Family: Buckwheat (Polygonaceae)
Size: Approx. 0.125 in.
Notes: A summer annual weed (Eurasian import) which can thrive even on poor and compacted soil. The nodes are swollen and sometimes covered by the remnant of a papery sheath. 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.
Erect knotweed plant profile on the USDA Plants server.