Similar to Fallopia japonica (Houtt.) Ronse Decr.
There are several native species of Polygonum that resemble Japanese knotweed in the seedling stage. Japanese knotweed is distinguished by greater overall height, and vigorous growth of stout rhizomes.
This plant is a popular ornamental, and many cultivated varieties are produced by the nursery industry. Varieties may be difficult to distinguish, but most share the same invasive characteristics and will respond to the same treatment as the parent plant.