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Wild mustard's upper stems end in racemes of 1/2" wide yellow flowers. Each flower has four yellow petals, six yellow stamens, and a single green pistil. After fertilization, the pistil elongates into a thin, cylindrical silique (seedpod), 1/2-1.5" long, filled with tiny (2 mm diameter) brown or black seeds; the distal third of the silique is a ridged or square "beak". The seeds are reported to remain dormant but viable in the soil for up to 60 years.

Sinapis

Sinapis arvensis

wild mustard [Blooms: May-Jun]