An Illustrated Guide to ARIZONA WEEDS
The University of Arizona Press
PROSTRATE KNOTWEED-Polygonum aviculare L.
DESCRIPTION-A tough, wiry stemmed, prostrate annual that appears perennial, reproducing only by seeds. The stems branch greatly, spreading out from the root in all directions to form mats 1/3 to 4 feet in diameter. They are seldom erect plants as is silversheath knotweed, but the ends may ascend 3 to 9 inches in rich moist soil. The small bluish green leaves are alternate, oblong or lanceshaped, 1/4 to 1 1/2 inches long, about 3/8 inch broad, with a very short stalk, encircled by thin papery sheaths. The leaves may be very close together on the stem or widely spaced, but unlike silversheath knotweed, they occur to the ends of the stems, approximately all the same size.
The small white or greenish flower parts are pinkish tinged. They are arranged in small clusters in the leaf axils on the upper part of the plant, and not in long leafless branches as silversheath knotweed. The achene is 3-angled; the surface, except the angles, is dull, very dark mahogany or blackish, and larger, 1 1/2 to 1/8 inch long.
DISTRIBUTION-Prostrate knotweed, also Eurasian, is very common throughout the state on dry packed soil of walks, yards, doorways, and waste ground where it is a very hardy weed, withstanding trampling and drought. It is also common in more moist soil in lawns, flower beds, cultivated fields, and eroded or overgrazed mountain meadows; 100 to 8,500 feet elevation; flowering principally March to October.
Copyright (c) 1972 The Arizona Board of Regents