Missouri Plants Knotweed   (Polygonum aviculare) Tracheophyta: Angiosperm: Dicot: Buckwheat (Polygonaceae) Non-native plant from Europe Habitat: any full sun area. ID Features: tiny white flowers that grow in the leaf axils. Natural History: Knotweed is an unsightly weed that thrives on packed soils. It is low-growing and has very small flowers. The petals begin pink in color and then turn white.
The information is from: Missouri Wildflowers by Edgar Denison, 5th Edition, Missouri Department of Conservation, ©1998.