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FLORA OF THE DISTRICT OF COLUMBIA. 269 



Bracts ending in straight spines or sometimes not spiny. 



Flower heads small, the body of the involucre less than 1 cm. thick, the 

 bracts merely toothed or else ending in very stout spines longer than the 

 involucre; plants usually low annuals; scar of insertion of the fruit on 



the side just above the base 50. CENTATTREA. 



Flower heads usually large, the body of the involucre commonly 2-5 cm. 



thick or, if small, the bracts ending in short slender spines; plants 



usually very large and stout, biennials or perennials; scar of insertion of 



the fruit basal. 



Pappus bristles feather-like (plumose); receptacle bearing numerous 



bristles 48. CIESIXTM. 



Pappus bristles smooth or nearly so, not plumose; receptacle without 



bristles 49. ONOPORDON. 



BB . Leaves never with spiny teeth, the bracts not armed with spines, not toothed. 

 Leaves, at least the lower ones, lobed nearly or quite to the midrib; flowers 

 bright yellow or greenish yellow, the heads small. PlantB usually strong- 

 scented . 

 Blades of the upper leaves oblong or ovate, merely shallow-toothed or with a 

 few deep lobes at the base. Flower heads in a usually flat-topped 



corymb; pappus a short crown 39. CHRYSANTHEMUM. 



Blades of all the leaves divided into narrow lobes. 

 Flower heads in a flat-topped corymb, the flowers bright yellow; pappus a 



short crown 40. TANACETUM. 



Flower heads in long narrow racemes or panicles, the flowers greenish 



yellow; pappus none 41. ARTEMISIA. 



Leaves entire to coarsely toothed, never lobed nearly to the midrib; flowers 



white, blue, or purple, or sometimes only whitish, never conspicuously 



yellow. 



Leaves with copious white woolly pubescence. Plants herbaceous; flowers 



white, in small heads. 



Leaves mostly basal, broad and spatulate, those of the stems small and 



narrow; plants perennial, with long prostrate stolons, often forming 



mats, the flowering stems simple below, bearing 1 or more heads at or 



near the summit -20. ANTENNARIA. 



Leaves all borne on the stems, linear or very narrow; plants never with 



stolons; much branched annuals or winter annuals, never forming mats. 



Receptacle of the flower head bearing cbafllike scales; leaves crowded, 



usually erect or apposed to the stems, linear 18. GIEOLA. 



Receptacle of the flower head without scales; leaves usually not crowded, 

 spreading or ascending, linear to narrowly spatulate. 



21. GNAPHALITJM. 

 Leaves never with white woolly pubescence. 

 Plants shrubby. Leaves coarsely toothed, glabrous; flowers white; pappus 



of the fertile heads of very long bristles 17. BACCHARIS. 



Plants herbaceous. 



Flower heads collected in dense heads surrounded by leaflike bracts. 

 Plants hairy, with numerous large basal leaves, the flowers bluish, 



2-5 in each head 2. ELEPHANTOPUS. 



Flower heads in racemes, spikes, corymbs, or panicles, never in dense 

 heads. 

 Flower heads in long racemes or spikes; stems simple. Flowers rose- 

 purple, very showy; perennials, more or less pubescent, with nar- 

 row entire rigid leaves 6. LACTNARIA. 



Flower heads in corymbs or panicles; stems usually conspicuously 

 branched. 



