2. Tanacetum parthenium (L.) Sch. Bip. (feverfew)

Chrysanthemum parthenium L.

Pl. 228 c, d; Map 956

Plants taprooted, not producing rhizomes. Stems 30–80 cm long, glabrous toward the base, minutely hairy toward the tip. Leaves 1–8(–12) cm long, the basal leaves usually absent by flowering time, short-petiolate to sessile (the basal leaves long-petiolate). Leaf blades pinnately compound, less commonly the uppermost only deeply lobed, ovate to elliptic in outline, the primary leaflets (or lobes) mostly 3 or 5, these deeply pinnately or ternately lobed, oblanceolate to elliptic in outline, rounded to bluntly pointed at the tip, angled or short-tapered at the base, the margins otherwise sharply toothed, both surfaces moderately to densely glandular and sparsely to moderately pubescent with fine, curly hairs. Heads conspicuously radiate. Involucre 2.5–4.0 mm long, broadly and shallowly cup-shaped, the bracts in 2–4 series, the main body narrowly lanceolate to lanceolate or oblong-lanceolate, narrowed to a sharply pointed tip, the margins with a narrow, thin, papery border, the outer surface glandular and somewhat cobwebby-hairy, at least toward the margins. Ray florets 10–21, the corolla 4–8 mm long, white. Disc florets with the corollas 1.5–2.2 mm long. Pappus a short collar or crown, sometimes absent. Fruits 1.3–1.8 mm long, usually fairly strongly 7–10-ribbed. 2n=18. June–September.

Introduced, uncommon and widely scattered (native of Europe, Asia, introduced widely in North America). Open, disturbed areas.

Feverfew produces an essential oil that is used medicinally as an anti-inflammatory agent and analgesic and also as a natural insect repellant. The oil also sometimes is used in combination with other ingredients in aromatherapy. Side effects that have been reported include decreased blood clotting, swelling of the mouth, and stomachache, especially if the leaves are chewed.