All Corydalis species are delicate, low-growing, and sometimes form mats. Flowers are in terminal racemes with a few florets, each light yellow, the petals converging (but not fused) into a tubelike appearance with a spur; the supporting stem attached near the center of the flower rather than at the end. Blooms April–May. Leaves are similar to Dutchman’s breeches; compound, with fernlike, dissected divisions, carried on flowering stems and arising from the base, bluish green.
There are four species of Corydalis in Missouri, and they are quite similar in appearance.
- Pale corydalis (C. flavula) has smaller flowers than the others (about 3/8 inch long), with an incurved (not straight) floral tube; the flower stalks are 3/8–3/4 inch long, longer than all our other species. It is the most abundant corydalis in Missouri. Compared to our other species, it prefers moister, richer soils in shadier locations.
- Small-flowered corydalis (or slender fumewort, C. micrantha) is the second most common corydalis in the state. Compared to C. flavula, it has larger, straighter flowers with a larger spur and shorter leaf stalk. Use a hand lens, and you'll see the surfaces of the seeds are finely pebbled (not smooth). It's scattered statewide; one subspecies (australis) is found only in sandy places in the Bootheel.
- Golden corydalis (C. aurea) is uncommon; it is also widely scattered, mostly south of the Missouri River, and usually grows in acidic soils in glades, upland prairies, and dry forest openings. Like C. micrantha, its flowers are larger, straighter, with a larger spur and shorter leaf stalk than that of C. flavula. C. aurea's flowers are larger than those of C. micrantha, though, and the surfaces of the seeds are smooth (not pebbled).
- Mealy corydalis (C. crystallina) is scattered in western Missouri, mostly south of the Missouri River, and lives in acidic soils of glades, upland prairies, and roadsides. It is similar to C. micrantha and C. aurea, but its fruits are covered with short, white, bladderlike inflated hairs, making it look mealy. Also, although the other corydalis species flowers range from pale yellow to bright yellow, this species' flowers are always bright yellow.