When the genus is defined narrowly, Polygonum species are annual or perennial herbaceous plants, rarely shrubby, with much branched stems.

The genus name is usually said to be from the Greek πολυ- (poly-, 'many') and γόνυ (gonu, 'knee' or 'joint'), in reference to the swollen jointed stem.

Discussing the plant he knew as polygonum in 1655, Matthias Martinius referred to Scribonius Largus (who wrote a list of prescriptions around 47 AD) and gave an alternative etymology, based on γόνος (gonos, 'offspring', 'seed'), the meaning of the name then being the Latin foecundus, i.e. 'fecund', 'with many offspring'.

[6] Many members of the family Polygonaceae that are now placed in separate genera were at one time or other placed in Polygonum, including species of Fagopyrum, Fallopia, Persicaria and Reynoutria,[7] and older sources frequently use much wider definitions of the genus.

Within the tribe, it is most closely related to the genera Duma and Atraphaxis, forming the so-called "DAP clade".

[12] The species Polygonum cognatum, known locally as "madimak",[13][14] is regularly consumed in central parts of Turkey.

The idea of such use was also known to Shakespeare, as Beatrice K. Otto pointed out, quoting A Midsummer Night's Dream:[15] Get you gone, dwarf; You minimus, of hindering knot-grass made;