Annual, biennial or perennial branched herbs, with leafy stems, alternate, mostly serrate or pinnatifid leaves, the teeth or lobes usually bristle-tipped, and large heads of both tubular and radiate flowers. Involucre of numerous series of imbricated canescent or glandular bracts with herbaceous or foliaceous spreading or appressed tips. Receptacle alveolate, the alveoli usually toothed or lacerate. Ray-flowers numerous, violet to red or purple, pistillate. Disk-flowers perfect, their corollas tubular, 5-lobed, yellow, changing to red or brown; anthers exserted, appendaged at the tip, rounded at the base; style-appendages subulate to lanceolate. Achenes turbinate, narrowed below, pubescent. Pappus of numrous stiff, rough unequal bristles. [Greek, sickle-anther.]

About 15 species, natives of western North America. Type species: Machaeranthera anaceti-folia (H.B.K.) Nees. Annual or biennial; leaves pinnatifid.

1. M. tanacetifolia.

Perennial or biennial; leaves sharply serrate.

2. M. sessiliflora.

1. Machaeranthera Tanacetifolia (H.B.K.) Nees. Tansy Aster. Dagger-Flower

Fig. 4359

Aster tanacetifolius H.B.K. Nov. Gen. Sp. 4: 95. 1820.

M. tanacetifolia Nees, Gen. & Sp. Ast. 225. 1832.

Annual or biennial; stem glandular-pubescent, often viscid, densely leafy, much branched and bushy, 1°-2° high. Leaves sessile or short-petioled, pubescent, the lowest 1-3' long, 2-3-pinnatifid, their lobes linear or oblong, acute or mucronate, the upper pinnatifid, those of the branches sometimes entire; heads numerous, corymbose-paniculate, l'-2' broad; involucre hemispheric, 4"-6" high, its bracts linear, glandular, imbricated in 5-7 series, their green tips very squarrose; rays 15-25, violet-purple, 5"-8" long, pappus copious, tawny; achenes villous.

In dry soil, South Dakota to Nebraska, Texas, Mexico, Montana and California. June-Aug.

2. Machaeranthera Sessiliflora (Nutt.) Greene. Viscid Aster

Fig. 4360

Dieteria sessiliflora Nutt. Trans. Am. Phil. Soc. 7: 301. 1840.

M. sessiliflora Greene, Pittonia 3: 60. 1896.

Stem usually stout, finely rough-pubescent or canescent, branched, and viscid-glandular above, 1°-2° high. Leaves lanceolate, linear, or the lowest spatulate, sessile, somewhat viscid, sharply incised-dentate, the larger 1'-3' long, the teeth bristle-tipped; heads numerous, racemose, or corymbose above, 1'-1 1/2' broad, the lower often nearly sessile; involucre broadly turbinate or hemispheric, 4"-6" high, its bracts acute, imbricated in 6-10 series, their tips strongly squarrose; rays numerous, violet, 4"-6" long; pappus copious; achenes narrow, appressed-pubescent.

In dry soil, central and western Nebraska and Colorado. July-Oct.

A Kansas plant differs from this species by having acute appressed tips to the involucral bracts.