274 COMPOSITE. (COMPOSITE FAMILY.) 



*- * Leaves green both sides, or only with loose cobwebby hairs underneath : scales of 

 the involucre scarcely prickly-pointed : heads large. 



7. C. mtlticum, Michx. (SWAMP THISTLE.) Stem tall (3 -8 high), 

 angled, smoothish, panicled at the summit, the branches sparingly leafy and 

 bearing single or few rather large naked heads ; leaves somewhat hairy above, 

 whitened with loose webby hairs beneath when young, deeply pinnatifid, the divisions 

 lanceolate, acute, cut-lobed, prickly-pointed; scales of the webby and glutinous invo- 

 lucre closely appressed, pointless or barely mucronate ; flowers purple ; root per- 

 ennial. Swamps and low woods : common. 



8. C. pumilum, Spreng. (PASTURE THISTLE.) Stem low and stout 

 (l-3 high), hairy, bearing 1-3 very large heads (!' broad), which are some- 

 what leafy-bracted at the base ; leaves green, lanceolate-oblong, partly clasping, 

 somewhat hairy, pinnatifid, with short and cut very prickly-margined lobes ; outer scales 

 of the involucre prickly-pointed, the inner very slender ; flowers purple or rarely 

 white (fragrant, 2' long) ; root biennial. Dry fields, Maine to Penn., near the 

 coast, Illinois and westward : common. 



9. C. horridulum, Michx. (YELLOW THISTLE.) Stem stout (l-4 

 high), webby-haired when young; leaves partly clasping, green, soon smooth, 

 lanceolate, pinnatifid, the short toothed and cut lobes very spiny with yellowish 

 prickles; heads (I'-l^' broad), surrounded at the base by an involucrate whorl of 

 leaf-like and very prickly bracts, which equal or exceed the narrow and unarmed 

 scales of the involucre ; flowers pale yellow or purple. Sandy fields, Massachu- 

 setts to Virginia, and southward, near the coast. 



* * * Outer scales of the appressed involucre barely prickly-pointed: filaments nearly 

 smooth : heads imperfectly dioecious, small and numerous. 



10. C. ARVENSE, Scop. (CANADA THISTLE.) Perennial, the roots exten- 

 sively creeping ; leaves oblong or lanceolate, smooth, or slightly woolly beneath, 

 sinuate-pinnatifid, prickly-margined; flowers rose-purple. Cultivated fields, 

 pastures, and roadsides : common at the North ; a most troublesome weed, ex- 

 tremely difficult to eradicate. (Nat. from Eu.) 



68. CARDTJTJS, Tourn. PLUMELESS THISTLE. 



Bristles of the pappus naked (not plumose), merely rough or denticulate. 

 Otherwise as in Cirsium. (The ancient Latin name.) 



1. C. NtjTANS, L. (MusK THISTLE.) Biennial; leaves decurrent, sinuate, 

 spiny; heads solitary, drooping; flowers purple. Fields near Harrisburg, 

 Pennsylvania, Prof. Porter. (Adv. from Eu.) 



69. ONOPORDON, Vaill. COTTON or SCOTCH THISTLE. 



Heads and flowers nearly as in Cirsium. Scales of the involucre coriaceous, 

 tipped with a lanceolate prickly appendage. Receptacle deeply honeycombed. 

 Achenia 4-angled, wrinkled transversely. Bristles of the pappus numerous, 

 slender, not plumose, united at the base into a horny ring. Coarse, branching 

 annuals, or biennials, with the stems winged by the decurrent base of the lobed 

 and toothed somewhat prickly leaves. Heads large : flowers purple. (The an- 

 cient Greek name of the plant.) 



