MOKOPETALOUS EXOGENOUS PLANTS. 321 



Rays yellow. Pappus 2-tootlied or awned. Achenia winged Silphium. 



Rays yellow. Pappus? 2-toothed or awned. Achenia wingless. .Berlandiera. 



Rayji white. Receptacle conical Parthenium. 



Rays neutral (without pistils). 

 Receptacle naked, or nearly so. 



Achenia villous. Pappus scaly, long-awned Qaillardia. 



Achenia smooth or the angles hairy. Pappus awnless Leptopoda. 



Receptacle deeply pitted. 



Margins of the pits entire. Perennial Baldwinia. 



Margin? of the pits toothed. Annual Actinospermum. 



Receptacle chaffy throughout. 



Involucre double. Pappus 2-4-awned. 



Awns of pappus hi?pid upward Coreopsis. 



Awns of pappus hispid downward. Achenia beakless Bidens. 



Awns of pappus hispid downward. Achenia beaked Cosmos. 



Involucre simple or imbricate. 

 Pappus a cup-shaped border, or none. 



Chaff of the receptacle elongated, spine-pointed Echinacea. 



Chaff of the receptacle not elongated nor spine-pointed Rudbeckia. 



Pappus 2-4-awned. 



Achenia winged. Leaves divided Lepachts. 



Achenia winged Leaves undivided .'.Actinomeris. 



Achenia wingless. Awns of the pappus deciduous Helianthus. 



Achenia wingless. Awns of the pappus persistent Helianthblla. 



Receptacle chaffy Achenia ribbed Maruta. 



Sub-order II. Labiatiflorae. Corolla of the perfect 

 flowers 2-lipped; tlie outer lip 3-lobed, the inner 2-lobed. 



Herb steraless. Scape 1-flowered. Flower nodding Chaptalia. 



Sub-order III. Liguliflorae. Corolla ofall the flowers 

 ligulate. 



Pappus none. Achenia many-ribbed Apogon. 



Pappus scaly and bristly. 



Scales of the pappus 5, with 5 intermediate bristles Krigia. 



Scales of the pappus and bristles numerous Cynthia. 



Pappus hairy. 

 Pappus tawny or dirty white. 



Flowers erect, rose-color. Leaves filiform Ltgodesmia. 



Flowers erect, yellow. Achenia beakless Hierachjk. 



Flowers erect, yellow. Arhenia long-beaked Ptrrhopappus, 



Flowers nodding, whitish or purplish Nabalu?. 



Pappus clear white (except in one Mulgedium). 

 Achenia conspicuously beaked. 



Achenia rii»bi^d. Stemless herbs Taraxacum, 



Achenia flat. Stems leafy Lactuca. 



Achenia beakless, or nearly so. 



Flowers blue. Achenia slightly beaked Mulgedittm. 



Flowers yellow. Achenia beakless Sonchus. 



14* 



