Cardamine hirsuta var. formosana Hayata.

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.

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.

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].