coMrosiTAE (composite family) 825 



1. A. AUSTRALE (Loefl. ) Ktze. Sordid-pubescent ; leaves ovate or obovate, 

 1.5-2.5 cm. long, toothed above the middle, and cuneately narrowed at the 

 entire base to a short but slender petiole ; bristly fruits 5, stellate-divaricate, 

 8-10 mm. long. — S. C. to Fla. and La.; extending northw. ^according to 

 Harper) to s. Va. , where presumably of recent introduction ; also sporadically 

 adventive northeastw. (Trop. Am.) 



35. SILPHIUM L. Rosin-weed 



Heads many-flowered ; rays numerous, pistillate and fertile, tbeir broad flat 

 ovaries imbricated in 2-3 rows ; disk-flowers apparently perfect but with entire 

 style and sterile. Bracts of the broad and flattish involucre broad and with 

 loose leaf-like summits, except the innermost, which resemble the linear chaff of 

 the flat receptacle. Achenes broad and flat, dorsally compressed, surrounded 

 by a wing notched at the top, without pappus or with 2 teeth confluent with the 

 winged margins, the achene and its subtending chaff usually falling together ; 

 achenes of the disk sterile and stalk-like. — Coarse and tall perennial herbs, 

 with copious resinous juice, and large corymbose-panicled yellow-flowered heads. 

 (liXcpiov. the ancient name of some resinous plant, transferred by Linnaeus to 

 this genus.) 



* Stern, terete, alternate-leaved ; root very large and thick. 



1. S. laciniatumL. (Rosix-weed, Compass Plaxt.) Bongli-hristly through- 

 out ; stem stout, 1-G.5 m. high, leafy; leaves pinnatehj parted, petioled but 

 dilated and clasping at the base; their divisioiis lanceolate or linear, acute, 

 cut-lohed or pinnatifid, rarely entire ; heads few, 0.5-1 dm. broad, sessile or 

 short-peduncled along the naked summit ; bracts ovate, tapering into long and 

 spreading rigid points ; achenes broadly winged and deeply notched, 1-4 cm. 

 long. — Prairies, Mich, to N. Dak., and south w. July-Sept. — Lower and root- 

 leaves vertical, 3-9 dm. long, ovate in outline, on the wide open prairies dis- 

 posed to present their edges north and south ; hence the name Compass Plant. 



2. S. terebinthinaceum Jacq. (Prairie Dock.) Stem smooth, slender, 1-3 

 m. high, panicled at the summit and bearing several-many large heads, leafless 

 except toward the base ; leaves ovate and ovate-oblong, somewhat heart-shaped, 

 serrate-toothed, thick, rough especially beneath, o-S dm. long, on slender 

 petioles ; scales roundish, obtuse, smooth ; achenes narrowly winged, slightly 

 notched and 2-toothed. Var. pixxatifidum (Ell.) Gray. Leaves deeply cut or 

 pinnatifid. — Prairies and oak-openings, Ont. and O. to Minn., and southw. 

 July-Sept. • 



* * Stem terete or slightly i-angled, leafy j leaves undivided, not large, some 



opposite. 



3. S. trifoliatum L. Stem smooth, often glaucous, rather slender, 1-2 m. 

 high, branched above ; stem-leaves lanceolate, pointed, entire or scarcely serrate, 

 rough, short-petioled, in ichorls ofS or 4, the uppermost opposite ; heads loosely 

 panicled ; achenes rather broadly winged, sharply 2-toothed at the top. — 

 Dry plains and banks, Pa. to s. Ont., and southw. July-Sept. 



4. S. Asteriscus L. Stem hispid, about 1 m. high; leaves opposite, or the 

 loicer rarely in ichorls of 3, the upper alternate, oblong or oval-lanceolate, 

 coarsely toothed, rarely entire, rough-hairy, the lower short-petioled ; heads 

 nearly solitary, large, squarrose ; achenes obovate, winged, 2-toothed, the teeth 

 usually awn-like. — Dry sandy soil, "Md." and Ya. to Mo., and southw. Var. 

 LAEviCAULE DC. Stem nearly or quite smooth. — Va., and southw. 



5. S. integrifblium Michx. Stem smooth or rough, rather stout, 0.5-1.5 m. 

 high, rigid, 4-angular and grooved ; leaves all opposite, rigid, lanceolate-ovate, 

 entire or denticulate, tapering to a sharp point from a roundish h^art-shappd 

 and partly clasping base, rough-pubescent or nearly smooth, thick, 8-12 cm. 

 long ; heads in a close forking corymb, short-peduncled ; achenes broadly winged, 

 deeply notched. — Prairies, Mich, to Minn., Neb., and southw. Aug. 



