1. Ruta graveolens L. (common rue)

Pl. 552 f, g; Map 2564

Plants perennial herbs (shrubs elsewhere), 0.3–1.0 m tall. Stems with ascending branches, unarmed, glabrous. Leaves alternate, the lowermost usually long-petiolate, the petioles progressively shorter to the stem tip, the uppermost leaves often sessile, the petiole not jointed at the tip, unwinged. Leaf blades 2–12 cm long, pinnately compound or deeply lobed, the leaflets or primary segments on all but the uppermost leaves again deeply pinnately lobed, the ultimate segments 0.3–1.5 cm long, oblanceolate to oblong-oblanceolate, mostly somewhat narrowed toward the base, rounded or broadly and bluntly pointed at the tip, the margins entire or minutely scalloped, the upper surface green to bluish green, glabrous, sometimes slightly glaucous, the undersurface similar but often slightly lighter green. Inflorescences terminal, more or less flat-topped panicles, the individual flowers short- to long-stalked. Flowers perfect. Sepals 4 or 5, 1–3 mm long and ovate to narrowly ovate at flowering, persistent, becoming elongate to 4–5 mm, and narrowly triangular to lanceolate-triangular at fruiting, glabrous. Petals 4 or 5, 4–7 mm long, narrowly spatulate to narrowly oblong-obovate, overlapping in bud, narrowed to a stalklike basal portion, incurved and somewhat hooded toward the rounded tip, glabrous, greenish yellow to yellow. Stamens 8 or 10, in 2 unequal, alternating series, the filaments free, slender, slightly expanded toward the base, attached to a cushionlike, glabrous nectar disc below the slightly elevated ovary base. Ovary 4- or 5-locular, deeply 4- or 5-lobed from the tip, glabrous, each locule with usually numerous ovules, the slender style attached at the concave ovary tip, the stigma minute, more or less 4- or 5-lobed. Fruits capsules, 5–7 mm long, 6–8 mm wide, 4- or 5-lobed from the tip to about the midpoint, each or the blunt, hornlike lobes dehiscent along the inner suture from the tip to the fusion point, the outer surface leathery, slightly wrinkled and/or pitted, yellowish green, glabrous. Seeds few to several per locule, 1.3–2.0 mm long, more or less semicircular (asymmetrically elliptic) in outline, wedge-shaped to triangular in cross-section, the outer surface with dense, small tubercles, yellowish brown to dark brown or nearly black, somewhat shiny. 2n=72, 81. June–July.

Introduced, uncommon, sporadic (native of Europe; widely cultivated but introduced sporadically in the New World). Open disturbed areas.

The Missouri collections are historical and it is likely that the species does not persist long outside of cultivation. The common rue has a long history of use as a garden ornamental, spice, and medicinal plant. However, Brizicky (1962) noted that the volatile oil has unpleasant side effects (gastric inflammation) when ingested in sufficient quantity and that the species should be considered poisonous. He also noted that the foliage causes dermatitis in some individuals. Poutaraud et al. (2000) noted that among the array of secondary metabolites produced in this species are furanocoumarins, which induce photodermatitis. They investigated methods of cultivating and harvesting R. graveolens to maximize the yield of furanocoumarins, which are used in treating psoriasis and some types of skin cancers, as well as in the treatment of multiple sclerosis.