Family: Buckwheat (Polygonaceae)
Size: Approx. 0.125 in.
Other names: Prostrate knotweed, oval knotweed
Notes: A summer annual weed (Eurasian import) which can thrive even on poor and compacted soil. The mature plant grows prostrate to erect with slender, tough stems, which are extensively branched, giving it a zigzag appearance. 17 species of Polygonum in Arizona.
Knotweed entry in the online edition of An Illustrated Guide to Arizona Weeds, Kittie F. Parker, University of Arizona Press.
Entry for common knotweed in the University of California Statewide Integrated Pest Management Project.
Oval knotweed plant profile on the USDA Plants server.