An Illustrated Guide to ARIZONA WEEDS

The University of Arizona Press

SLIMLEAF BURSAGE, bursage ragweed

Illustration

SUNFLOWER FAMILY-Compositae

SLIM LEAF BURSAGE-Ambrosia confertiflora DC. (Franseria confertiflora [DC.] Rydb.)

DESCRIPTION-A very leafy, somewhat bushy perennial, 1 to 3 feet high, reproducing by seed and proliferating by slender, creeping roots. The leaves, often so hairy they appear gray, are divided into narrow lobes that may be further divided into still smaller lobes. They are alternate, and about 2 to 5 inches long.

The many narrow flowering stems, arising at the tips of the branches, are 2 to 5 inches long, and bear many small heads of tiny male flowers, each head enclosed in a drooping green cup. The female heads, densely clustered in the leaf axils below the male heads, are seldom seen until they mature into spiny little burs. These are topshaped, beak-tipped, granular, 1/12 to 1/8 inch long, and armed with 10 to 20 curved spines, about 1/25 inch long, which end in a definite hook. Each bur encloses 1 or 2 achenes.

DISTRIBUTION-Slimleaf bursage is native, growing in dry or moist, rocky, sterile, or fertile soil. Abundant along city streets, highways, waste places, and edges of cultivated fields, also on barren mesas and slopes in southern and central Arizona; less troublesome northward, except in local areas where colonies have become established (e.g. around Flagstaff); 1,000 to 7,000 feet elevation. Flowering from April to November, its pollen is not a serious hayfever hazard.

ANNUAL BURSAGE-Ambrosia acanthicarpa Hook. (Franseria acanthicarpa [Hook.] Coville)

DESCRIPTION-A bushy annual, distinguished from slimleaf bursage by larger burs (1/8 to l/3 inch long) with longer spines (1/12 to 3/16 inch long), which are straight, not hooked at the tip. Very common in sandy soil in northern Arizona, infrequent southward.

SKELETON LEAF BURSAGE, Bur ragweed-Ambrosia tomentosa Nutt. (Franseria discolor Nutt.)

DESCRIPTION-A perennial similar in growth habits to slimleaf bursage, but easily distinguished by its leaves, which are silvery white beneath and green above. In yards and cultivated ground at Flagstaff and Mormon Lake, Coconino County, local in Winslow (Navajo County), and probably in many other areas in northern Arizona; at 5,000 to 7,500 feet elevation. Although known to cause nitrate poisoning in livestock, the extent or losses (if any) in Arizona is unknown.

Copyright (c) 1972 The Arizona Board of Regents



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