a polygonaceous weedy plant, Polygonum aviculare, whose small green flowers produce numerous seeds
2.
any of several related plants
knotgrass in American English
(ˈnɑtˌgræs)
noun
1.
any of several weedy plants (genus Polygonum) of the buckwheat family; esp., a common weed (P. aviculare) with slender stems, narrow leaves, and small axillary flowers
: often called ˈknotˌweed (ˈnɑtˌwid)
2. US
a creeping grass (Paspalum distichum) growing in wet places in the S U.S.