320 PLORA OF TEXAS. 



*■** Heads dioecious or TTwno&cious. 



Staminate and pistillate heads on the same plant. 



Fruitina: involucre 1-seeded, naked or tubcrcled '. Ambrosia. 



Fruiting involucre 2-8eeded, armed with hooked spines Xanthium. 



Staminate and pistillate heads on separate plants. 



Anthers tailed. Hoary herbs Antennaria. 



Anthers tailless. Smooth shrubs Bacchabis. 



§ 3. Heads radiate. 



Rays pistillate. 

 Flowers all fertile. 

 Receptacle naked. 

 Rays yellow. Leaves opposite. 



Pappus none Flavebia. 



Pappus scaly Pectis. 



Rays yellow. Leaves alternate. 



Scales of the involucre in 1 row Senecio. 



Scales of the involucre in 2 rows Helenium. 



Scales of the involucre in several rows Inula. 



Rays white or purple. 



Pappus none Leucanthemum. 



Pappus bristly Erigeron. 



Receptacle pitted. 

 Rays white or purple. 



Pappus double Diplopappus. 



Pappus single. Rays about 5. Achenia silky Sericocarpus. 



Pappus single. Rays numerous. Pappus bristly Aster. 



Pappus single. Rays numerous. Pappus scaly Boltonia. 



Rays yellow. 



Pappus double, of the ray and disk flowers alike Chrtsopsis. 



Pappus double, of the ray flowers none Heterotheca. 



Pappus single. 



Leaves opposite. Ueadd large, single or corymbose Arnica. 



Leaves alternate. Heads racemed or clustered Solidago. 



Leaves alternate. Heads panicled Isopappus. 



Receptacle chafly. 



Involucre double, the outer 4-leaved, 4-angled Tetbagonotheca. 



Involucre imbricated or spreading. 



Maritime shrubs. Pappus 4-toothed Bobbichia. 



Herbs. 

 Receptacle conical or elongated. 



Rays persistent. Corolla-lobes velvety Zinnia. 



Rays deciduous. Achenia 3-4-angled Heliopsis. 



Rays deciduous. Achenia compressed Spilanthes. 



Receptacle flat. 



Leaves lobed, alternate Achillea. 



Leaves not lobed. Pappus 2-awned Verbesina. 



Leaves not lobed. Pappus none Eclipta. 



Flowers of the disk sterile. 



Rays yellow. Pappus none Polymnia. 



Rays yellow. Pappus a toothed crown Chuysogonum. 



