jointweed

from The Century Dictionary.

• noun Polygonum articulatum, an American plant: so called from its many-jointed spike-like racemes.
• noun A. name of a species of Equisetum.
• noun The mare's-tail, Hippuris vulgaris.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Bot.) A slender, nearly leafless, American herb (Polygonum articulatum), with jointed spikes of small flowers.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Any member of the genus Polygonella of knotweeds and smartweeds.