TUMBLE MUSTARD, Sisymbrium
altissimum L. 1, lower leaf; 2, root; 3, upper
part of plant; 4, seed; 5, seed pod. Annual or winter
annual, reproducing by seed, taprooted. Stem erect, 2 to
5 feet (0.6 to 1.5 m) tall, bushy, branching. Stem and branches
smooth above, somewhat hairy below, pithy. Leaves pale green. Lower
leaves are large and divided; upper leaves have smaller narrow segments.
Flowers yellowish-white, 1/4 to 1/2 inch (6 to 13 mm) in diameter,
4-petaled, growing in numerous but short racemes. Seed pods
stiff, narrow, 2 to 4 inches (5 to 10 cm) long, divided into 2 parts; look
like long stems rather than seed pods. Seeds oblong, about 1/16
inch (1.5 mm) long, dark reddish-brown. Found in small grains and
waste places. Stem often breaks off at maturity causing the plant to be
blown about by wind.