Flower:

Flowers are single in the leaf axils, petals obscure or absent with 4 stamens appressed against a single central style. The calyx is green to reddish brown, ¼ inch or less across with 4 spreading, sharply pointed, triangular to lance-shaped calyx lobes that are half to nearly equal the length of the calyx tube. At the base of the calyx are 2 lance-linear bracteoles on opposite sides and 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, 2 to 4 inches long and ½ to ¾ 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 long with persistent calyx lobes and weakly 4-angled sides.

Notes:

While fairly common throughout the Upper Midwest, we were somewhat surprised at the paucity of information on L. polycarpa in both identification and natural history. A wetland species, in 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 in the southeast counties. There are only a few species that may initially confuse its identification (at least the flower), several of which share its range and habitat: Valley Redstem (Ammania coccinea), Toothcup (Rotala ramosior) and most notably 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.