Polygonaceous \Pol`y*go*na"ceous\, a. [See Polygonum.]

(Bot.) Of or pertaining to a natural order of apetalous plants (Polygonace[ae]), of which the knotweeds (species of Polygonum) are the type, and which includes also the docks (Rumex), the buckwheat, rhubarb, sea grape (Coccoloba), and several other genera.

Source: Webster's Revised Unabridged Dictionary (1913)