Cardamine hirsuta L.

Hoary Bitter Cress

Cardamine hirsuta plant

Family - Brassicaceae

Habit - Taprooted annual forb.

Stems - Erect, to 35 cm, green or sometimes purplish in strong sun, terete, typically multiple from the base, usually simple, glabrous or with sparse, spreading hairs near base.

Leaves - Basal leaves usually lush and numerous at flowering time, 3.0-10.0 cm long, short-petiolate, the petioles with spreading hairs, pinnately compoundwith 3-15 glabrous leaflets, the lateral leaflets circular to ovate or obovate, entire or with 1-3 irregular teeth, tapered to a sessile or short-stalked base, this not expanded along the rachis, the terminal leaflet usually broader than the lateral ones. Stem leaves 2-5, 1-5 cm long, pinnately compound with 5-15 leaflets, these linear to oblanceolate or oblong to ovate, sometimes hairy on the upper surface.

Cardamine hirsuta leavesPressed leaves.

Cardamine hirsuta petioleBase of petiole.

Inflorescences - Compact terminal racemes, elongating in fruit.

Cardamine hirsuta inflorescenceInflorescences.

Flowers - Sepals 4, 1.0-2.5 mm long, green. Petals 4, 1.5-4.0 mm long, white. Stamens usually 4. Styles 0.1-0.6 mm long.

Cardamine hirsuta calyxCalyx.

Cardamine hirsuta flowers2Flowers.

Fruits - Siliques 15-25 mm long, strongly ascending to erect. Seeds 0.9-1.3 mm long, oval to oblong in outline, the surface with a fine, netlike or honeycomb-like pattern of ridges and pits, orange.

Cardamine hirsuta fruitsInfructescence.

Flowering - March - April.

Habitat - Waste ground, disturbed sites, roadsides, lawns, fields, railroads.

Origin - Native to Europe.

Lookalikes - Other small-flowered members of the Cardamine genus, e.g. C. parviflora and C. pensylvanica; also Planodes virginica.

Other info. - Steyermark's 1963 Flora of Missouri listed this plant from only a single county in Missouri (Webster). By the time of Yatskievych's 1999 revision of that work, the plant had spread to over a dozen counties, though it was still described as "uncommon." As of this writing in 2019, the plant has been collected from 33 Missouri counties, predominantly in the southeastern half of the state. In most areas of east-central Missouri, the plant has become by far the most commonly encountered member of the genus. Fortunately, it tends to remain in highly disturbed habitats rather than badly invading intact natural communities. It is prevalent in much of the eastern U.S. and also occurs in western coastal states and Canada.

A confident determination of the small-flowered Cardamine species can be difficult. This plant is recognized by having a lush, rosette-like assemblage of lower leaves, which have nearly round leaflets and stiff, spreading hairs at the base of the petioles. The number of stamens is usually (but not always) 4, which differs from the 6 stamens normally found in other members of the genus. The fruits are generally held erect.

C. hirsuta can flower when quite small. The picture below shows a tiny plant typical of how the species looks in an area that gets mowed or has poor soil.

Cardamine hirsuta plant

Photographs taken in Brown Summit, NC., 3-10-03 (DETenaglia); also at Little Lost Creek Conservation Area, Warren County, MO, 3-7-2012, and Weldon Spring Conservation Area, St. Charles County, MO, 3-31-2013 (SRTurner).


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