Description from Flora of China
Barbarea arisanensis (Hayata) S. S. Ying; Cardamine arisanensis Hayata; C. debilis D. Don (1825), not Banks ex de Candolle (1821); C. flexuosa subsp. debilis O. E. Schulz; C. flexuosa subsp. debilis var. occulata (Hornemann) O. E. Schulz; C. flexuosa var. debilis (O. E. Schulz) T. Y. Cheo & R. C. Fang; C. flexuosa var. ovatifolia T. Y. Cheo & R. C. Fang; C. hirsuta Linnaeus var. flaccida Franchet; C. hirsuta subsp. flexuosa (Withering) J. D. Hooker; C. hirsuta var. omeiensis T. Y. Cheo & R. C. Fang; C. hirsuta var. sylvatica (Link) Syme; C. occulata Hornemann; C. scutata Thunberg subsp. flexuosa (Withering) H. Hara; C. sylvatica Link; C. zollingeri Turczaninow; Nasturtium obliquum Zollinger.
Herbs annual or biennial, (6-)10-50 cm tall, sparsely to densely hirsute basally or throughout, or glabrous. Stems erect, ascending, or decumbent, 1 to several from base, simple or branched, flexuous or straight. Basal leaves not rosulate, often withered by anthesis, petiolate; leaf blade (2-)4-10(-14) cm, lyrate; terminal lobe reniform, broadly ovate, or suborbicular, repand or 3-5-lobed; lateral lobes, (1 or)2-6(or 7) on each side of midvein, petiolulate or subsessile, oblong, ovate, or elliptic, smaller than terminal lobe, entire, repand, crenate, or 3(-5)-lobed. Cauline leaves 3-15, including petiole (2-)3.5-5.5(-7) cm; petiole base not auriculate; terminal lobe 3-5-lobed; lateral lobes 2-7 on each side of midvein, suborbicular, ovate, oblong, oblanceolate, or linear, similar to or slightly smaller than terminal lobe, sessile or shortly petiolulate, entire, repand, dentate, or 3(-5)-lobed. Fruiting pedicels divaricate or ascending, (5-)6-14(-17) mm, slender. Sepals oblong, 1.5-2.5 × 0.7-1 mm. Petals white, spatulate, 2.5-4(-5) × 1-1.7 mm. Stamens 6, rarely 4 and lateral pair absent; filaments 2-3 mm; anthers ovate, 0.3-0.5 mm. Ovules 18-40 per ovary. Fruit linear, (0.8-)1.2-2.8 cm × 1-1.5 mm; valves glabrous, torulose; style 0.3-1(-1.5) mm. Seeds brown, oblong or subquadrate, 0.9-1.5 × 0.6-1 mm, narrowly margined or not. Fl. Feb-May, fr. Apr-Jul. 2n = 32.
The above first records from Myanmar and Thailand are based on Keenan et al. 3918 (E) and Maxwell 90-149 (MO), respectively.
Cardamine flexuosa is one of the most variable species of Brassicaceae, especially in stem direction, plant height, density of indumentum, flower size, degree of zigzagging of the raceme rachis, orientation of fruiting pedicels and, most dramatically, number, shape, size, base (sessile vs. petiolulate), and margin of lateral leaf lobes. Although Schulz (Bot. Jahrb. Syst. 32: 464-473. 1903) recognized 20 infraspecific taxa in C. flexuosa, an examination of the types of most of these reveals that he confused the limits of least four different species, including C. parviflora, C. scutata, and the North American C. pensylvanica Muhlenberg ex Willdenow. Only a small fraction of the vast number of variants of C. flexuosa have been accorded infraspecific ranks, but all of those occur sporadically throughout the range of the species, and the present authors prefer to avoid the recognition of infraspecific taxa that are based on unreliable characters, especially the morphology of lateral leaf lobes.
Although Cardamine occulata was based on Chinese material, it was not mentioned in FRPS, and it represents only a minor variant of C. flexuosa.
Cardamine flexuosa is used medicinally.
Fields, roadsides, grasslands, disturbed sites, streamsides, clearings, running water, wet forests, dry sites, greenhouses; near sea level to 3600 m. Throughout China [Bangladesh, Bhutan, India, Indonesia, Japan, Kashmir, Korea, Laos, Malaysia, Myanmar, Nepal, Pakistan, Philippines, Sikkim, Thailand, Vietnam; native to Europe; naturalized in Australia and North and South America].