Lythrum alatum var. alatum

Native

Wet to moist. Prairies, meadows, shores, shallows. Full sun to partial shade.

July to September

Pinkish-purple with a purple midvein

1′ to 4′

This is a 1′ to 4′ tall, erect, perennial forb rising from a taproot with rhizomes.

The stems are 4-angled and hairless with wand-like, straight, slender, and erect branches. The stem angles are slightly winged, which gives this plant its common name.

The leaves are thick, rigid, hairless, and untoothed. They are attached to the stem without leaf stalks, and are longer than the length of stem between the leaf’s base and that of the next leaf on the stem (internode). The lower leaves, those below the branches, are up to 4″ long and 2″ wide, becoming smaller as they ascend the stem. They are lance-shaped to egg-shaped, broadest below the middle or near the base, and taper to the tip. The lowest of them are opposite, the rest alternate. The upper leaves, those on the branches, are alternate, crowded, much smaller and proportionately narrower.

The inflorescence is composed of usually solitary but sometimes paired flowers rising from most of the the upper leaf axils.

The flowers are ¼″ to ½″ wide. The 6 petals are pinkish-purple with a purple midvein. There are usually 6, always less than 10, stamens per flower.

The sepals are fused for most of their length with each other and the petals into a ⅛″ to ¼″ long, slender, hairless tube (hypanthium) with 12 narrow but sharp wings. The sepal lobes alternate with very narrow appendages that are twice as long as the sepal lobes.

The fruit is a capsule.

Purple loosestrife (Lythrum salicaria), an introduced, invasive plant, has stems that are usually hairy, especially near the top. The inflorescence is a dense, 6″ to 14″ long, spike-like cluster of numerous flowers at the end of the stem. The flowers are larger, ½ to 1″ across. There are always at least 10, usually 12, stamens.