An Illustrated Guide to ARIZONA WEEDS
The University of Arizona Press
BLACK MUSTARD- Brassica nigra (L.) Koch.
DESCRIPTION-All species of Brassica are restricted noxious weeds in Arizona. A stout erect annual, 2 to 6 feet high with a large taproot, which reproduces by seeds. The dark green alternate leaves all have stalks and are either hairless, or have a few scattered stiff hairs. The lower leaves are large, 4 to 16 inches long with one large terminal lobe and one or more pairs of small lobes below; the edges all have small teeth. The uppermost leaves are smaller, narrow and not divided, commonly drooping.
The flowering part at the top of the plant is 1 to 2 or more feet long, with the branches spreading almost at right angles. The bright yellow flowers have 4 petals with yellow veins.
The narrow erect seedpods, 3/8 to 3/4 inch long at maturity, and about 1/12 inch broad, are on short stalks. They are tipped by a slender beak l/8 inch long or less. The pods stand close to the stem, and often overlap one another. The seeds, in 1 row in each half of the pod, are almost oval, dark reddish brown or nearly black, about 1/16 inch long, with the surface minutely pitted.
DISTRIBUTION-Black mustard was introduced from Eurasia. It is common in spring grain fields and other early crops, pastures, gardens, roadsides, and river-bottoms throughout most of Arizona; 100 to 8,300 feet elevation; flowering March to October. This plant is the principal source of table mustard.
Copyright (c) 1972 The Arizona Board of Regents