POLYGONACEAE (BUCKWHEAT FAMILY) 



97 



PROSTRATE KNOTWEED 

 Polygonum aviculdre, L. 



Other English names: Doorweed, Knotgrass, Matgrass. 



Native. Annual or perennial. Propagates by seeds. 



Time of bloom: June to October. 



Seed-time: July to November. 



Range: Nearly everywhere in North America, Europe, and Asia. 



Habitat: Cultivated grounds, yards, roadsides, and waste places. 



A social, almost domesticated, weed, seeming to thrive 

 best where most trampled and abused, growing in thick mats 

 along hard-beaten farmyard paths, and in- 

 truding persistently in lawns and garden bor- 

 ders ; it often fringes the stone flags of city 

 sidewalks. 



Stems slender, pale green, faintly ridged, 

 usually prostrate, four inches to nearly two feet 

 in length, branching in all directions from 

 the white, woody, rather deeply boring root. 

 Smaller branches come out at many of the 

 numberless "knots," or joints, which are pale 

 under the sheathing stipules. Leaves bluish 

 green, nearly elliptical in shape, sessile or with 

 very short petioles, a quarter-inch to an inch 

 long. Flowers very small, the calyx five-parted, 

 greenish white with pink margins, sitting 

 solitary or in groups of two or three in the 

 leaf axils ; stamens usually eight, sometimes 

 fewer ; style three-parted. Achenes dull brown, 

 with acute apex and rounded base, three-angled, 

 and minutely ridged. This species and also the 

 one following is often attacked by a white mil- 

 dew. (Fig. 57.) 



FIG. 



57. Pros- 

 trate Knotweed 

 (Polygonum avicu- 

 lare). X J. 



Means of control 



Hoe-cutting or hand-pulling before the first seeds ripen. Dor- 

 mant seeds will supply later crops to be treated in the same way 

 until the ground is clean. 



