Common Knotweed

Common Knotweed
Common Knotweed. Polygonum arenastrum.
Polygonaceae, the buckwheat, smartweed or knotweed family.

Plant: Prostrate, weedy, spreading plant, often forming mats 12" or more across, with tiny, green to white or pinkish flowers in the leaf axils. Annual or sometimes short-lived perennial.
Flowers: Tiny, green to white or pinkish, about 1/8", solitary in leaf axils. Petals are absent, five petal-like sepals are green towards the center with white or pinkish edges.
Leaves: Alternate, ovate, 1/4"-3/4", blue-green, with rounded tips,very short petioles, and smooth margins. Sheath where leaves or branches emerge are short, brown, and give the stem a jointed appearance.
Fruit: A small, dark-brown achene.
Blooming: August-October
Habitat: Open areas with compacted soil, driveways, sidewalk cracks, yards.

Comments: Introduced from Europe, and naturalized across North America, this highly variable plant is classified as an invasive weed in many areas. It is known by several colloquial names, including Common Knotweed, Oval-leaf Knotweed, Doorweed, Matweed, and Prostrate Knotweed. The leaf sheathes, characteristic of the buckwheat family, are dark brown, giving the stem a jointed appearance that provides the common name Knotweed.

Where to find it: Around the lodge in hard-packed soil and sidewalk and driveway cracks.