DiETERiA. COMPOSITuE. 101 



ted, the heads larger, the involucre more hemispherical, with narrower and 

 more squarrose scales. 



* * Appendages of the style subulate or somewhat lanceolate : pap p\LS more slender . 



5. D. canescevs (Nutt.) : minutely canescent with a soft pubescence; stem 

 low, much branched, corymbose ; leaves linear, entire ; the radical spatu- 

 late ; scales of ilie obovoid involucre lanceolate, acute, imbricated in about 4 

 series, with slightly squarrose lips; rays (18-20) rather large, purplish-blue. 

 — Nutt. ! in trans. Amer. phil. soc. (n. ser.) 7. p. 300. Aster canescens, 

 Pursh ! Ji. 2. p. 547. A. biennis, Nutt. ! gen. 2. p. 155. 



Upper Missouri, in denudated argillaceous soils, from the Arikarees to Fort 

 Mandan. Nuttall ! (who alone has collected it.) Aug.-Oct. — Stem about a 

 foot high, divaricately branched, fasligiate at the summit, bearing numerous 

 heads about as large as a Daisy. Scales of the involucre rigiil, canescent, 

 with short greenish tips. Cauline leaves closely sessile, 1 to 2 inches long, 

 1 to 2 lines wide. Appendages of llie style subulate-lanceolate. 



6. D. pulverulenta (Nutt.) : somewhat cane.?cently puberulent; stem low, 

 much branched from the base, the branches fastigiaie, bearing few heads on 

 rather naked branchlets ; leaves linear or lanceolate ; the lower sparingly 

 toothed or spinulose-serrulate ; the uppermost entire ; scales of the hemi- 

 spherical involucre lanceolate, acute, imbricated in about 3 series; rays (6-12) 

 short, pale purple. — Nutt.! I. c. 



Arid plains towards the sources of the Platte, Nuttall! — About 6 inches 

 high. Nearly allied to the preceding; the heads smaller, the scales of the 

 involucre less imbricated, somewhat viscid ? Appendages of the style 

 subulate. 



§ 2. Scales of the hemispherical involucre nearly equal, imbricated in about 3 

 series, linear, with a short oppressed somewhat cartilaginous base, and 

 elongated acute spreading herbaceous tips : receptacle obscurely alveolate : 

 achenia obovate, many-striate : pappus of the ray and disk nearly equal: 

 leaves not rigid, pinnatifid and bipinnatifid. — Pappochkoma, Nutt. 



7. D. coronopifolia (Nutt.) : pubescent and somewhat viscid, diffusely 

 branched from the base ; the branches mostly terminated by single (showy) 

 heads; radical and lower leaves bipinnatifid, petioled ; the upper pinnatifid, 

 with the segments toothed or incised; rays (about 20) large, reddish-purjjle ; 

 achenia villous. — Nutt..' I. c. Chrysop.sis (Pappochronia) coronopifolia, 

 Nutt. ! in jour. acad. Philad. 7. p. 34. 



Dry naked places along streams, from the Upper Missouri and Platte to 

 the Rocky Moumalns, Mr. Wyeth .' Nuttall! Jiily-Aug. — Root annual or 

 biennial ? Stems 6-10 inches high. " Heads nearly as" large as the garden 

 Marigold." Scales of the involucre with long and loose herbaceous very 

 acute summits. Appendages of the style subulate. Achenia large, com- 

 pressed, but turgid, nearly as long as the pappus when mature. Pappus 

 reddish-brown, copious, rather rigid ; the bristles in 3 or more unequal series. 



25. SERICOCARPUS. Nees, Ast. p. 148 ; DC. j>rodr. 5. p. 261. 



Aster § Leucocoma, Nutt. (1834.) 



Heads 12-15-flowered ; the ray-flowers about 5, distant, pistillate; those 



of the disk tubular, perfect. Scales of the obovate-oblong or turbinate-cylin- 



drical involucre clo.sely imbricated in several series, nerveless or obscurely 



1-nerved ; the lower portion cartilaginous (whitish), appressed ; the apex 



