Flower:

Flowers are single and stalkless in the leaf axils all along the stem. The calyx is cup-shaped, green to reddish brown, up to ¼ inch (2.5 to 4.5 mm) long with 4 spreading, sharply pointed, triangular lobes that are half to nearly equal the length of the calyx tube. The 4 stamens arise between the 4 lobes of a nectary disc, with a single club-shaped style in the center. At the base of the calyx is a pair of lance-linear, leaf-like bracts that are as long or longer than the calyx tube.

Leaves and stems:

Plant is glossy smooth throughout. Leaves are simple and alternate, lance elliptic and stalkless, 1½ to 4+ inches (3.5 to 11 cm) long, less than ½ inch wide, the edges toothless but often rough textured. Stems are erect and branched mostly on the lower half with sporadic branches above and stolons at the base, weakly 4-angled, green or tinged with reddish brown.

Fruit:

Fruit is cylindrical, though may be wider at the top, up to ¼ inch (4 to 7 mm) long with persistent calyx lobes and weakly 4-angled sides.

Notes:

False Loosestrife is a wetland species of the Midwest, with scattered populations in the east-central and southeast counties of Minnesota. It appears to have a preference for the peat and sand meadows and shore lines of small lakes and ponds in the Anoka sandplain and similar habits of the Mississippi River flood plain. There are only a few species that may initially confuse its identification (at least the flower), several of which share its range and habitat: Grand Redstem (Ammania robusta), Toothcup (Rotala ramosior) and the related Water Purslane (Ludwigia palustris). The most obvious and defining distinction is that False Loosestrife is the only one with alternate leaves, the others all have opposite leaves.