Ontario Weeds: Japanese knotweed
Excerpt from Publication 505, Ontario Weeds, Order this publication
Table of Contents
Name: Japanese knotweed, Polygonum
cuspidatum Sieb. & Zucc.,
Japanese knotweed (A - plants; B - tips of young shoots in spring; C - flowering branch).
Japanese knotweed. A. Hollow stem from branching rhizome. B. Top of flowering stem. C. Winged "seed".
Stems & Roots: Stems erect, 75cm-3m
(2½-10ft) high, branched or unbranched, round, smooth, often
mottled reddish-purple, hollow except at the nodes, dying back to
the ground each winter, arising in early spring and throughout the
growing season from widely spreading, shallow or deeply penetrating,
thick, vigorous, whitish underground rhizomes, the younger rhizomes
whitish except for dark brown, papery sheaths, with distinct nodes
and internodes, the older ones thick, brownish, firm and often somewhat
Similar Species: It is distinguished by its very vigorous growth beginning in early spring and continuing to late autumn, its thick, widely spreading. whitish or brownish rhizomes, its erect stems, often mottled, hollow except at the nodes, its broad leaves with abruptly narrowed tip and a prominent ocrea around the stem at the base of each leafstalk, and its showy bunches of small greenish-white flowers. Two or more similar but smaller and usually less vigorous relatives of Japanese knotweed, presently grown as foundation or ground cover, may occasionally also escape from cultivation.
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