Knotgrass definition

A low-growing, weedy grass (Paspalum distichum) with spikelets arranged in two rows along the rachis.

Any of several weedy plants of the genus Polygonum having stems with nodes.

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.

A creeping grass (Paspalum distichum) growing in wet places in the S U.S.