Tansy
Tansy (Tanacetum vulgare) is a perennial herbaceous flowering plant in the aster family (Asteraceae), native to temperate regions of Europe and western Asia, featuring fern-like aromatic leaves divided into numerous narrow segments and dense clusters of small, yellow, button-like flower heads borne on upright stems up to 1.5 meters tall.[1][2]
Introduced to North America for ornamental and medicinal purposes, tansy has naturalized aggressively and is classified as invasive in many areas, forming dense monocultures via rhizomes and prolific seed production exceeding 50,000 seeds per plant annually, thereby outcompeting native vegetation, reducing forage for livestock, and altering local ecosystems by restricting water flow in riparian zones.[3][4][5]
Historically employed in folk medicine as a vermifuge for intestinal parasites, emmenagogue, and antispasmodic, tansy contains the toxic monoterpene ketone thujone, which renders it hazardous for internal use, with no established role in contemporary herbal practice due to risks of convulsions, organ damage, and abortion; livestock poisonings occur rarely but are documented when consumed in large quantities, while humans and sensitive animals like horses and cattle face greater vulnerability.[6][7][2]
Beyond toxicity concerns, tansy's strong aroma provides insect-repellent properties effective against arthropods, and it has been utilized in traditional brewing to flavor beer prior to hops dominance, though regulatory limits now restrict its thujone content in such applications.[7][6]
Taxonomy and Description
Botanical Characteristics
Tanacetum vulgare, commonly known as tansy, is a perennial herbaceous plant in the Asteraceae family.[1] It grows as an erect forb typically reaching heights of 50 to 150 cm, though some specimens may attain up to 200 cm under favorable conditions.[8] The plant arises from a branched rhizome system that facilitates vegetative propagation and patch-forming growth.[9] Stems are solitary or clustered, generally smooth and glabrous, often exhibiting a reddish tint, and branch extensively near the apex to support the inflorescence.[8] Leaves are alternate, pinnately compound, and deeply lobed or divided into narrow, lanceolate segments resembling fern fronds, measuring 10-20 cm in length; they emit a strong aromatic odor when crushed.[1] The foliage is deep green and glabrous or sparsely hairy.[10] Flowers form in late June to September, arranged in dense, flat-topped corymbs of numerous small, button-like capitula, each 6-12 mm across with bright yellow rayless florets.[11] Each floret head consists of 20-60 tubular disk florets surrounded by a campanulate involucre.[8] The plant produces abundant achenes, small dry fruits measuring 1-1.8 mm long, crowned by a minute pappus or absent in some cases; seeds primarily disperse short distances via wind, gravity, or water, though long-distance spread occurs via attachment to animals or human activity.[8][11]