An Illustrated Guide to ARIZONA WEEDS

The University of Arizona Press




SILVERSHEATH KNOTWEED-Polygonum argyrocoleon Steud.

DESCRIPTION-A bright green erect annual, 8 incbes to 3 feet high, reproducing by seeds alone. The wiry corrugated principal stems are enlarged at each joint, and many branched above, forming the flowering stems. The hairless leaves are alternate, lanceshaped or oblong, 1/2 to 2 1/2 inches long, and 1/8 to 1/3 inch broad, with thin dryish silvery sheaths at the base which encircle the stem. These are very conspicuous, shining and whitish at first, but become shredded and tawny in older parts of the plant.

The small pinkish flowers, on very short stalks, occur in clusters of 2 to 5 along the flower stems at the top of the plant. The flowering stems compose about half of the mature plant, and often are more than a foot long. They are slender and leafless, but have small green bracts with white sheaths at the base of each flower cluster. The pinkish flower parts (calyx) surround the fruit until the achene with the enclosed seed is shed. The shiny 3-angled achene, about l/16 inch long, is mahogany colored.

DISTRIBUTION-Silversheath knotweed, an introduction from central Asia, is a weed in alfalfa fields, citrus, lettuce, and other winter vegetable crops in the agricultural valleys of southern Arizona, especially in Maricopa, Pinal, and Yuma counties. It is also very common along roadsides and all types of waste places; 100 to 3,500 feet elevation; flowering November or December to June or July.

Copyright (c) 1972 The Arizona Board of Regents

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