MONOPETALOUS EXOGENOUS PLANTS. 319 



Receptacle bristlj'. 



Leaves spiny Cirsium. 



Leaver not t^piny , cordate Lappa. 



Receptacle naked. 



Scales of tlie involucre in a single row Cacalia. 



Scales of the involucre in 2 or more rows. 



Pappus double, the outer row very short Vernonia. 



Pappus single. 

 Achcnia ribbed or striate. 



Pappus plumose. Flowers cream-colored Kuhnia. 



Pappus scabrous. Leaves cordate Brickellia. 



Pappus scabrous. Leaves not cordate Liatris. 



Achenia not ribbed, 5-angled 



Receptacle conical Conoclinium. 



Receptacle flat. Stems climbling Mikania. 



Receptacle flat. Stems erect Eupatorium. 



P*ppns scaly. 

 Flowers blue or purple. 



Pappus a cup-shaped border of united scales Ccei-estina. 



Pappus slender, almost bristly. 



Pappus deciduous. Heads large and single Stokesia. 



Pappus persistent. Heads small, in 3-bracted clusters Elephantopus. 



Pappus of 5 oval almost bony scales. Leaves whorled Sclerolepis. 



Flowers white. 

 Receptacle naked. 



Leaves entire, linear or lanceolate Palafoxia. 



Leaves entire, ovate or cordate Ageratum. 



Leaves pinnately lobed Hymenofappus. 



Receptacle chaffy. 



Acheniuin top-shaped. Scales of the pappus 5-6 Marshallia. 



Acbenium flat. Pappus 2-awned Actinomeris. 



Flowers yellow. Pappus 2-4-awned. 



Awns of the pappus deciduous Helianthus. 



Awns of the pappus persistent, hispid upward Coreopsis. 



Awns of the pappus persistent, hispid downward Bidens. 



** Heads withfloioers variously imperfect. 



Marginal flowers pistillate. Central flowers perfect. 

 Pappus bristly. 



Scales of the involucre in a single row Erechthites. 



Scales of the involucre in 2 or more rows. 



Involucre persistent. Leaves sinuate-lobed Conyza. 



Involucre persistent. Leaves entire. Anthers tailed Plucuka. 



Involucre persistent. Leaves entire. Anthers tailless Gnaphamum. 



Involucre deciduous. Heads spiked Pterocaulon. 



Pappus not bristly, 5-lobed Tanacetum. 



Pappus none Artemisia. 



Marginal flowers pistillate. Central flowers staminate. 



Pappus none. Style rigid, persistent Solita. 



Pappus none. Style deciduous. Heads nodding IVA. 



Marginal flowers neutral. Central flowers perfect Centaxjrea. 



