FLORA OF THE DISTRICT OF COLUMBIA. 279 



12. ASTER L.i AsTEH. 



Leaves, at least the lowest ones, petioled, the petioles not winged, the blades more or 



less cordate at the base (rarely only truncate), usually heart-shaped. 



Stem leaves, at least most of them, with sessile clasping bases. Rays pale blue to 



violet. 6. A. undulatus. 



Stem leaves never with sessile clasping bases, usually petioled, sometimes sessile. 



Leaves all entire, 3.5 cm. wide or less, the larger ones more than twice as long as 



broad. Rays violet-blue 3. A. shortii. 



Leaves, at least the lower ones, conspicuously toothed, the larger ones much 



wider, less than twice as long as broad. 



Heads panicled; rays usually pale blue. Bracts narrow, with conspicuous, 



sharply defined, green tips. 



Bracts obtuse; involucre about 5 mm. high 4. A. cordifolius. 



Bracts very acute; involucre about 6 mm. high 5. A. sagittifolius. 



Heads in flat-topped or round-topped corymbs; rays white or pink. 



Leaves thin, mostly smooth, the teeth spreading, very acute. 



1. A. divarlcatus. 



Leaves usually thick and firm, often rough on the upper surface; the teeth 

 low, rounded or very obtuse and abruptly short-pointed. .2. A. schreberi. 

 Leaves never both cordate at the base and petioled, sometimes cordate at the base 

 but then sessile. 

 Stem leaves with a clasping sessile base, or if not very conspicuously clasping at least 

 evidently broadened at the base, or the leaves sometimes with winged petioles 

 and these broadened and clasping at the base. 

 Stems hairy throughout. 

 Leaves, at least most of them, conspicuously toothed. Rays lilac-blue to white. 



10. A. puniceus. 

 Leaves entire. 

 Heads comparatively small, the disk 8-12 mm. broad; leaves only slightly 

 clasping or merely broadened at the base. Bracts very viscid; rays 



violet-purple 9. A. oblongifolius. 



Heads large, the disk 12-16 mm. broad; leaves strongly clasping. 

 Stem rough with very short or minute hairs; leaves often narrowed just 

 above the base; involucre 6-7 mm. long, the bracts close, with slightly 



spreading tips; rays mostly blue-purple 7. A. patens. 



Stem hirsute with long hairs; leaves not narrowed above the base; in- 

 volucre 8-10 mm. long, the bracts loose and spreading; rays violet- 

 purple 8. A. novae-angliae. 



Stems glabrous below, sometimes hairy above. 



Lower leaves abruptly contracted into long, narrowly winged petioles, the 

 blades mostly ovate, all of them sharply toothed. Rays violet. 



11. A. prenanthoides. 

 Lower leaves slightly if at all contracted, the petioles, if any, very broadly 

 winged, the blades oblong to linear, entire or remotely toothed, those of 

 the upper leaves always entire. 



' Some of the species of this genus are extremely variable and many of the forms 

 which are regarded by most botanists as mere variants have been described as spe- 

 cies, E. S. Burgess, for instance, in his "Species and variations of Biotian Asters" 

 (Mem. Torrey Club 13. 1906), described about 80 new species of the group repre- 

 sented with us by A. divaricatus and A. schreberi, but only one of these is accepted 

 in the last edition of Gray's Manual. Many of them were reported from our region, 

 but they appear to be distinguished by unstable characters. A conservative view 

 has been adopted in the present treatment, and the two species mentioned above 

 have been accepted in their usual sense. 



