Young plants and free floating plant fragments often develop leaflets with fewer than 14 divisions. Note the difference in leaflet shape, number of divisions, and spacing of the divisions between the two species. Although the two species appear quite easy to distinguish in this photograph, many times these characteristics are not so distinctive. Tiny pinkish flowers occur on reddish spikes that stand several inches above the water and submerge when pollination is complete. The stem width of Eurasian watermilfoil almost doubles below the inflorescence.
Lower flowers are pistillate, upper flowers staminate.
Seeds are produced, but seedlings are rare in nature. In situations where water evaporates slowly and the plants gradually become stranded, Eurasian watermilfoil can develop into a land form. The leaves of the land form are smaller, stiffer, and have fewer divisions. If such plants are submerged, new growth with aquatic leaves develops in 7-10 days, but the first leaves formed have relatively few divisions and only later does the number of divisions increase to more than 12 leaflet pairs. Economic Importance Eurasian watermilfoil adversely impacts aquatic ecosystems by forming dense canopies that often shade out native vegetation.