POLYGONACEAE
Polygonum arenastrum Boreau
(common knotweed, doorweed)

Maple Spring, Contra Costa Co.
Coll. Mary L. Bowerman
October 4, 1930
UC Herbarium #692128
UCMP-SFES #63

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Morphology, Distribution, and Habitat (After Mason, 1957 and Hickman, 1993)

The achene is 2-3 millimeters, trigonous, at maturity generally two sides are convex and about one is concave. It is closely enveloped by the perianth, microscopically glandularly-roughened, and dull-dark brown. The plant is a common weed of many habitats, abundant in disturbed places, often on the borders of marshes and ponds, recently emerged floodlands, and the borders of tidal salt marshes.