KEY TO GENERA. THISTLE FAMILY. 347 



Family 46. COMPOSITAE Adans. Fam. PI. 2 : 103. 1763. 

 THISTLE FAMILY. 



Herbs, rarely shrubs (some tropical forms trees), with watery or resinous 

 (rarely milky) sap, and opposite alternate or basal exstipulate leaves. Flowers 

 perfect, pistillate, or neutral, or sometimes monoecious or dioecious, borne on a 

 common receptacle, forming heads, subtended by an involucre of few to many bracts 

 arranged in one or more series. Receptacle naked, or with chaffy scales subtend- 

 ing 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 i-celled; ovule I, anatropous ; style of 

 fertile flowers 2-cleft, its branches variously appendaged, or unappendaged; stigmas 

 marginal ; style of sterile flowers commonly undivided. 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. The family 

 is also known as CARDUACEAE, AGGREGATAE, and by the English name of Aster-worts. In Kuhnia, the 

 anthers are distinct, or nearly so. 



* Anthers not tailed at the base ; stigmatic lines of the style-branches only at the base, or not extending 

 beyond the middle; flowers all tubular and perfect, never yellow; rays none. 



Style-branches filiform or subulate, hispidulous ; receptacle naked. Tribe i. VERNONIEAE. 



Style-branches thickened upward, obtuse, papillose. Tribe 2. EUPATORIEAE. 



** Anthers tailed at the base, unappendaged at the tip; heads small; rays none (except in Inula where they 



are large, yellow). Tribe 4. INULEAE. 



*** Anthers not tailed at the base ; stigmatic lines of the style-branches in the perfect flowers extending to 

 the summit; flowers tubular only, or tubular and radiate, often yellow. 



i. Receptacle naked (see also Nos. 85-88 of Tribe 7). 



a. Bracts of the involucre usually well imbricated. 



Style-branches of the perfect flowers flattened, with terminal appendages. Tribe 3. ASTEREAE. 

 Style-branches truncate, or with hairy tips. Tribe 6. HELENIEAE. 



b. Bracts little imbricated, or not at all ; pappus of soft bristles. 



Tribe 8. SENECIONEAE. 



2. Receptacle chaffy (except in Nos. 85-88). 



Bracts of the involucre herbaceous or foliaceous ; not scarious. Tribe 5. HELIANTHEAE. 



Bracts of the involucre dry, scarious. Tribe 7. ANTHEMIDEAE. 



**** Anthers long-tailed at the base, with elongated appendages at the tip; heads large; rays none (in 



Centaurea often with enlarged marginal flowers) ; bracts imbricated. 



Tribe 9. CYNAREAE. 



Tribe i. VERNONIEAE. 



Pappus double, the inner of rough capillary bristles, the outer of scales, or short bristles ; heads 



not glomerate. i- Vernonia. 



Pappus a single series of bristles ; heads glomerate, subtended by sessile bracts. 2. Elephantopus. 



Tribe 2. EUPATORIEAE. 



* Achenes 3-s-angled, not ribbed. 



Pappus of 5 broad obtuse scales ; aquatic herb with linear whorled leaves. 3. Sclerolepis. 



Pappus of numerous capillary bristles. 



Involucre of more than 4 bracts ; erect herbs. 4- Eupatorium. 



Involucre of 4 bracts ; our species twining herbaceous vines. 5. Mikania. 



** Achenes 8-io-ribbed, or 8-io-striate. 



I. Bracts of the involucre in several series, the outer successively shorter. 

 Bracts of the involucre strongly striate-nerved ; heads panicled or corymbed in our species. 



Pappus-bristles rough or serrate ; involucral bracts numerous. 6. Coleosanthus. 



Pappus-bristles plumose ; involucral bracts few. 7- Kuhnia. 



Bracts of the involucre faintly striate, if at all ; heads spiked or racemed. 8. Lacinaria. 



2. Bracts of the involucre in only 2 or 3 series ; all nearly equal. 



9. Trilisa. 



Tribe 3. ASTEREAE. 

 A. Ray-flowers yellow (white in one species of Solidago), or wanting; plants not dioecious. 



* Pappus of scales, or awns, or wanting, never of numerous capillary bristles. 



Heads small, not over 2" high ; leaves narrowly linear, entire. 



Perennial herbs, or shrubs; all the flowers fertile. 10. Guherresia. 



