AMBROSIACEAE. 



385 



1. Ambrosia elatior L. RAG- 

 WEED. ROMAN WORMWOOD. HOG- 

 WEED. WILD TANSY (Fig. 418.) 

 Annual, pubescent, puberulent or hir- 

 sute, paniculately branched, l-5 

 high. Leaves thin, l-2-pinnatifi<l, 

 petioled, 2 '-4' long, the upper alter- 

 nate, the lower mostly opposite, pale 

 or canescent beneath, the lobes ob- 

 long or lanceolate, obtuse or acute ; 

 racemes of sterile heads very numer- 

 ous, l'-6' long, the involucres hemi- 

 spheric, crenate; fertile heads obo- 

 void or subglobose, mostly clustered, 

 about 2" long, short-beaked, 4-6- 

 spined near the summit, sparingly 

 pubescent. [A. art emisiae folia L. ; 

 A. lieteropTiylla of Jones and of 

 Lefroy.] 



Common in waste and cultivated 

 grounds. Naturalized. Native of 

 North America. Flowers in summer 

 and autumn. 



Family 6. CARDUACEAE Neck. 

 THISTLE FAMILY. 



Herbs, rarely shrubs (some ti'opical forms trees), with watery or res- 

 inous (rarely milky) sap, and estipulate leaves. Flowers perfect, pistillate, 

 or neutral, or sometimes monoecious or dioecious, borne on a common re- 

 ceptacle, forming' heads, subtended by an involucre of bracts arranged in 

 one or more series. Receptacle naked, or with chaffy scales subtending 1 

 the flowers, smooth, or variously pitted or' honeycombed. Calyx-tube com- 

 pletely adnate to the ovary, the limb (pappus) of bristles, awns, teeth, 

 scales, or crown-like, or cup-like, or wanting. Corolla tubular, usually 5- 

 lobed or 5-cleft, the lobes valvate, or that of the marginal flowers of the 

 head expanded into a ligule (ray) ; when the ray-flowers are absent the 

 head is said to be discoid; when present, radiate; the tubular flowers form 

 the disk. Stamens usually 5, borne on the corolla and alternate with its 

 lobes, their anthers united into a tube (syngenesious), often appendaged 

 at the apex, sometimes sagittate or tailed at the base ; pollen-grains globose, 

 often rough or prickly. Ovary 1-celled ; ovule 1, anatropous ; style of fer- 

 tile flowers 2-cleft; stigmas marginal; style of sterile flowers commonly un- 

 divided. Fruit an achene. Seed erect; endosperm none; embryo straight; 

 hypocotyl inferior. About 800 genera and not less than 10,000 species, of 

 wide geographic distribution. In Kuhnia, the anthers are distinct, or 

 nearly so. 



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