1. Corydalis DC. (corydalis)

Plants annual or occasionally biennial (perennial elsewhere), with taproots. Stems loosely to strongly ascending. Leaves alternate, sometimes also basal, long-petiolate toward the stem base, grading into short-petiolate or sessile toward the stem tip. Leaf blades 2 or 3 times compound and lobed, oblong lanceolate, lanceolate, ovate, or ovate-triangular in outline (often on the same plant), the ultimate segments linear to narrowly oblong or narrowly lanceolate, occasionally elliptic to obovate, mostly sharply pointed at the tip, green or pale and glaucous. Inflorescences 1–15 cm long, usually relatively short-stalked and relatively densely (1–)4–30-flowered. Flowers bilaterally symmetrical in only 1 longitudinal plane, the stalks 1–15 mm long, ascending at flowering but sometimes spreading or pendant at fruiting, without a pair of bractlets. Sepals 1–2(–3) mm long, ovate to ovate-triangular or occasionally somewhat heart-shaped, attached basally, rounded to nearly truncate or occasionally somewhat cordate at the base, the margins entire or less commonly with several coarse, jagged teeth, membranous and white to pale yellow. Corollas pale to bright yellow, sometimes becoming reddish-tinged with age. Inner petals linear or nearly so toward the base, oblanceolate to spatulate above the midpoint with an inconspicuous keel, rounded at the concave tip. Outer petals dissimilar; the lower petal narrowly oblong to oblong-obovate, keeled or with a low irregular median wing (crest), the margins winged toward the usually somewhat spreading (except in cleistogamous flowers) tip; the upper petal with a short to long spur (this often absent or nearly so in cleistogamous flowers), slightly incurved, keeled or with an irregular median wing (crest), winged toward the usually abruptly spreading (except in cleistogamous flowers) tip. Style persistent, slender to relatively stout, the stigma 2-lobed, flattened and somewhat fan-shaped, with 4 or more commonly 8 winglike papillae. Fruits capsules, dehiscent (sometimes tardily so), 10–30 mm long, narrowly oblong-ellipsoid (tapered at each end, beaked at the tip), straight or curved, the surface not swollen over the seeds, smooth or appearing mealy (in C. crystallina), 3- to numerous-seeded. Seeds 1.4–2.3 mm long, somewhat flattened, more or less kidney-shaped in outline, rounded or bluntly to sharply angled along the rim, sometimes with a minute marginal ridge, the surface smooth or appearing finely pebbled, black, shiny, the elaiosome an irregular, somewhat conic, white mass attached in the notch, sometimes poorly developed. About 300 species, North America, Europe, Asia, Africa.

As in other members of the Fumariaceae, the inner petals of Corydalis species are cupped around the anthers and stigmas, and pollen grains are shed onto the stigma. However, most species of Corydalis are visited by a variety of insects (especially bumblebees) and thus are likely to be mostly or at least partly cross-pollinated (see the treatment of Dicentra for a similar pollination mechanism). This situation has not been studied in detail in most of the North American species. Macior (1978a, b) noted visitation of C. flavula flowers by queens of two species of bumblebees, but also determined that flowers bagged to exclude all insects still produced fruits. Thus, self pollination may be the main mode of reproduction in C. flavula. Additionally, plants of some species of Corydalis (in Missouri, principally C. flavula and C. micrantha) can produce inflorescences with some or all of the flowers cleistogamous. Such inflorescences tend to be short (often reduced to clusters rather than racemose). The tips of the outer petals do not spread and the spur is very short or absent.

Although specimens of Corydalis are most easily observed in the field when in flower, some species are best distinguished by their fruits and seeds. The best time to collect specimens is when both flowers and mature fruits are present. The size ranges for corolla lengths in the key to species include the spur in the measurement.

In addition to the species treated below, C. curvisiliqua (A. Gray) Engelm. ex A. Gray ssp. grandibracteata (Fedde) G.B. Ownbey should be searched for in northeastern and southeastern Missouri. This taxon is known from sand prairies in southeastern Iowa and western Illinois (Tyson and Ebinger, 1999) and also is found in sandy habitats from Kansas to Texas. It is most similar to C. aurea, but differs in having seeds that are roughened rather than pebbled (observed with magnification as having minute, blunt, tubercles rather than polygonal facets) and relatively conspicuous inflorescence bracts (the lowermost bracts 10–15 mm vs. 4–10 mm long).