1. Datura L. (jimsonweed, thorn apple)

Plants annual or perennial herbs, sometimes with a somewhat thickened or woody rootstock, unarmed (except for the prickly fruits). Stems erect to loosely ascending from a spreading base, relatively stout, with few to several ascending to spreading branches (sometimes appearing equally forked or with whorls of 3 branches), sometimes mostly toward the tip, glabrous or more commonly short-hairy. Leaves alternate, but those near the stem tip sometimes appearing opposite, moderately to long-petiolate. Leaf blades simple, unlobed or irregularly pinnately lobed, the margins otherwise wavy or coarsely toothed, the surfaces usually hairy. Inflorescences initially terminal, of solitary flowers, but later appearing produced in the axils of forked or 3-branched nodes. Flowers erect or ascending, the fruits sometimes nodding or pendant. Calyces 3.5–10.0 cm long, shallowly and unequally 5-lobed at the tip, narrowly tubular at flowering, rounded to more or less truncate at the base, lacking basal auricles, the sides rounded or 5-angled to narrowly winged, with a circumscissile zone of abscission toward the base, the apical portion shed after flowering, leaving a small, persistent, circular disc at the base of the fruit, this strongly reflexed in our species (more or less flat elsewhere). Corollas 6–20 cm long, funnelform at full flowering (appearing tubular at other times), very shallowly 5- or 10-lobed, the lobes toothlike, abruptly tapered to often slender, sharply pointed tips, usually appearing spirally twisted and pleated in bud, white, sometimes purplish-tinged or pale to light purple. Stamens with relatively long filaments, the anthers free, erect, positioned in a loose ring, not exserted, dehiscent longitudinally, light yellow to nearly white, usually hairy. Ovary 2-carpellate but appearing 4-locular, the style elongate, positioned at about the level of the anthers, green. Fruits capsules, dry, globose to broadly oblong-ovoid, 4-locular, pale green at maturity, becoming tan with age, dehiscent longitudinally from the tip (sometimes irregularly so), with numerous seeds, the surface armed (unarmed elsewhere) with dense prickles, these slender above the expanded base, straight. Seeds 3–6 mm in longest dimension, more or less kidney-shaped to asymmetrically ovate, flattened, the surface smooth, minutely pitted or finely wrinkled, sometimes only faintly so, more or less shiny, variously colored, lacking wings, the dorsal margin sometimes bordered by a pair of parallel grooves. Eight to 11 species, North America, introduced widely.

Plants of Datura are highly toxic to humans and other mammals, and contain principal alkaloids similar to those of Atropa (belladonna) and related genera (Burrows and Tyrl, 2001). The species have long been used medicinally (in small dosage) to treat asthma and for their narcotic properties, among other maladies. The genus is important as a ceremonial hallucinogen for a number of North American Indian tribes (Moerman, 1998). However, euphoria-seeking amateurs who have ingested Datura intending to reproduce the drug effects ascribed to the plants have fairly frequently become poisoned instead, leading to seizures, coma, and sometimes death.

The flowers of Datura species, which are pale-colored, night-flowering, fragrant, and long-tubed, are adapted to pollination by long-tongued nocturnal hawk moths (H. G. Baker, 1961; V. Grant and K. Grant, 1983). However, although the flowers of D. stramonium are visited by both hawkmoths and bees, apparently they are mostly self-pollinated (Motten and Antonovics, 1992).

Some authors have accepted an expanded circumscription of Datura to include five to seven additional arborescent, South American species (Hammer et al., 1983), but molecular studies have confirmed that this lineage should be treated in the segregate genus Brugmansia Pers. (Mace et al., 1999). Members of this genus also produce showy, often fragrant flowers with large, funnelform corollas, but the flowers are pendant and in some species the corollas are yellow, pink, or orange toward the tip. Some species of Brugmansia and their hybrids also are cultivated as ornamentals, but none of these can overwinter outdoors in Missouri.