Flower:

Flowers are single at the top of the stem and arising from leaf axils in the upper half of the plant. Flowers are usually white, sometimes pink, about 1/3 inch across with 4 notched petals. In the center is a white club-shaped style surrounded by 8 stamens of varying lengths.

The 4 sepals cupping the flower are narrowly triangular and shorter than the petals. Between the flower and stalk is a slender ovary over an inch long and slightly wider than the stalk. The sepals, stalk and ovary are all moderately to densely covered in short, straight, soft spreading hairs, usually mixed with sparse gland-tipped hairs.

Leaves and stems:

Leaves are opposite or alternate, mostly narrowly lance-shaped, 1 to 2 inches long, up to about 1/3 inch (3 to 8 mm) wide, blunt at the tip, stalkless or minutely stalked, often with small leaf clumps (fascicles) in the axils. Edges are toothless, fringed with spreading hairs, and may be flat or rolled under (revolute). Surfaces are variously covered in soft, spreading hairs, especially along the midrib on the underside; the upper leaves often mixed with glandular hairs.

Stems are usually single, unbranched to much branched, and covered in short, soft, spreading hairs. Vegetative buds (turions) are not produced.

Fruit:

The ovary elongates up to about 3 inches as it matures, drying to brown then splitting lengthwise from the top down in 2 to 4 segments, the sides curving away and releasing the numerous seeds. Seeds are elliptic, brown, about 2 mm long with a tuft of long white hairs at the tip to carry them off in the wind.

Notes:

Downy Willowherb is found in wetlands mostly in the northern half of the state, and most often in conifer swamps, sedge mats and fens. It is uncommon in Minnesota and currently a Special Concern species in Wisconsin. The Minnesota Willowherbs can be split into 2 groups, based on whether leaves are toothed or not. The toothless group includes Bog Willowherb (E. leptophyllum), Marsh Willowherb (E. palustre) and Downy Willowherb (E. strictum).

Downy Willowherb is distinguished by the lance-linear leaves and short, straight, spreading hairs on stems and leaves, often with at least some glandular hairs on upper leaves and stems; it is more often unbranched or few-branched, less often bushy. Bog Willowherb and Marsh Willowherb both have short, curved, more appressed hairs; the upper surface of Bog Willowherb leaves is hairy where Marsh Willowherb is hairless.