Hairy Bitter Cress is one of several weedy plants in the Mustard family that is native to Eurasia. It closely resembles several other species in the Mustard family, including Sibara virginica (Virginia Rock Cress), Cardamine parviflora arenicola (Small-Flowered Bitter Cress), Cardamine pensylvanica (Pennsylvania Bitter Cress), and Cardamine flexuosa (Wavy Bitter Cress). Unlike Small-Flowered Bitter Cress and Pennsylvania Bitter Cress, Hairy Bitter Cress has hairy petioles (particularly the basal) and the base of its flowering stalk is often hairy. Unlike Virginia Rock Cress, it has basal leaflets that are about as long as across (orbicular, oval) and its seeds lack winged margins. Unlike Wavy Bitter Cress, it has persistent basal leaves and a flowering stalk that becomes hairless above the bottom portion. The flowers of Hairy Bitter Cress have 4 stamens, while the flowers of Wavy Bitter Cress have 6 stamens. All of these plants are winter annuals or biennials.

This non-native plant is a winter annual or biennial. Initially, it forms a low rosette of basal leaves spanning up to 8" across. Each basal leaf is up to 4" long, ¾" across, and simple-pinnate, consisting of 5-9 leaflets and a long petiole. The basal leaflets are orbicular to oval in shape and slightly undulate along their margins; the outer leaflets are larger in size than the inner leaflets. The basal petioles often have a few long hairs along their margins and they are often dull purple. From the center of the rosette, there develops a flowering stalk up to 10" tall that is unbranched or sparingly branched; this stalk is light green to dull purple and hairless, except for a few long hairs toward its base. About 3-5 cauline leaves alternate along the stalk. The cauline leaves are similar to the basal leaves, except they are shorter in length and their leaflets are more narrow (linear-oblong to ovate-oblanceolate). Sometimes long hairs are present along the margins of the cauline leaflets and near the base of the cauline petioles. The central stalk (and any secondary stalks) terminates in a raceme of flowers. The flowers bloom near the apex of the inflorescence, while the seedpods develop below. Each flower is less than ¼" across, consisting of 4 white petals, 4 sepals, 4 stamens, and a pistil with a single style. The sepals are light green to dull purple, oblong in shape, and either hairless or slightly hairy; they are shorter than the petals. The blooming period occurs from early to mid-spring and lasts about a month. Each flower is replaced by a narrowly cylindrical seedpod (silique) up to 1" long. The seedpods are light green to dull purple, hairless, and ascending; they have stout pedicels up to ½" long. Each seedpod contains several small seeds that are ovoid, somewhat flattened, and wingless along their margins. The root system is shallow and fibrous. This plant spreads by reseeding itself.

Cardamine hirsuta L.:
Argentina (South America)
Colombia (South America)
Ecuador (South America)
Gabon (Africa & Madagascar)
India (Asia)
Japan (Asia)
Laos (Asia)
Mexico (Mesoamerica)
Madagascar (Africa & Madagascar)
Peru (South America)
Philippines (Asia)
Pakistan (Asia)
United States (North America)
South Africa (Africa & Madagascar)
China (Asia)
Sri Lanka (Asia)
Vietnam (Asia)
Turkmenistan (Asia)
Thailand (Asia)
Panama (Mesoamerica)
Venezuela (South America)

Cardamine hirsuta var. hirsuta :
China (Asia)

Canada

Origin: Exotic

Regularity: Regularly occurring

Currently: Unknown/Undetermined

Confidence: Confident

United States

Origin: Exotic

Regularity: Regularly occurring

Currently: Unknown/Undetermined

Confidence: Confident

Distribution: Cosmopolitan.

Hairy Bitter Cress is still rather uncommon in Illinois; it is more likely to to be encountered in the NE and southern sections of the state than elsewhere (see Distribution Map). This weedy plant was introduced from Eurasia. Habitats consist of cropland, old fields, margins of paths, roadsides, and waste areas. Habitats with a history of disturbance are preferred.

A highly variable species, especially with respect to plant size, density of indumentum, number, shape, size, and margins of lateral leaf lobes, and flower morphology (e.g., presence vs. absence of petals and stamen number). The species has been divided into more than 15 subspecies, varieties, and forms. However, all of these taxa are based on characters that can be highly variable even within the same population. Only one synonym pertinent to China is cited above. For additional synonymy, the reader should consult Schulz (Bot. Jahrb. Syst. 32: 464-473. 1903).

Most of the specimens identified as Cardamine hirsuta in the Chinese herbaria consulted by the present authors belong to C. flexuosa. The two species can be separated easily by the above key. Furthermore, about 80% of the plants of C. hirsuta have flowers with four stamens and 18% have five, whereas about 97% of those of C. flexuosa have six stamens.

