1. Lobularia maritima (L.) Desv. (sweet alyssum)

Alyssum maritimum L.

Pl. 324 a, b; Map 1370

Plants perennial herbs, terrestrial, usually appearing grayish-tinged, uniformly pubescent with appressed hairs, each hair sessile and with 2 opposite branches, thus appearing as a straight line. Stems (5–)12–24(–40) cm long, spreading to ascending, branched. Leaves alternate, (1–)2–5 cm long, sessile or short-petiolate, not clasping, the blades linear to narrowly oblanceolate, the margins entire. Inflorescences racemes or few-branched panicles, the lower branches subtended by reduced leaves. Sepals 1.5–2.0(–2.4) mm long, ascending, oblong to ovate. Petals 2–4 mm long, not lobed, white to purple. Styles 0.5–1.0 mm long. Fruits spreading, (2.0–)2.5–3.5(–4.2) mm long, about as long as wide or less than 2 times as long as wide, elliptic in outline, somewhat flattened parallel to the septum, each valve with an obscure midnerve, sparsely hairy, dehiscing longitudinally. Seeds 1 per locule, 1.0–1.5(–2.0) mm long, circular to broadly elliptic in outline, flattened, the margin wingless or narrowly winged, the surface with minute papillae, orange. 2n=24. April–October.

Introduced, known thus far only from the city of St. Louis (native of the western Mediterranean region, cultivated worldwide, and widely introduced in North America). Railroads and disturbed areas.

This species is perhaps the most widely cultivated of the ornamental crucifers (Al-Shehbaz, 1987), and its small, white to purple flowers are quite fragrant. It has escaped from cultivation and become naturalized at a number of sites in the eastern United States, and it is to be expected elsewhere in Missouri.