Japanese hedge parsley is considered a winter annual (germinating in fall) or a biennial. The first year plants have finely divided fern-like leaves in a rosette near the ground. White umbel flowers develop into small seeds with burrs that catch on fur and clothing. Fall and winter is a good time to search for this plant since the rosettes that germinate in fall remain green and overwinter under the snow.
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For more information on this new threat or to learn about others, visit Wisconsin Department of Natural Resources.