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Genus: Polygonum — knotweed

There are several things that are particularly important when identifying species of Polygonum. First, most New England species make two kinds of fruits in a growing season. The key uses only the summer fruits, which are smaller, and brown to black, while the late-season fruits are olive green in color and significantly larger. Second, notice the relative size of the leaves on the main stem versus the branches. Some species have much larger leaves on the main stem, while others do not. Note also that the leaves are often shed later in the season, leaving only the bracts, which can be much smaller and differ in length to width ratios from the leaves themselves. Third, make sure to measure the length of intact stipules, not ones that have become fibrous. Finally, since the tepals continue to grow as the fruit matures, their length should be measured in fruiting condition. References: Löve and Löve (1956), Costea and Tardif (2003).


Polygonaceae (buckwheat family)

This genus’s species in New England

Visit this genus in the Dichotomous Key