322 FLORA OF PHILADELPHIA. 



1. Heads 4-6 mm. high, chiefly in axillary clusters; achenes pubescent. 

 Stem and branches terete ; leaves lanceolate to oblong. 2. S. caesia. 

 Stem and branches grooved and angled. 3. S. flexicaulis. 



2. Heads 4-6 mm. high, chiefly in a terminal spike-like thyrsus; achenes gla- 

 brous or nearly so. 

 Eays white, stem pubescent. 4. S. bicolor. 



Rays yellow ; stem densely pubescent. 5. S. hispida. 



Rays yellow ; stem glabrous or sjiaringly pubescent ; leaves thick. 



6. S. erecta. 

 Heads in a terminal simple or branched thyrsus, not at all secund on its 

 branches, or scarcely so. 

 Bracts of the involucre acute or acutish. 7. S. puberula. 



Bracts of the involucre obtuse (or the inner acutish in No. 8). 

 Upper leaves abruptly smaller than the lower, appressed. 



8. S. stricta. 

 Leaves gradually smaller upward, spreading or ascending. 



Lower leaves large, oblong or oval, acute or obtusish. 



9. S. speciosa. 

 Basal leaves narrowly spatvilate. 10. S. Purshii. 



Heads in a terminal, usually large panicle, secund on its spreading or 

 recurved branches. 

 Plant maritime; leaves thick, fleshy, entire. 11. S. sempervirens. 

 Plants not maritime; leaves not fleshy. 



1. Leaves pinnately veined, not triple-nerved. 

 Leaves all entire, thin and glabrous. 12. S. odora. 



Leaves, at least the lower, more or less dentate or serrate. 

 Stem densely pubescent ; leaves more or less so. 



Leaves rugose-veiny beneath, sharply serrate. 13. S. rugosa. 

 Leaves not rugose, sparingly dentate or entire. 14. S. flstulosa. 

 Stem glabrous, or puberulent, or pubescent only above. 

 Leaves very scabrous on the upper surface, serrulate. 



15. S. patula. 

 Leaves smooth, or minutely roughened on the upper surface (pubes- 

 cent in forms of No. 19). 



Racemes few, widely divergent, very slender. 



16. S. ulmifolia. 

 Racemes numerous, spreading, recurved, or ascending. 



Leaves all oblong or oblong-lanceolate, sessile. 



17. S. Elliottii. 



At least the lower leaves petioled, lanceolate or ovate- 

 lanceolate. 



Leaves firm, ovate-lanceolate or oblong-lanceolate; 

 heads about 4 mm. high ; racemes short ; rays sev- 

 eral. 18. S. neglecta. 



Leaves firm, lanceolate or oval-lanceolate ; heads 3-4 

 mm. high ; racemes numerous, slender. 



19. S. juncea. 

 Leaves thin, the lower broadly ovate, short-acuminate ; 



heads 5-7 mm. high ; racemes numerous. 



20. S. arguta. 



S. Leaves triple-nei'ved, i. e., tvith a pair of lateral veins stronger than the 



others, these often obscure in No. 23. 

 Stem glabrous; bracts of the involucre oJ)tuse. 21. 8. serotina. 



Stem pubescent or scabrous. 



Leaves lanceolate, sharply serrate or entire, rough above. 



22. S. Canadensis. 

 Leaves oblanceolate, spatulate, oblong or oval; the lower crenate. 



23. S. nemoralis. 

 Heads in a tenninal, corymbiform, sometimes thyrsoid cyme, form- 

 ing a flat-top23ed inflorescence. 24. S. rigida. 



