1. Buchnera americana L. (blue hearts)

Pl. 470 d–f; Map 2155

Plants annual, hemiparasitic, dark green, sometimes purplish-tinged, sometimes blackening upon drying. Stems 30–90 cm long, solitary or few, usually unbranched, erect or strongly ascending, circular to bluntly 4-angled, moderately to densely pubescent with short, stiff, upward-angled, nonglandular, pustular-based hairs, roughened to the touch. Leaves opposite, sessile. Leaf blades 2–6(–10) cm long, lanceolate to broadly ovate, unlobed, the margins coarsely few-toothed, the surfaces moderately to densely pubescent with short, stiff, upward-angled, nonglandular, pustular-based hairs, roughened to the touch. Inflorescences open to moderately dense, terminal spikes with small bracts shorter than the calyces, these lanceolate to narrowly ovate, unlobed, roughened-hairy, the flowers paired at the nodes or subopposite, stalkless; bractlets 2 per flower, shorter than the bracts, linear to narrowly lanceolate. Cleistogamous flowers absent. Calyces 6–9 mm long, tubular at flowering, becoming distended and somewhat urn-shaped at fruiting, moderately roughened-hairy on the outer surface, 5-lobed, actinomorphic, the lobes much shorter than the tube, triangular. Corollas 15–23 mm long, 5-lobed, weakly zygomorphic, trumpet-shaped, deep or dark purple to bluish purple, the tube hairy on the inner surface, roughened-hairy on the outer surface, the throat densely hairy, the lobes shorter than the tube, abruptly spreading, their outer surface hairy, especially toward the base, the inner surface glabrous or sparsely hairy, the margins glabrous. Stamens with the filaments of 2 lengths, short, not exserted, the anthers appearing to have only 1 sac, narrowly lanceolate, yellow, glabrous. Style relatively short and stout, not exserted, the stigma club-shaped, unlobed. Fruits 6–8 mm long, asymmetrically oblong-ovoid (appearing somewhat pouched on 1 side at the base), usually slightly flattened, glabrous. Seeds 0.6–0.8 mm long, angular, irregularly oblong-ellipsoid to oblong-obconic, the surface with a fine network of low ridges and narrow, elongate areolae, brown to dark brown. 2n=42. June–September.

Scattered south of the Missouri River, but absent from the Mississippi Lowlands Division (eastern U.S. west to Illinois, Kansas, and Texas; Canada, Mexico). Upland prairies, glades, and savannas; occasionally also old fields and roadsides.

Pennell (1935) suggested that although the slender tube of Buchnera flowers appeared to be an adaptation for butterfly pollination, the interior pubescence and short staminal filaments likely resulted in significant amounts of self-pollination.