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Winged loosestrife is a native species that has a central stem up to 3' tall, much more modest that its notorious cousin, purple loosestrife. The stem is four-sided, narrowly winged, and largely hairless; wings run along the stem but are interrupted at the leaf nodes. The inflorescence is a spike up to 1.5' long; the flowers develop singly or in pairs from the axils of bracts on the inflorescence. Each flower is pale lavender or purple and smaller than the flowers of purple loosestrife (1/4-1/2") but otherwise superficially similar — pale purple or lavender, six wrinkled petals with a medial purple stripe, six stamens. The light green, narrow calyx is about as long as the petals, has six (not five) lance-shaped teeth, and bold longitudinal stripes. The style may or may not protrude from the corolla — the flowers are distylous so the styles may either lie just inside the flower throat or protrude well outside; the style has a fuzzy, green, globular stigma. The fruit is a capsule that develops in the remnants of the calyx. Winged loosestrife prefers wet soils and is a less showy plant than purple loosestrife, but it is a native plant that plays nicely with its neighbors.

Lythrum

Lythrum alatum

winged loosestrife [Blooms: Jun-Aug]

Purple loosestrife plants are 2-5' tall. The stems branch frequently, are square in section or ridged, and are very hairy except where the stem is woody. The very showy flower spikes can be up to 20" long. Individual flowers are 1/2-1" wide that are sessile or on very short stalks; there are 5-7 (usually six) purple, wrinkled petals with a dark purple line near their base. (Imagine purple crepe paper.) The long tubular calyx is yellow-green, ridged, and hairy, with five long, narrow teeth at the distal end. Purple loosestrife is "tristylous" — it exhibits three discrete flower morphs that differ in the relative lengths of the stamens and style. Each plant bears flowers of only a single morph. Each morph has two different lengths of stamens — pistil short, stamens long AND stamens intermediate in length; pistil intermediate in length, stamens short AND long; and pistil long, stamens short AND intermediate in length. Tristyly presumably minimizes self-fertilization. Purple loosestrife is a very aggressive, invasive species which crowds out other species. Another invasive which is also called purple loosestrife, Lythrum virgatum, has similar flowers but the leaves narrow towards their base. (L. virgatum is not known to occur — yet — in Illinois.) Do not confuse purple loosestrife with the native winged loosestrife (Lythrum alatum) which has winged stems, smaller flowers (1/2"), hairless foliage, and solitary flowers in leaf axils. It's not as striking a plant as purple loosestrife, but it plays better with its neighbors.

Lythrum

Lythrum salicaria

purple loosestrife [Blooms: Jun-Sep]