1. Dipsacus fullonum L. (common teasel, wild teasel)

D. sylvestris Huds.

Pl. 373 b–d; Map 1632

Stems 0.4–2.5 m long. Basal leaves simple, oblong-oblanceolate, the margins scalloped to bluntly toothed and often also prickly. Stem leaves 3–35 cm long, sessile at each node or sometimes inconspicuously fused only at the very base, usually somewhat folded longitudinally, the lowermost oblanceolate to lanceolate, the margins scalloped to bluntly toothed and often also prickly, the uppermost linear, the margins usually entire. Involucral bracts at flowering 2–15 cm long, the longest usually longer than the head, narrowly linear, appearing angled or somewhat flattened in cross-section. Heads 3–10 cm long, ovoid to cylindrical-ovoid. Calyces 0.9–1.2 mm long. Corollas 10–15 mm long, the tube white, the lobes lavender, rarely white. Stamens with the anthers lavender, rarely white. Fruits (including the involucel but not the calyx) 3–5 mm long, linear, the involucel 4-angled, 8-ribbed, brown to dark brown. 2n=16, 18. June–October.

Introduced, scattered nearly throughout the state, but apparently absent from the Mississippi Lowlands Division and most of the Glaciated Plains (native of Europe; widely naturalized in the U.S. and Canada). Banks of streams; more commonly roadsides, railroads, pastures, old fields, fallow fields, fencerows, and open or brushy disturbed areas.

Dipsacus fullonum has been established in Missouri for a relatively long time and was collected in widespread counties such as Greene, Cole, and St. Louis prior to 1880. In recent years, it appears to have declined in the state, perhaps because of competition from the more robust and aggressive D. laciniatus. Before Ferguson and Brizicky (1965) clarified the nomenclature of the D. fullonum complex, there was considerable confusion in the botanical literature over the proper application of names to the weedy wild plant now known as D. fullonum and its cultivated relative, D. sativus. Rare white-flowered plants have been called D. sylvestris f. albidus Steyerm. and were first reported for Missouri by Dunn (1982).