2. Matricaria discoidea DC. (pineapple weed)

M. matricarioides, misapplied

Chamomilla suaveolens (Pursh) Rydb.

Pl. 227 f, g; Map 954

Plants aromatic, with an often strong odor of pineapple when bruised or crushed. Stems 4–30 cm tall, glabrous or nearly so. Leaf blades 1–3(–7) cm long, elliptic to oblong-obovate in outline, mostly deeply 2 times pinnately lobed, the basal primary lobes usually well spaced and not appearing clustered, the ultimate lobes 2–10 mm long, linear to threadlike, 1-veined. Heads discoid, the stalks 0.3–1.2 cm long, relatively stout. Involucre 2.5–4.0 mm long. Disc florets with the corolla 1.0–1.5 mm long, mostly 4-lobed, greenish yellow. Pappus absent or a minute collar (to 0.1 mm long). Fruits 0.9–1.2 mm long, 3–5-ribbed, the ribs often relatively small. 2n=18. May–October.

Introduced, scattered nearly throughout the state (native of the western U.S.; introduced nearly worldwide). Fallow fields, pastures, barnyards, railroads, roadsides, and open, disturbed areas.

This species was used by Native Americans for its medicinal and aromatic properties (Moerman, 1998). The limits of its native range have been obscured by its widespread weediness. Steyermark (1963) noted that it was well established in the St. Louis area by 1825 and that George Engelmann mistakenly considered it native to Missouri. It appears to have become much more abundant, particularly in the southern half of the state, since Steyermark’s (1963) treatment.

Matricaria discoidea formerly was widely known as M. matricarioides (Less.) Porter (Steyermark, 1963; Gleason and Cronquist, 1991). However, that name is a taxonomic synonym of Tanacetum huronense Nutt., a different species that occurs only to the north of Missouri (Gandhi and Thomas, 1991).