1.
Machaeranthera tanacetifolia
(Kunth) Nees, Gen. Sp. Aster. 225. 1832.
Tansy-aster, tansyleaf aster , tahoka-daisy
Aster tanacetifolius
Kunth in A. von Humboldt et al., Nov. Gen. Sp. 4(fol.): 74. 1818; 4(qto.): 95. 1820
Annuals or biennials,
5—100 cm.
Leaves
8—110 × 4—40 mm.
Involucres
hemispheric, 6—11 mm.
Phyllaries
(24—)40—80(—100) in 3—6 series, linear-lanceolate to linear, 4—11 × 0.5—1.2 mm, apices usually spreading to reflexed, sometimes appressed, long-acuminate.
Receptacles
flat to convex, 3.5—8(—10) mm diam.
Ray florets
12—40(—50); laminae 8—20 × 1—3.5 mm.
Disc florets
(18—)40—160; corollas 4—7 mm, glabrous or glabrate; lobes 0.3—0.7(—1) mm, glabrous.
Cypselae
2—3.5(—4) mm;
pappi
2—8 mm.
2
n
= 8.
Flowering Mar—Oct. Grasslands,
Larrea-
dominated desert scrub, pine-oak and pinyon-juniper woodlands, streambeds, roadsides, disturbed areas; 800—2500 m; Alta.; Ariz., Calif., Colo., Kans., Mont., Nebr., Nev., N.Mex., Okla., S.Dak., Tex., Utah, Wyo.; Mexico (Aguascalientes, Chihuahua, Coahuila, Durango, Nuevo León, San Luis Potosí, Zacatecas).
Machaeranthera tanacetifolia
is present in the southern Rocky Mountains, western Great Plains, and southwestern desert regions. It has also been reported from Illinois and New York, but in both cases is most likely introduced. Because of its large showy heads,
M. tanacetifolia
is sometimes planted as an ornamental.
