Clammy cuphea, blue waxweed

Lythrum petiolatum Linnaeus 1753, not Cuphea petiolata Pohl ex Koehne 1877; Parsonsia petiolata (Linnaeus) Rusby

Herbs annual, 1–6 dm, with fibrous roots. Stems erect to de­cum­bent, often reddish, much-branched, purple-red glandular-setose, glandular-viscid. Leaves opposite, petiolate; petiole (2–)5–15(–20) mm; blade narrowly lanceolate to narrowly ovate, 20–50 × 6–20 mm, base attenuate. Racemes leafy. Pedicels 1–5 mm. Flowers alternate, solitary, interpetiolar, sometimes with 1 axillary; floral tube pale abaxially, deep purple-red adaxially, 8–12 × 1–2 mm, purple-red glandular-setose; base rounded or a descending spur, 0.5–1 mm; inner surface glabrous proximally, densely villous distal to stamens; epicalyx segments thick, 2 flanking the adaxialmost sepal terminated by a bristle; sepals unequal, adaxialmost longer; petals 6, purple, oblanceolate, unequal, 4 abaxial petals 2–5 × 0.4–0.6 mm, 2 upper petals 3–6 × 1.5–2.5 mm; stamens (5–)11, reaching or surpassing sinus of sepals. Seeds 7–10, oblong-elliptic in outline, 2.3–2.8 × 1.8–2.3 mm, margin rounded. 2n = 12.

Flowering summer–fall. Weedy in pastures, road­sides, ditches, grassy borders, disturbed moist woods along trails; 0–900 m; Ont.; Ala., Ark., Conn., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Md., Mass., Miss., Mo., Nebr., N.H., N.J., N.Y., N.C., Ohio, Okla., Pa., S.C., Tenn., Tex., Vt., Va., W.Va.

Cuphea viscosissima of the eastern and central United States is the most common and widespread species of Cuphea in the flora area; it is naturalized in Ontario. It is closely related to C. lanceolata W. T. Aiton of eastern and central Mexico, with which it shares the lowest known chromosome number in the genus, 2n = 12. The stamen number is typically 11, but varies in some populations (W. H. Duncan 1950).

Cuphea petiolata (Linnaeus) Koehne is an illegitimate name that pertains here.