Tanacetum bipinnatum

Perennials, 5-30(-80) cm. Stems (sometimes purple-tinged) 1-2+, ± decumbent to ascending or erect, branched. Leaves basal (soon withering) and cauline; petiolate (bases often clasping) or sessile; blades ± ovate or elliptic to obovate or spatulate, mostly 7-25+ × 3-5(-10+) cm, 2-3-pinnately lobed (primary lobes mostly 6-24+ pairs, narrowly oblong to linear-elliptic or linear, lobules oblong or ovate to ± lanceolate, sometimes curled), ultimate margins entire or ± dentate, faces usually ± villous or arachno-villous to lanate, sometimes glabrescent or glabrate, usually gland-dotted (in pits). Heads (2-)5-12(-20+) in corymbiform arrays or borne singly. Involucres 8-22+ mm diam. Receptacles flat to hemispheric. Ray florets 8-21+ (pistillate, fertile; corollas pale yellow to yellow, laminae mostly 1-7+ mm, usually 3-lobed) or 0 (heads quasi-radiant or -radiate or ± disciform, peripheral pistillate florets 15-30+; corollas pale yellow, ± zygomorphic, lobes 3-5, abaxial more pronounced). Disc corollas (2-)3(-4) mm. Cypselae 2-3(-4) mm, weakly 5-ribbed or -angled, gland-dotted; pappi coroniform, 0.1-0.5+ mm (entire or erose to lacerate). 2n = 54.

Flowering May-Sep. Dunes, other sandy sites, calcareous soils, coastal scrub; 0-200+ m; Alta., B.C., Man., N.B., Nfld. and Labr. (Nfld.), Ont., Que., Sask., Yukon; Alaska, Calif., Maine, Mich., Oreg, Wash., Wis.; Eurasia.

The circumscription of Tanacetum bipinnatum adopted here includes not only T. huronense (see E. Hultén 1941-1950, vol. 10, 1968) but T. camphoratum and T. douglasii as well (see D. W. Kyhos and P. H. Raven 1982; C. J. Mickelson and H. H. Iltis 1966). Subspecies bipinnatum has been distinguished from subsp. huronense by having heads borne singly or 2-4 together versus (1-)3-12(-20+) in corymbiform arrays, phyllary margins dark brown versus pale brown, and laminae of ray corollas mostly 3-7 mm versus 1-3 mm. Relatively low plants, 10-20(-40 cm) from dune habitats along the southern shore of Lake Athabasca, Saskatchewan, with mostly 1-4, lanate cauline leaves and 1(-2) heads per flowering stem have been called T. huronense var. floccosum.