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Published In: Memoirs of the Torrey Botanical Club 5(20): 311. 1894. (Mem. Torrey Bot. Club) Name publication detailView in BotanicusView in Biodiversity Heritage Library

Project Name Data (Last Modified On 8/11/2017)
Acceptance : Accepted
Project Data     (Last Modified On 7/9/2009)
Status: Native


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2. Eupatorium capillifolium (Lam.) Small (dog fennel)

Pl. 266 e, f; Map 1110

Stems 50–250 cm long, not hollow, moderately to densely short-hairy above the often nearly glabrous basal portion, green to yellowish green, sometimes purplish-tinged or brownish-mottled, occasionally slightly glaucous, the nodes often with small fascicles of axillary leaves less than 1/2 as long as the main stem leaves. Leaves mostly opposite, those of the uppermost nodes sometimes alternate, sessile or with short petioles 1–10 mm long. Leaf blades 2–10 cm long, mostly 1–3 times pinnately or ternately deeply and irregularly lobed or dissected into relatively few long, threadlike segments (the uppermost merely simple and threadlike), these 0.2–0.5(–1.0) mm wide, the margins more or less entire, sometimes rolled under, the surfaces glabrous but sparsely to densely gland-dotted, with 1 main vein. Inflorescences axillary clusters, these appearing as elongate terminal panicles with racemose branches. Involucre 2.0–3.5 mm long, more or less cup-shaped to nearly cylindrical (sometimes bell-shaped after pressing), the bracts linear to narrowly lanceolate or narrowly oblong, sharply pointed at the tip, the narrow margins thin and pale (sometimes only toward the base), faintly 1- or 3-nerved, glabrous, light green, sometimes purplish-tinged toward the tip. Disc florets 3–6. Corollas 2.0–2.5 mm long, the surface often inconspicuously glandular, white, greenish white, or pale cream-colored. Fruits 1.0–1.5 mm long. 2n=20. August–October.

Introduced, uncommon, known thus far only from St. Louis City and County (native from New Jersey to Florida west to Texas; introduced farther north and west). Railroads, gardens, and open, disturbed areas.

Eupatorium capillifolium was first reported by Steyermark (1963) in the supplement to his Flora of Missouri, based on collections made by Viktor Mühlenbach in the St. Louis railyards. In parts of the southeastern United States, the species is a problem weed in pastures. Apparently it contains low levels of the toxin tremetol (see the treatment of Ageratina for further discussion), which can cause dehydration and other symptoms in livestock that ingest the plants in quantity.



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