GENUS 34. 



THISTLE FAMILY. 



435 



34. MACHAERANTHERA Nees, Gen. & Sp. Ast. 224. 1832. 



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. i. M. tanacetifolia. 



Perennial or biennial ; leaves sharply serrate. 2. M. sessiliflora. 



i. 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, i-2 high. Leaves sessile or short-petioled, 

 pubescent, the lowest i'-3' long, 2-3-pinnatifid, their 

 lobes linear or oblong, acute or mucronate, the up- 

 per pinnatifid, those of the branches sometimes en- 

 tire; heads numerous, corymbose-paniculate, i'-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, Mex- 

 ico, 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 ca- 

 nescent, branched, and viscid-glandular above, i-2 

 high. Leaves lanceolate, linear, or the lowest spatu- 

 late, sessile, somewhat viscid, sharply incised-dentate, 

 the larger i'~3' long, the teeth bristle-tipped; heads 

 numerous, racemose, or corymbose above, i'-ii' 

 broad, the lower often nearly sessile ; involucre broad- 

 ly turbinate or hemispheric, 4" -6" high, its bracts 

 acute, imbricated in 6-10 series, their tips strongly 

 squarrose; rays numerous, violet, 4"-6" long; pap- 

 pus copious ; achenes narrow, appressed-pubescent. 



In dry soil, central and western Nebraska and Colo- 

 rado. July-Oct. 



A Kansas plant differs from this species by having 

 acute appressed tips to the involucral bracts. 



35. ERIGERON L. Sp. PI. 863. 1753. 



Branching or scapose herbs, with alternate or basal leaves, and corymbose, paniculate or 

 solitary, peduncled heads of both tubular and radiate (rarely all tubular) flowers. Involucre 

 hemispheric, cylindric or campanulate, its bracts narrow, nearly equal, mostly imbricated in 

 but i or 2 series. Receptacle nearly flat, usually naked. Ray-flowers, in our species, white, 

 violet or purple, pistillate. Disk-flowers yellow, tubular, perfect, their corollas mostly 5-lobed. 

 Anthers obtuse and entire at the base. Style-branches more or less flattened, their appendages 

 short, mostly rounded or obtuse. Achenes flattened, usually 2-nerved. Pappus-bristles fragile, 

 slender, scabrous or denticulate, in i series, or often an additional outer short series. [Greek, 

 early-old, alluding to the early hoary pappus.] 



