THISTLE FAMILY 245 



Heads about 1 cm Wgh; plant low, 1-2 dm. laigh. 2. M. humilis. 



Green tips of the bracts long, reflexed-squarrose. 3. M. tanacetifolia. 



Leaves spinulose-tootlied; plant perennial or biennial; aclienes compressed. 



Bracts linear-subulate: green tips in most longer than the straw-colored lower portion, 

 squarrose reflexed. 

 Stem and inflorescence distinctly -vascid. 



Stem-leaves lanceolate or oblong, usually distinctly triple-veined. 



Leaves thin, coarsely but not saliently dentate; bracts over 1 mm. wide. 



4. M. Bigelovii. 

 Leaves thick with salient teeth; plant very glandular; bracts less than 1 

 mm. wide. 

 Achenes glabrous or minutely pubescent; stem glabrous below. 



,5. M. varians. 

 Achenes strigose: stem glandular -hispid throughout. 6. M. aspera. 

 Stem-leaves linear or oblanceolate, 1 -nerved. 



Plant 3-5 dm. high: heads numerous in a panicle or raceme. 



7. M. riscosula. 

 Plant 1-2 (seldom 3) dm. liigh; heads solitary or few. 8. M. Paliersonii. 

 Stem strigose-puberulent : involucre slightly if at all viscid. 



Leaves all saliently toothed; inflorescence narrow, racemiform; heads sub- 

 sessile. 9. M. sessiliflora. 

 Leaves except the lowest entire or denticulate; inflorescence open; heads 

 peduncled. 

 Stem-leaves narrowly linear. 10. M. rubricaulis. 

 Stem-leaves oblanceolate. 11. M. latifolia. 

 Bracts linear, with a lanceolate or rhombic green tip, which is usually much shorter 

 than the straw-colored lower portion. 

 Leaves cinereous. 



Bracts canescent, scarcely at all viscid or glandular. 



Stem-leaves linear; plant erect. 12. M. canescens. 



Stem-leaves narrowly oblanceolate; plant diffuse. 13. M. superba. 



Bracts densely viscid or glandular, especially the tips. 



Bracts in but 3 series, not at all squarrose; the outer wholly greenish. 



14. M. angustifolia. 

 Bracts in 4-7 series with squarrose tips. 



Stem 1-2 dm. high; upper stem-leaves ample, almost as large and broad 



as the lower ones. 15. M. commiila. 



Stem 2-4 dm. high: upper stem-leaves smaller and narrower than the 

 lower ones. 

 Heads distinctly peduncled. 



Leaves very thin; stem-leaves entire or nearly so. 



IG. M. leplophylla. 

 Leaves tliick. 



Stem erect, rather simple; stem-leaves linear-oblanceolate 



or oblanceolate, spinulose-toothed. 17. M. viscosa. 

 Stem divaricately branched, low; upper leaves small, linear 

 or some linear-oblanceolate. 18. M. puhcrulenta. 



Heads subsessile, racemosely disposed; stem-leaves linear-oblanceo- 

 late, coarsely toothed. 19. i\/. diraricala. 

 Leaves glabrous, or glandular-hispid or scabrous, not cinereous. 



Stem puberulent or glabrate, glandular only on the inflorescence. 

 Bracts shghtly if at all squarrose. 



Stem slender, with strongly ascending branches; leaves subentire. 



20. M. glabella. 

 Stem divaricately branched; lower leaves sharply toothed. 



21. M. ramosa. 

 Bracts strongly reflexed-squarrose. 



Leaves all, except those of the smaller branches, toothed; achenes stri- 

 gose. 22, M. Selbyi. 

 Leaves all entire; achenes glabrous. 23. JM. spectabilis 

 Stem densely glandular-hispid. 



Bracts more or less glandular-pubescent and with squarrose tips. 



24. M. cichoriacea. 

 Bracts grayish puberulent; tips short, lanceolate, not squarrose. 



25. A/. Fremontii. 



45. ERIGERON L. Fleab.\ne. 



Bracts of the involucre in 1-2 series of almost equal length, not thickened on the back. 

 Rays inconspicuous, erect or ascending, usually involute and incurved, numerous; 

 often inside them a series of rayless pistillate flowers; leaves entire. 



I. Acres. 

 Rays conspicuous, spreading, flat; no rayless pistillate flowers inside. 

 Plant without runners. 



Perennials with rootstocks or woody caudices. 



Leaves dissected or deeply cleft. III. COMPOSITI. 



Leaves entire or merely toothed. 



Stems low, less than 2 dm. high, scapiform, usually bearing only one 

 head; stem-leaves usually reduced. 

 Involucre and peduncles villous with many-celled hairs; bracts 



comparatively broad. II. UxiFLORi. 



Involucre and peduncles hirsute to glandular-puberulent or glabrate, 

 not long-villous. IV. Radic.\ti. 



