338 THE KINDS OF PLANTS 



10. HELlANTHUS. Sunflower. 



Stout, often coarse perennials or annuals, with simple alternate or 

 opposite leaves and large yellow-rayed heads : ray florets neutral : scales of 

 involucre overlapping, more or less leafy: torus flat or convex, with a bract 

 embracing each floret akene 4-angled : pappus of two scales (sometimes 

 2 other smaller ones), which fall as soon as the fruit is ripe. 



a. Disk broivn. 



H. annuus, Linn. Common sunflower. Tall, rough, stout annual, with 

 mostly alternate stalked ovate-toothed large leaves : scales of involucre ovate- 

 acuminate, ciliate. Minnesota to Texas and west, but everywhere in gardens. 



H. rigidus, Desf. Prairie sunflower. Stout perennial (2-6 ft.), rough: 

 leaves oblong-lanceolate, entire or serrate, rough and grayish, thick and 

 rigid: heads nearly solitary, with 20-25 rays. Prairies, Michigan, west. 



aa. Disk yellow (anthers sometimes dark). 



H. giganteus, Linn. Tall, to 10 ft., rough or hairy : leaves mostly 

 alternate, lanceolate-pointed, finely serrate or quite entire, nearly sessile : 

 scales linear-lanceolate, hairy: rays pale yellow, 15-20. Low grounds. 



H. divaricatus, Linn. Figs 3, 4,23,27. Small for the genus, 1-4 ft.: 

 leaves opposite, ovate-lanceolate, 3-nerved, sessile, serrate, rough and 

 thickish : rays 8-12, 1 in. long. Common in dry thickets. 



H. tuberdsus, Linn. Jerusalem artichoke. Bearing edible stem-tubers 

 below ground: 5-10 ft.: leaves ovate to oblong-ovate, toothed, long-petioled: 

 scales not exceeding the disk: rays 12-20, large. Penn. west, and cultivated. 



11. TANACETUM. Tansy. 



Tufted perennials, with finely divided leaves and strong odor: involucre 

 of overlapping dry scales: torus convex: heads small, nearly or quite ray- 

 less, the flowers all seed-bearing: akenes angled or ribbed, bearing a short 

 crown-like pappus. 



T. vulgare, Linn. Common tansy from Europe, but run wild about old 

 houses: 2-4 ft. : leaves 1-3-pinnately cut: heads yellow, pappus-crown 5-lobed. 



12. CNiCUS. Thistle. 



Perennial or biennial herbs, with pinnatifld, very prickly leaves: florets 

 all tubular and usually all perfect : scales of the involucre prickly : torus bristly : 

 pappus of soft bristles, by means of which the fruit is carried in the wind. 



C. lanceolatus, Hoffm. Common thistle. Figs. 228-230, 276. Strong, 

 branching biennial : leaves pinnatifld, decurrent, woolly beneath : heads 

 large, purple, with all the involucre-scales prickly. Europe. 



C. arvensis, Hoffm. Canada thistle. Lower, perennial and a pestiferous 

 weed: leaves smooth or nearly so beneath: flowers rose-purple, in small, 

 imperfectly dioecious heads, only the outer scales prickly. Europe. 



13. Arctium, burdock. 



Coarse biennials or perennials, strong-scented, with large dock-like 

 simple leaves: head becoming a bur with hooked bristles, the florets all 

 tubular and perfect: torus bristly: pappus of short, rough, deciduous bristles. 



