1. Lythrum alatum Pursh, Fl. Amer. Sept. 1: 334. 1813.
[E F W]
Blue waxweed, winged loosestrife
Herbs perennial, or subshrubs, slender or robust, 5–15 dm, green or slightly gray glaucous, glabrous. Stems erect, much-branched distally. Leaves opposite to subopposite proximally, alternate distally, branch leaves gradually smaller than those on main stem; sessile; blade ovate to oblong and base subcordate to rounded, or lanceolate to linear-lanceolate and base attenuate, 10–76 × 2–14 mm. Inflorescences racemes. Flowers alternate, subsessile, pedicel stout, distylous; floral tube cylindrical, 3–7 mm × 1 mm; epicalyx segments 2 times length of sepals; petals purple, obovate or oblong, 2–6.5 × 1.5–3 mm; nectary encircling base of ovary; stamens 6. Capsules septicidal or septifragal. Seeds ca. 30, obovoid to fusiform.
Varieties 2 (2 in the flora): North America; introduced in Mexico, West Indies.
Taxonomic judgement has varied as to limits of Lythrum alatum and closely related taxa centered around it (L. californicum, L. flagellare, and L. ovalifolium). Identification of species from sympatric areas is often difficult and morphology suggests that hybridization occurs where ranges overlap. Lythrum californicum apparently hybridizes with L. alatum var. alatum in Kansas and Oklahoma, and with L. alatum var. lanceolatum in Oklahoma and eastern Texas. Variety lanceolatum may also hybridize with L. curtissiiin Calhoun County, Georgia, where they co-occur. A specimen combining features of L. alatum and L. flagellare is known from Hernando County, Florida.