Water thyme : See Anacharis.

Example:


Taxonomy
Water-Thyme, Elodea canadensis, weed, Co. Down, country, ponds, ditches, streams, rank, monocotyledonous, natural order, Personal tools, North America, Down, Ireland, England, Hydrocharideae, Territorial Waters, Charles Waterton.

Defination from the web:
Water-Thyme. From LoveToKnow 1911. WATER-THYME, known botanically as Elodea canadensis, a small submerged water-weed, native of North America. It was introduced into Co. Down, Ireland, about 1836, and appeared in England in 1841, spreading through the country in ponds, ditches' and ...