Like many milfoils, Eurasian watermilfoil is a submersed perennial plant with finely dissected feather-like leaves and thin stems. The leaves are arranged in whorls of 4 (rarely 5) around the stem at each node. Each Eurasian watermilfoil leaf generally has 14 or more leaflet pairs and this feature can be used most of the time to distinguish Eurasian watermilfoil from other milfoil species that have whorls of 4 leaves but fewer than 14 leaflet pairs. However, the number of pairs of leaf divisions is highly variable, with younger plants and growing fragments often having fewer than 14. The tips of Eurasian watermilfoil that emerge from the water are often red—especially early in the growing season—
and these reddish spikes stand several inches above the water and submerge when pollination is complete. Flowers are tiny and pink; lower flowers are pistillate and upper flowers are 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.
Note the finely compound leaves.
The emergent tip develops into the inflorescence and does not carry leaves.