- Name also: Whiteflower Willowherb, Milkflower Willow-herb
- Family: Willowherb Family – Onagraceae
- Growing form: Perennial herb. Subterraneous runners very short, thick overwintering buds right at base of stem.
- Height: 10–30 cm (4–12 in.). Stem unbranched, at base glabrous, higher up streaked with curved hairs.
- Flower: Corolla regular, white (rarely slightly reddish), 3–6 mm (0.12–0.24 in.) long; petals 4, with notched tips. Sepals 4. Stamens 8. Gynoecium fused, a single carpel, stigma club-like; ovaries under tepals, with glandular hairs, no curved hairs. Inflorescence a lax raceme.
- Leaves: Opposite (alternate in inflorescence), short-stalked. Blade narrowly ovate–elliptic, with tapered base, roundish tips, rarely small-toothed, light green, occasionally reddish.
- Fruit: Tubular, 4-valved, glabrous, 3–6 cm (1.2–2.4 in.) long capsule. Plumed seeds oblanceolate.
- Habitat: Young, dense broadleaved willow forests, damp meadows, swamps, broad-leaved forests, springs, pond shores, stream banks, ditches, scree beds around the tree line and lower fell tundra.
- Flowering time: July–August.
Willowherb family has received new members even very recently when a precise taxonomic study demonstrated that what had been traditionally viewed as one species was in fact two. There has been a dispute over the species from the other angle too: milkflower willowherb has been tried to unite with its close lookalike, Hornemann’s willowherb (E. hornemannii). Milkflower willowherb’s position as a distinct species is not however under threat. Compared to Hornemann’s willowherb its leaves are thinner, more densely serrated, and a lighter shade of green and the flowers are smaller, often also quite white. Both species’ subterraneous runners are short, but Hornemann’s willowherb’s stand out more clearly. Without doubt they are close relatives, but the species can also be confused with several other Lapland willowherbs, especially chickweed willowherb (E. alsinifolium) and pimpernel willowherb (E. anagallidifolium), which can look the same at first glance.
Milkflower willowherb is one of Finland’s half-dozen northern willowherb species which are completely lacking from southern Finland: the species’ southernmost stands are on Pallastunturi Fell. Milkflower willowherb cannot actually be described as common north of the Arctic Circle: it is rare on Enontekiö Fell and rarer still on Salla and Utsjoki Fells. Many Finnish willowherb species prefer a damp habitat but milkflower willowherb grows on quite dry ground and actually prefers sunny slopes. It occasionally grows in large stands, but they are usually rather sparse, so the species must be looked for among other flora. The most promising places to look are usually mountain birch and broad-leaf woodlands, stream banks, large meadows and gravels on the edge of forests or in the lower tundra regions.