THISTLE FAMILY 893 



herbaceous tips, imbricate in several series; receptacle pitted, the pits with toothed 

 or lacerate edges. Ray-flowers numerous, pistillate; ligules violet or purple. 

 Disk-flowers perfect; corollas yellow, turning red or brown. Anthers rounded 

 at the base. Style-branches with subulate or lanceolate, acute appendages. 

 Achenes turbinate, pubescent or glabrate. Pappus of numerous firm rough 

 bristles. 



Leaves once or twice pinnatifld; root annual; achenes terete. 

 Green tips of the bracts short, not squarrose. 



Heads 6-7 mm. high; plant 3-5 dm. high. 1. M. parviflora. 



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



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



Leaves spinulose-toothed; plant perennial or biennial; achenes compressed. 



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



squarrose reflexed. 

 Stem and inflorescence distinctly viscid. 



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. viscosula. 



Plant 1-2 (seldom 3) dm. high; heads solitary or few. 8. M. Patter sonii. 

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



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

 sessile. 9. M. sessiliflora. 

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



ped uncled. 



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 47 series with squarrose tips. 



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



as the lower ones. 15. M. commixta. 



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. 



16. M. leptophylla. 

 Leaves thick. 



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. pulverulenta. 



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

 late, coarsely toothed. 19. M. diraricata. 

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



Stem puberulent or glabrate, glandular only on the inflorescence. 

 Bracts slightly 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. M. spectabilis. 

 Stem densely glandular-hispid. 



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



24. M. cichonacea. 

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



1. M. parviflora A. Gray. Annual; stem 3-5 dm. high, branched, glabrous 

 or nearly so; leaves sparingly glandular, simply pinnatifid; lobes short, linear, 



