Overview
Polygonum arenastrum, oval-leaf knotweed or common knotgrass, is a low, mat-forming annual in the family Polygonaceae. Its wiry, much-branched stems lie flat along the ground or rise slightly at the tips, spreading 4-24 inches (10-60 cm) across and forming dense prostrate patches. The small, oval to elliptic blue-green leaves are 0.2-0.8 inch (5-20 mm) long and arranged alternately, each node sheathed by a silvery, papery membrane (the ochrea) characteristic of the knotweed family. From early summer into autumn tiny flowers about 0.1 inch (2-3 mm) wide sit in clusters of one to four in the leaf axils; they have no true petals, the five greenish tepals being edged in white or pink. Each flower yields a small three-angled brown nutlet. It is a pioneer of compacted, disturbed, and trampled ground, colonising path edges, gateways, driveways, and waste places where competition is low. Tolerant of compaction and drought, it nonetheless completes its life in a single season and dies with the first hard frosts. It is widely treated as a weed of paths, lawns, and arable margins.
Native Range
Polygonum arenastrum is native to Europe and temperate Asia and has spread as an introduced weed to North America, Australia, and much of the temperate world. It grows on bare, compacted, and disturbed ground from sea level to the lower mountains.Suggested Uses
It has little ornamental use and is chiefly encountered as a wild colonist of bare, compacted ground. The seeds and foliage are eaten by birds and small wildlife, and the mats give early cover on disturbed soil.How to Identify
Appearance
Size & Dimensions
Height1" - 4"
Width/Spread4" - 2'
Bloom Information
Flowering runs from June through October, with tiny axillary flowers opening a few at a time over a long season. The greenish tepals edged in white or pink are barely 0.1 inch (2-3 mm) wide and largely self-pollinated. Small three-angled nutlets ripen continuously through summer and autumn, scattering near the parent plant.
Detailed Descriptions
Flower Description
greenish edged white or pinkFoliage Description
blue-greenGrowing Conditions
Sun Requirements
Requires 6-12 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight
Water & Climate
Water Needs
Drought Tolerance
Drought tolerant when established