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Published In: Species Plantarum 2: 843. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library
 

Project Name Data (Last Modified On 7/9/2009)
Acceptance : Accepted
Project Data     (Last Modified On 8/10/2009)

 

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7. Tanacetum L. (tansy)

Plants perennial herbs (annual elsewhere), sometimes with rhizomes, weakly to more commonly strongly aromatic, glabrous or sparsely to densely hairy. Stems erect or ascending, branched or unbranched, finely ridged. Leaves alternate and basal (basal leaves sometimes withered by flowering time), sessile or short- to long-petiolate, sometimes with slightly broadened, more or less clasping bases. Leaf blades unlobed and bluntly toothed or deeply 1–2 times pinnately compound (sometimes only deeply many-lobed) with the leaflets deeply lobed and the ultimate segments sharply toothed and/or lobed, sharply pointed at the tip, hairy and/or glandular to nearly glabrous, 1- to 5-veined. Inflorescences panicles at the stem tips, these flat-topped or dome-shaped, bractless or with a few reduced leaves toward the base. Heads radiate or appearing discoid. Involucre cup-shaped to broadly cup-shaped, the bracts more or less in 2–5 overlapping series, the outer ones somewhat shorter, oblong-lanceolate to narrowly elliptic, rounded to bluntly or sharply pointed at the tip, sparsely to moderately hairy, tan to brown, sometimes with a green or brown midvein or subapical area, the midrib sometimes keeled, the margins and often also the tip thin and papery, somewhat irregular. Receptacle flat to somewhat convex at flowering, not conspicuously elongating at fruiting, solid, naked. Ray florets (when present) 10–20 or rarely more, pistillate, persistent, becoming reflexed after flowering, white (sometimes yellow when marginal florets are pistillate, not markedly enlarged, and only slightly zygomorphic), sometimes pinkish-tinged. Disc florets perfect (the marginal ones sometimes pistillate), numerous, the corolla yellow, minutely glandular, the 5 lobes without resin canals, persistent, the tube often somewhat flattened toward the tip, becoming swollen at fruiting. Pappus absent or more commonly a very short collar or crown. Fruits oblong-obovoid to slightly wedge-shaped in profile, sharply 5-angled or nearly circular in cross-section, not flattened, truncate at the base, the tip often slightly obliquely truncate, strongly 5-ribbed to slightly 10-ribbed, the ribs slender, smooth, the surface otherwise sparsely glandular, tan to brown. About 160 species, North America, Europe, Asia, Africa, introduced widely.

The taxonomic circumscription of Tanacetum remains controversial, especially the inclusion of species formerly classified into the genus Chrysanthemum. The genus is quite heterogeneous morphologically. For example, as presently circumscribed, the genus contains a large number of species with white to pink ray florets that formerly were segregated in the genus Pyrethrum (Zinn) Rchb. f., whereas Tanacetum in the strict sense has been characterized variously as having discoid heads or radiate heads with yellow rays (Bremer and Humphries, 1993).

Several, including all of the escaped Missouri taxa, are cultivated as garden ornamentals. The genus also contains a number of species used medicinally. Heads of the eastern European ornamental species T. cineariifolium (Trev.) Sch. Bip. are the primary natural source of the group of monoterpenes called pyrethrins. These compounds are the active ingredient in some tick repellents and also have a long history of other uses in insecticides. Synthetic derivatives of pyrethrins are known as pyrethroids.

 

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1 1. Leaves simple, unlobed or the basal leaves rarely with a few deep, irregular basal lobes, the margins otherwise bluntly and regularly toothed ... 1. T. BALSAMITA

Tanacetum balsamita
2 1. Leaves pinnately compound or deeply pinnately lobed with several pairs of leaflets or lobes throughout the length of the blade

3 2. Leaf blades with the primary leaflets or lobes mostly 3 or 5, these further divided; heads radiate with conspicuous, white ray florets 48 mm long ... 2. T. PARTHENIUM

Tanacetum parthenium
4 2. Leaf blades with the primary leaflets or lobes 921, these further divided; heads discoid, the marginal florets sometimes pistillate and slightly zygomorphic, but yellow and not enlarged ... 3. T. VULGARE Tanacetum vulgare
 
 
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