THISTLE FAMILY 893 



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

 or lacerate edges. Ray-flowers numerous, pistillate; lisulcs 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. liigh; 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 tlie bracts long, reflexed-squarrose. 3. M. tanacctifolia. 



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



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

 squarrose refle.xed. 

 Stem and inflorescence distinctly viscid. 



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



Leaves tliin, coarsely but not sahently dentate; bracts over 1 mm. wide. 



4. AT. Bigelovii. 

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



mm. wide. 

 Achenes glabrous or minutely pubescent; stem glabrous below. 



5. A/, varians. 

 Achenes strigose; stem glandular -hispid tliroughout. 6. M. aspera. 



Stem-leaves linear or oblanceoiate, 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. Paltcrsonii. 

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



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



.sessile. 9. M. sessiliflora. 



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

 pedimcled. 

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



Stem-leaves oblanceoiate. 11. M. lati folia. 



Bracts Une^r, 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 oblanceoiate; 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. 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. leplophylla. 

 Leaves tliick. 



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



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

 Stem divaricately branched, low; upper leaves small, linear 

 or some Unear-oblanceolate. 18. M. pulrerulenla. 



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

 late, coarsely toothed. 19. M. divaricata. 

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



Stem i)uberulent or glabrate, irlandular only on the inflorescence. 

 Bracts slightly if at all squarrose. 



Stem slender, with strongly ascending branches; leaves subentire. 



20. A/, glabella. 

 Stem divaricately branched; lower leaves sharply toothed. 



21. M. ramosa. 

 Bracts strongly reflexed-squarrose. 



Leaves aU, except those of the smaller branches, toothed; achenes sti-i- 



gose. 22. M. Selbyi. 



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



Stem densely glandular-liispid. 



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



24. A/, cichoriacea. 

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



25. M. Fremontii. 



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

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



