The first three species, with few palmately compound or divided leaves are called toothworts, and were placed in Dentaria in Michigan Flora. They appear distinct in our flora, but the distinctions break down elswehere in the world.
Planodes virginicum (L.) Greene (also placed into Arabis and Sibara in some literature) has been collected just south of Michigan in fairgrounds in Indiana and Ohio and likely occurs in the state. It has pinnately divide leaves and looks similar to some Cardamine (and would more or less key to it) but differs in the fruit valves not coiling upon dehiscing, and in the winged seeds.
1. Leaves palmately compound or deeply palmately divided, the cauline only 2 or 3 (or 4 in C. maxima).
2. Each leaf completely or deeply cleft into (3–) 4–7 lanceolate or narrowly elliptic lobes; rhizome constricted at frequent intervals into easily separable roughly cigar-shaped, obscurely toothed segments; peduncle and rachis of inflorescence minutely pubescent.
2. Each leaf consisting of 3 ovate leaflets; rhizome continuous and strongly toothed (somewhat constricted in the very rare C. maxima); peduncle and rachis glabrous or nearly so (except in C. maxima).
3. Rhizome of essentially uniform diameter (except for the prominent teeth); peduncle and rachis glabrous; cauline leaves usually 2, opposite or nearly so.
3. Rhizome with constrictions (but not the series of cigar-shaped tubers of C. concatenata); peduncle and rachis usually at least sparsely pubescent; cauline leaves usually 3–4, alternate.
1. Leaves all simple or pinnately lobed or divided, the cauline often more than 3.
4. Cauline leaves all simple, unlobed (margins entire to irregularly toothed or sinuate); plant from a prominent basal tuber.
5. Distal part of stem and inflorescence glabrous; proximal part of stem glabrous or usually with minute appressed to incurved hairs; petals white; sepals bright green when fresh, becoming yellowish, rarely with a slight flush of purple at tips only.
5. Distal part of stem and inflorescence with sparse to dense spreading hairs at least 0.25 mm long (occasionally glabrous); proximal part of stem glabrous or with some kind of hairs (rarely entire stem glabrous); petals pink to purple (rarely white); sepals ± flushed with purple (becoming brown after long dry).
4. Cauline leaves deeply pinnately lobed or compound; plant without a basal tuber.
6. Leaves with prominent lanceolate ciliate auricles at the base.
6. Leaves without auricles.
7. Petals (8–) 9–14 mm long; leaflets of basal leaves nearly round; stems glabrous, unbranched.
7. Petals ca. 2–3.5 (–4.5) mm long; leaflets of basal leaves usually distinctly longer than broad; stems glabrous or sometimes pubescent, usually ± branched.
8. Petioles of cauline leaves pubescent; leaf blades and often stem up to the inflorescence also ± hispidulous.
9. Stems ± hispidulous up to the inflorescence, usually flexuous and branched distally; stamens 6.
9. Stem glabrous nearly or quite to the base, straight and unbranched above; stamens usually 4.
8. Petioles glabrous; leaves and stem usually glabrous (stem sometimes hispidulous, especially toward base).
10. Cauline leaves with narrowly linear or oblanceolate segments forming distinct leaflets not confluent with the rachis, the terminal leaflet scarcely if at all broader than lateral leaflets; stem and leaves glabrous.
10. Cauline leaves with broad (elliptic to obovate, often somewhat toothed) segments confluent with the winged rachis (the leaf thus deeply pinnatifid rather than compound), the terminal segment usually distinctly broader than the lateral segments; stem (especially toward the base) and margins of leaves occasionally hispidulous.