COMPOSITE. 65 



2. Onopor'don. Leaves and scales of the involucre prickly. Heads much 



as in Cirsium, but the receptacle naked, and deeply honeycombed. 

 Pappus of long bristles, nut plumose. Stem winged by the decurrent 

 bases of the leaves. Flowers purple. 



3. I^ap'pa. Leaves not prickly, but the scales of the globular involucre 



tipped with hooked bristles. Pappus of many short rough bristles. 

 Receptacle bristly. Flowers purple. 



i- -i- Marginal florets sterile, and their corollas much larger than the others, 

 forming a kind of false ray. 



4. Centaure'a. Leaves not prickly. Scales of the involucre fringed. Pappus 



very short. Receptacle bristly. Flowers blue. 



*->-*- Sterile and fertile florets in separate heads, i.e., monoecious. Fruit 

 a completely closed involucre (usually bristly) containing only one or two 

 florets, these heads sessile in the axils of the bracts or upper leaves. Sterile 

 heads with more numerous florets in flatfish involucres, and forming racemes 

 or spikes. Papptis none. 



5. Xaii'thium. Fertile florets only 2 together in burs with hooked prickles, 



clustered in the axils. Sterile heads in short spikes above them, the 

 scales of their involucres in one row only, but not united together. 



6. Ambro'sia. Fertile florets single, in a closed involucre armed with a few 



spines at the top. Sterile heads in racemes or spikes above, the scales 

 of their involucres in a single row and united into a cup. 



* * Scales of the involucre without bristles of any kind. 



HE- Marginal florets without stamens. 

 *+ Pappus none or minute. Receptacle naked. Very strong-scented herbs. 



7. Tanace'tum. Flowers yellow, in numerous corymbed heads. Scales of 



the involucre dry, imbricated. Pappus 5-lobed. Leaves dissected. 



8. Arteinis'ia. Flowers yellowish or dull purplish, in numerous small heads 



which are panicled or racemed. Scales of the involucre with dry and 

 scarious margins, imbricated. Hoary herbs. 



*+ *+ Pappus of all the florets bristly. Receptacle naked. 



9. Erpchthi'tes. Flowers whitish. Scales of the involucre in a single row, 



linear, with a few bractlels at the base. Corolla of the marginal florets 

 very slender. Pappus copious, of fine soft white hairs. Heads corymbed. 

 Erect and coarse herbs. 



10. Gnapha'lium. Flowers whitish or yellowish. Scales of the involucre 



yellowish- white, in many rows, dry and scarious, woolly at the base. 

 Outer corollas slender. Pappus a single row of fine rough bristles. 

 Flocculent-woolly herbs. 



11. Anteima'ria. Very much like Gnaphalium in appearance, being white- 



woolly, but the heads are usually dioecious, and the bristles of the 

 pappus thicker in the sterile florets. 



