Vol. III.] 



THISTLE FAMILY. 



R^ys larpe, neutral; receptacle deeply honey-combed. 

 Rays none; scales of the receptacle narrow, rigid. 



70. 



/I- 



Actinospenn n w. 



RIarshallia. 



Tribe 6. Hei.Exie.xe. 



A. Ray-flowers persistent on the achenes, falling away with them, papery. 72. Psiloslroplie. 

 B. Ray-floweis deciduous or wanting. 

 •K Plants not dotted with oil-glands. 



a. Pappus none, 75. Ftaiteria. 



b. Pappus present (in all our species), of separate scales or bristles. 

 1. Bracts of the involucre petal-like, colored, their margins and apices scarious. 

 Leaves, at least the lower, pinnately parted, or pinnatifid; rays none; corolla-lobes of disk-flowers 



ovate. 74. Hvmenopappus. 



Leaves entire; rays present, or none; corolla-lobes of disk-flowers linear. 75. Polypteris. 

 2. Bracts of the involucre herbaceous, not scarions-tipped, nor petal-like, appressed, or spreading. 

 Receptacle naked. 



Bracts of tlie involucre appressed. 



Achenes 4-angkd, linear or oblong. 76. Bahia. 



Achenes 5-10 ribbed or 5-10 angled, top-shaped, 77. Picradenia. 



Bracts of the involucre spreading, or refle.xed at niaturitj-. 78. Helenium. 



Receptacle with bristle-like chatT. 79. Galliardia. 



-:f -:■:- Plants dotted with oil-glands, especially the leaves and involucre, 

 Involucral bracts more or less united; style-branches of the disk-flowers elongated. 



Involucral bracts united at the base. 80. Dvsodia. 



Involucral bracts united high up into a cup. 81. Thymop/tylla. 



Invjlucral bracts separate; style branches of the disk-flowers very short. 82. Pedis. 



Tribe 7. Anthemideae. 



-:■:- Receptacle chafTy. 

 .A-chenes flattened: involucre obovoid to canipanulate; heads small. 83. Achillea. 



.\chenes terete; involucre hemispheric; heads large. 84. Anlhemis. 



-:■:- r;- Receptacle not chafTy, naked, or sometimes hairy, 

 1, Ray-flowers usually present, sometimes wanting; rays large. 



Chrysanthemum. 

 Matricaria. 



Tanacelum. 

 Artemisia. 



Tussilago. 



Petasites. 



Arnica. 



92, Erechtites. 



Receptacle flat to hemispheric; bracts of the involucre in several series, 85. 



Receptacle conic to ovoid; bracts in few series; rays white or none. 86. 



2. Ray flowers none; heads small. 



Heads corymbed; pappus a short crown: flowers yellow. 87. 



Heads racemose, spicate or panicled; pappus none. 88. 



Tribe 8. Senecioneae. 



Leaves all basal ; heads on scapes. 



Head solitary; flowers yellow. 89. 



Heads corymbed ; flowers white or purple. 90. 



Leaves opposite; rays yellow. 91. 



Leaves alternate. 



Flowers white, whitish or pinkish; rays none. 



Marginal flowers pistillate; disk-flowers perfect. 

 Flowers all perfect. 



Involucre of about 5 bracts; sap milky. 93. Mesadenia. 



Involucre of about 12 bracts and several smaller outer ones. 94. Synosma. 



Flowers yellow; ray-flowers mostly present. 95. Senecio. 



Tribe 9. Cvxareae. 



-;;- Achenes inserted on the receptacle by their bases, not oblique. 

 Receptacle densely bristly. 

 Filaments separate. 



Involucral bracts hooked at the tip; leaves not bristly. 96, Arctium. 



Involucral bracts not hooked; leaves bristly. 97. Carduns. 



Filaments united below. 98. Mariana. 



Receptacle fleshy, not bristly. 99. Onopordon. 



-)\- -;^ Achenes obliquely inserted on the receptacle. 



Heads not subtended by bristly leaves; involucral bracts often bristly. 100. Centaurea. 



Heads sessile, subtended by bristly leaves. loi. Cnicus. 



I. VERNONIA Schreb. Gen. PI. 2: 541. 1791. 



Erect brancliitig perennial herbs, or some tropical species shrubby, with alternate (very 

 rarely opposite), in our species sessile leaves, and discoid cymose-paniculate heads of purple 

 pink or white tubular flowers. Involucre hemispheric, campanulate or oblong-cylitidric, its 

 bracts imbricated in several or many series. Receptacle flat, naked. Corolla regular, 5-cleft. 

 Anthers sagittate at the base, not caudate. Style-branches subulate, hispidulous their whole 

 length. Achenes S-ioribbed, truncate. Pappus of our species in 2 scries, the inner of nu- 

 merous roughened capillary bristles, the outer of much shorter small scales or stout bristles. 

 [Named after William Vernon, English botanist.] 



.\bout 475 species, of wide distribution in warm-temperate regions, most abundant in South 

 America. IJesides the following, 2 others occur in the southern and southwestern United States, 

 Bracts of the hemispheric involucre, or some of them, with subulate or filiform lips. 



Involucre 3"-5" broad, its bracts shorter than the liead. i, V. Noveboracensis. 



Involucre 9"-i2" broad, its bracts as long as the head. 2. V. crinila. 



Bracts of the involucre merely acute, obtuse, or truncate. 



Leaves lanceolate to oval, pinnately veined. 



Bracts of the involucre with squarrose refle.xed tips. 3. V. Baldwinii. 



