1. Lythrum alatum Pursh (winged loosestrife)

Pl. 449 d, e; Map 2036

Plants glabrous, the stems and leaf undersurfaces sometimes somewhat glaucous, usually producing rhizomes. Stems 40–80(–150) cm long, ascending, wandlike, often narrowly winged, at least toward the tip, the wings interrupted and forming minute auricles at the nodes. Leaves mostly opposite, at least the uppermost leaves usually alternate, the lowermost leaves rarely in whorls of 3, sessile. Leaf blades 0.5–4.0 cm long, narrowly lanceolate to oblong-lanceolate or oblong-triangular, the upper leaves sometimes linear or narrowly elliptic, rounded to truncate or very shallowly cordate (rarely narrowed to tapered) at the base, bluntly to sharply pointed (rarely those of the lowermost leaves nearly rounded) at the tip. Inflorescences of axillary flowers at the upper and often also median nodes, the flowers solitary or less commonly paired, in well-developed plants sometimes taking on the appearance of leafy terminal spikes, mostly short-stalked, each subtended by a pair of small bracts. Petals 3–7 mm long, lavender to reddish purple. Stamens (4–)6, the anthers usually dark purple. Pistils with a nectary disc. Seeds 0.4–0.6 mm long. 2n=20. June–September.

Scattered nearly throughout the state (eastern [mostly northeastern] U.S. west to North Dakota, Wyoming, Colorado, and Oklahoma; Canada, Mexico, Caribbean Islands). Banks of streams, rivers, and spring branches, marshes, fens, bottomland prairies, and wet depressions of upland prairies and glades; also ditches, edges of crop fields, railroads, roadsides, and wet disturbed areas.

Graham (1975) discussed morphological variation across the range of L. alatum. Earlier botanists had recognized as many as four species in the complex. Graham concluded that only two reasonably discrete taxa could be separated, which she chose to recognize as varieties of L. alatum.