Annual herb, 10-30 cm tall, erect, often with a basal rosette of leaves only and a slender tap root. Basal leaves 2-7-jugate, 2-10 cm long, 1-2.5 cm broad, glabrous or hairy with simple hairs; leaflets ovate-orbicular, except the terminal one which is slightly larger and subreniform, shortly stalked, subsessile to sessile, very variable in size, subentire to irregularly few lobulate and toothed, usually 6-10 mm in diam. Racemes 10-30-flowered, up to 10 cm long in fruit. Sepals 2-2.5 mm long. Petals c. 3 mm long, usually not or hardly exceeding the sepals (very rarely suppressed). Stamens 6, rarely 4 (the outer 2 abortive ), c. 2: 2.5 mm long. Siliquae linear, compressed, 15-25 mm long, 1 mm broad, straight, glabrous ; valves smooth with a faint mid-vein; style almost absent to 0.5 mm long with a capitate stigma; septum not veined; seeds many, c. 1 mm long.

Fairly common in our northern hills, but seems to be under collected. Some forms may pass on to the previous species.

Herbs annual, (3-)10-35(-45) cm tall, sparsely hirsute at least along petioles of basal leaves, often glabrous above. Stems erect, ascending, or decumbent, 1 to several from base, simple or branched above, not flexuous. Basal leaves rosulate; petiole ciliate, 0.5-5 cm; leaf blade (1.5-)2.5-10(-13) cm, lyrate-pinnatisect; terminal lobe reniform or orbicular, 0.4-2 × 0.6-3 cm, margin entire, repand, dentate, or 3-5-lobed; lateral lobes (1-)3-7(-11) on each side of midvein, petiolulate, oblong, ovate, obovate, or orbicular, smaller than terminal lobe, entire, repand, crenate, or 3-lobed. Cauline leaves 1-4(-6), rarely absent, shortly petiolate, including petiole (0.5-)1.2-5.5(-7) cm; petiole base not auriculate; lateral lobes (2-)4-7(-10) on each side of midvein, ovate, oblong, oblanceolate, or linear, sessile or shortly petiolulate, entire, repand, or dentate. Fruiting pedicels erect or ascending, (2-)3-10(-14) mm, slender. Sepals oblong, 1.5-2.5 × 0.3-0.7 mm. Petals white, spatulate, 2.5-4.5(-5) × 0.5-1.1 mm, sometimes absent. Stamens 4 and lateral pair often absent, rarely 5 or 6; filaments 1.8-3 mm; anthers ovate, 0.3-0.5 mm. Ovules 14-40 per ovary. Fruit linear, (0.9-)1.5-2.5(-2.8) cm × (0.8-)1-1.4 mm; valves glabrous, torulose; style 0.1-0.6(-1) mm. Seeds light brown, oblong or subquadrate, 0.9-1.3(-1.5) × 0.6-0.9(-1.1) mm, narrowly margined. Fl. Feb-May, fr. Apr-Jul. 2n = 16.

Cardamine hirsuta var. formosana Hayata.

Mountain slopes, roadsides, fields, clearings, wastelands, damp places, grassy areas; near sea level to 3000 m. Throughout China [India, Indonesia, Japan, Laos, Malaysia, New Guinea, Pakistan, Philippines, Sikkim, Sri Lanka, Thailand, Turkmenistan, Vietnam; SW Asia, Europe; naturalized in S Africa, Australia, North and South America].

Hairy Bitter Cress is still rather uncommon in Illinois; it is more likely to to be encountered in the NE and southern sections of the state than elsewhere (see Distribution Map). This weedy plant was introduced from Eurasia. Habitats consist of cropland, old fields, margins of paths, roadsides, and waste areas. Habitats with a history of disturbance are preferred.

Foodplant / open feeder
gregarious larva of Athalia liberta grazes on leaf (underside) of Cardamine hirsuta

In Great Britain and/or Ireland:
Foodplant / parasite
colony of sporangium of Peronospora parasitica parasitises live Cardamine hirsuta
Remarks: season: 1-4

Foodplant / parasite
amphigenous colony of Ramularia hyphomycetous anamorph of Ramularia cardamines parasitises live leaf of Cardamine hirsuta

The nectar and pollen of the flowers probably attract small bees and flies. The caterpillars of the butterfly Anthocharis midea (Falcate Orangetip) and the moth Evergestis pallidata (Purple-Backed Cabbageworm) feed occasionally on Cardamine spp. Photographic Location: Along a gravelly path at Kickapoo State Park in Vermillion County, Illinois.

Fl. Per.: March-May.

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 6
Species: 10
Species With Barcodes: 1

Canada

Rounded National Status Rank: NNA - Not Applicable

United States

Rounded National Status Rank: NNA - Not Applicable

Rounded Global Status Rank: GNR - Not Yet Ranked

Successful development is promoted by full to partial sunlight, moist to mesic conditions, and a somewhat barren soil containing gravel or clay. However, this weedy plant will adapt to fertile loam and sandy soil as well. Most growth and development occurs during the early spring when temperatures are cool and moisture is abundant.