Family - Brassicaceae

Stems - To +60cm long(tall), erect to ascending or creeping, from taproot and fibrous roots (often rooting at nodes), herbaceous, glabrous, fistulose.

Stem and roots (from nodes).

Leaves - Alternate, odd-pinnate, petiolate, to +15cm long, glabrous. Petiole partially clasping the stem. Leaflets 3-11, opposite to subopposite, sessile, oblique at base, ovate-lanceolate, often emarginate at apex, to +2cm long, +1cm broad, entire to irregularly shallow crenate.

Inflorescence - Compact terminal racemes, quickly elongating in fruit to +20cm long. Pedicels glabrous, 2-7mm long in flower, elongating in fruit.

Flowers - Petals 4, free, white, clawed, glabrous. Claw to 2mm long. Limb rounded at apex, 3mm long, 2mm broad. Stamens 6, with 4 long and 2 short. Shorter staens opposite and outside of longer stamens. Filaments purplish, glabrous, 3.5mm long. Anthers yellow. Ovary terete, purplish-green, 2.5mm long, glabrous. Style very short or wanting, persistent in fruit as beak. Stigma 2-lobed, capitate. Sepals 4, free, glabrous or with a few minute strigose hairs at apex, 3mm long, 1.2mm broad, often with revolute margins. Siliques to +1.5cm long, terete, glabrous, many-seeded.

Flowers close-up.

Fruits.

Flowering - April - October.

Habitat - In water and on wet ground.

Origin - Native to Eurasia.

Other info. - Nasturtium is a fairly common plant throughout the southern half of Missouri but is also found in a few counties north of the Missouri River.
Another species, N. microphyllum (Boenn.) Reichb. is found in the U.S.(not yet in Missouri) and is native to Europe. This species has long slender fruits to +2.5cm.
N. officinaleis an edible plant and was used by Indians to cure many ailments. You should be sure the plant is growing in clean water or on clean soil before you harvest it for food.
When growing in water the plant forms many roots from its nodes and forms large mats as shown above. On land, the plant is a bit more ragged and thin:

Photographs taken at the Parkville Nature Sanctuary, Parkville, MO., 5-12-00, and in Iron County, MO., 5-18-03.