled (deeply notched) flowers, not a pinnate rosette.
Where You'll Find It
Hairy bittercress is a familiar weed of nursery containers, garden beds, lawns, sidewalk cracks, and moist disturbed soil throughout temperate regions. It germinates in fall and winter, flowers very early in spring, and completes its life cycle before summer heat. It is often the first weed to flower in late winter.
Quick ID Checklist
- Low basal rosette of pinnate leaves with a larger terminal leaflet
- Tiny white four-petaled flowers
- Slender upright seed pods that explode when touched
- Cool-season annual, flowering very early in spring
- Found in pots, beds, and moist disturbed soil
The exploding siliques over a pinnate rosette make hairy bittercress unmistakable.
Frequently asked questions
Why do the seed pods explode?
The pods (siliques) build up internal tension as they dry. When ripe and disturbed, they split suddenly and fling seeds several feet away, which is how hairy bittercress spreads so quickly through gardens and nursery pots.
What features confirm hairy bittercress?
Look for a low basal rosette of pinnately compound leaves with a larger terminal leaflet, tiny white four-petaled flowers on a thin stalk, and slender upright pods. The combination is distinctive.
When does hairy bittercress appear?
It is a winter annual that germinates in fall and winter and is typically one of the first weeds to flower in late winter and early spring, completing its life cycle before summer.
How is it different from shepherd's purse?
Both are small mustard-family weeds with white flowers, but shepherd's purse has distinctive triangular or heart-shaped seed pods, while hairy bittercress has long, narrow, upright pods that explode when touched.