An Illustrated Guide to ARIZONA WEEDS
The University of Arizona Press
SUNFLOWER, annual sunflower, common sunflower
SUNFLOWER-Helianthus annuus L.
DESCRIPTION-Sunfllower is a tall, robust branched annual, the coarse, rough stems 3 to 7 feet or more high, reproducing only by seed. The rough-hairy leaves are eggshaped or heartshaped, pointed at the tip, the edges usually toothed. They are mostly alterriate, 2 to 13 inches or more long, 1/2 to 6 inches broad, the upper with short stalks, and the middle and lower with stalks to 8 inches long.
The large flower heads are 2 to 5 inches broad. including the bright-yellow ray or marginal flowers ("petals"). The many small central (disk) flowers are tubular, reddish brown, and produce the achenes. The wedgeshaped achenes, about l/8 to l/2 inch long and 1/8 to 1/3 inch broad, are short-hairy only at the summit. They are dark gray with blackish spots and lighter stripes, and produce 2 thin scales at the summit which are deciduous at maturity.
DISTRIBUTION-Sunflower, introduced in Arizona, is native in the Great Plains area. Abundant in moist soils throughout most of the state along roadsides, waste places, abandoned fields, lowlands, barren spots, and ditchbanks where it is often showy and ornamental. Sometimes a serious pest in cultivated crops of sorghum, cotton, citrus orchards, alfalfa, and small grains; 100 to 7,500 feet elevation; flowering March to October or November.
PRAIRIE SUNFLOWER-Helianthus petiolaris Nutt.
DESCRIPTION-Very similar in appearance to the sunflower, but generally more slender and shorter, mostly 1/2 to 3 feet high. The leaves are smaller, narrower, more lanceshaped, and the edges are not usually toothed. The flower heads are smaller, 1 to 2 inches broad with stiff whitish hairs visible in the dark centers. The same general distribution as sunflower, but not as common.
Copyright (c) 1972 The Arizona Board of Regents