Watercress is a perennial aquatic plant usually growing submerged in or emerging from water, typically in spring branches and streams in the Ozarks. It can grow like thick green garlands in the water and often forms bushy colonies. It's in the mustard family and apparently was introduced to North America long ago. It is edible, but before eating it, be certain you've identified it correctly, and wash it thoroughly.
The flowers are massed at the tips of stems; they are minute; the 4 tiny petals are white, sometimes tinged with lavender.
Blooms April–October.
The leaves are alternate, clasping the stem with small rounded auricles (earlike appendages). Most leaves are pinnately compound with 3–9 leaflets, with a rounded leaflet at the top and several opposite, rounded leaflets along the leaf axis.
Height: to 10 inches.
Introduced in scattered locations statewide. Most common in Ozark and Ozark border counties of southern and central Missouri.
Habitat and Conservation
Most common in and around the cold waters of springs and spring branches. It also occurs on banks (especially when stranded by a receding waterline) and in fens, marshes, and ditches.
If you visit one of Missouri's big Ozark springs, at any time of year, look for watercress growing like deep green garlands where the spring flows over rocks and riffles.
Watercress can grow as a submerged, floating, or emergent plant. It roots at the stem nodes and grows easily from cuttings. Its ability to spread quickly and grow rampantly is a main reason it can become invasive.
Status
Introduced aquatic plant/wildflower, native to Eurasia. First recorded in New England in the early 1800s. An edible green. Considered noxious or invasive in many US states and internationally.
Watercress has been known to grow so rampantly that it blocks streams and can cause flooding. US states that have listed it as invasive or have recorded it invading natural areas include Oregon, Georgia, Kentucky, West Virginia, Maryland, New Jersey, Connecticut, Rhode Island, and New Hampshire.
Human Connections
Watercress is used as a salad green and has a tangy flavor. You can sometimes find cultivated watercress in grocery stores. If you are foraging, collect it only from uncontaminated sources; pesticide, herbicide, and other toxic runoff may render watercress unsafe to eat. Also, be sure to wash it thoroughly to remove microscopic parasites such as Giardia. Giardia is notoriously present in waters that look crystal clear. Parasite problems, notably from an organism called the common liver fluke (Fasciola hepatica), may be exacerbated in areas with runoff from livestock manure. And of course, be certain you've correctly identified any wild edible before eating.
Many people enjoy seeing its lush greenery on canoe trips; look for it when you're floating Ozark streams like the Current and Meramec. Temper your enthusiasm by the knowledge that it's nonnative and is known to be invasive in North America.
The name "cress" is used for a variety of usually edible, peppery plants in the mustard family.
Botanists have long pondered the origin of watercress: Is it native to North America? For a long time, people pointed to watercress's presence at remote spring branches as evidence that it is native. However, those locations were not as pristine as formerly believed. Today most agree that it is in fact an Old World species that was introduced to North America.
Ecosystem Connections
Humans are not the only ones to eat watercress. Herbivorous fish, birds, and mammals nibble its greens, as do numerous aquatic insects, snails, and more. It also often hosts masses of aphids, which is another reason to wash it well prior to eating it.
Where it grows too abundantly, watercress can be a noxious or invasive plant. See the Status section for information on this subject.
Watercress is one of the plants that remains remarkably green in winter when it lives in the waters of spring outlets. At our big Ozark springs, note how watercress remains green on even the coldest days of the year. In summer, spring water feels refreshingly cold, but in winter it is comparatively warm: it is always about 56F because that is the constant temperature of the ground deep beneath the surface. Thus the water emerging from a spring is much warmer than the super-cold air on a January day, and the submerged watercress stays green and alive.
