Yellow CorydalisCorydalis flavula
from Missouri Plants and they have very good pictures
Stems - To 30cm tall, multiple from base or simple, from stout taproot, branching above, sub-succulent, angled, erect to ascending, glaucous, reddish.
Leaves - Alternate, glabrous, glaucous, dull green. Lowest leaves petiolate (the petioles to +7cm long), pinnately divided. Ultimate divisions entire, acute to mucronate. Upper leaves sessile or short petiolate, reduced, pinnately lobed. Lobes entire, acute to mucronate.
Flowers - Corolla yellow, irregular. Petals 4, unequal, slightly joined at base. Uppermost petal spurred, to 1cm long, glabrous. Apex of upper petal toothed, undulate, to 5mm broad. Spur to -3mm long, curved downward slightly.
Flowering - April - May.
Habitat - Moist slopes, low woods, ravines.
Origin - Native to U.S.