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Prostrate knotweed is a summer-blooming Eurasian exotic that is widespread and ubiquitous across Illinois. One to five 2-3 mm long flowers occur in a cluster at the base of the leaves; the flowers have very short petioles but may appear sessile. Individual flowers have five white or green and white sepals, no petals, five or eight stamens with yellow anthers, and three styles (one for each carpel) fused into a single pistil with a tripartite yellow stigma fringed with short hairs. The fruit develops within the persistant sepals of the flower. Prostrate knotweed is not fussy about its habitat and withstands a fair amount of foot traffic.

Polygonum

Polygonum aviculare

prostrate knotweed [Blooms: Jun-Sep]