22. Chenopodium watsonii A. Nelson

Pl. 356 h, i; Map 1542

Plants annual, with a pronounced unpleasant odor. Stems 2–15(–30) cm long, spreading to more commonly erect or ascending, bushy, usually much-branched from the base, sparsely to densely white-mealy, sometimes appearing striped. Leaves mostly long-petiolate. Leaf blades 1–4 cm long, mostly 1.0–1.5 times as long as wide (mostly 6–20 mm wide), ovate to broadly ovate or rhombic, rounded or bluntly pointed at the tip, angled or tapered at the base, with 1 or rarely 2 pairs of triangular lobes below the midpoint, green to yellowish green, thick and leathery in texture, the margins otherwise entire or rarely shallowly few-toothed, the upper surface sparsely to moderately white-mealy, the undersurface densely white-mealy. Venation noticeably branched, with 1 or 3 main veins. Inflorescences axillary and terminal, consisting of clusters or short spikes with dense clusters of flowers, the terminal spikes usually grouped into small panicles. Flowers not all maturing at the same time. Calyx 5-lobed to below the midpoint, covering the entire fruit except sometimes for a minute area surrounding the style, the lobes 0.7–1.0 mm long, ovate to oblong-ovate, mostly bluntly pointed at the tip, strongly keeled dorsally, moderately to densely white-mealy. Stamens 5. Stigmas 2. Fruits 0.9–1.2 mm wide, depressed-ovoid, the seeds positioned horizontally, the wall relatively thick, papery and opaque–white at maturity, finely roughened at maturity, difficult to separate from the seed. Seeds black, shiny, wrinkled, bluntly angled along the rim. 2n=18. June–September.

Introduced, uncommon, known only from the city of St. Louis (Arizona to Montana east to South Dakota and Kansas; Canada; introduced in Missouri and Maine). Railroads.

This species was first reported from Missouri by Mühlenbach (1979).