224 AMBROSIACEAE 



4. DICORIA T. & G. 



Upper leaf-blades broadly spatulate. ovate, or roundish. 



Inner bracts 10-15 mm. long; achenes with pectinate margins. 1. D. Wetherillii, 



Inner bracts 6-8 mm. long: achenes with continuous erose margins. 2. D. canescens. 

 Leaves all oblong-lanceolate to linear. 



Fertile flowers soUtary in the heads: teeth of the achenes connected by a scarious 

 margin. 3. D. Brandegei. 



Fertile flowers 2 in each head ; achenes without scarious margins. 4. D. panicuiata. 



5. HYMENOCLEA T. & G. l. H. Salsola. 



6. AMBROSIA (Tourn.) L. Ragweed, Roman Wormwood, Bittek-weed. 



Involucres of the staminate heads 3-ribbed; leaves palmately 3-S-cleft or entire. 



1. A. trifida. 

 Involucres of the staminate heads not ribbed: leaves once to thrice pinnatifld. 

 Annual; fruit with acute teeth. 



Leaves thin, not strongly veined, bipinnatifld. 2. A. elatior. 



Leaves thick, strongly veined, pinnate with broad toothed or cleQt segments. 



3. A. media 

 Perennial with rootstock ; fruit with unarmed or blunt tubercles. 4. A. psilostachua. 



7. FRANSERIA Cav. 

 Fruit not villous. 



Spines of the fruit flat, never hooked. 



Plant shrubby; leaves silvery white; pistillate heads mostly 2-flowered and 2- 



beaked. ]. F. albicaulis. 



Plant annual; leaves strigose, not white: pistillate heads 1-flowered and 1-beaked. 

 Leaves bi- or tri-pinnatifld. 2. F. acanOwcarpa. 



Leaves pinnately 3-5-cleft. 3. F. rhontana. 



Spines terete, usually more or less curved. 



Bur 1-beaked, 1-2-flowered: leaves not %)mentose beneath. 



Annual; divisions of the leaves oblong or linear-oblong, acute. 



4. F. tenuifolia. 

 Perennial with a suffrutescent base; leaf -segments linear, obtuse. 



5. F. linearis. 

 Bur 2-beaked, 2-flowered; leaves tomentose beneath; plants perennial with a 



rootstock. 

 Leaves interruptedly pinnatifld, with lobed or coarsely toothed divisions. 



6. F. discolor. 

 Leaves pinnately 3-5-parted or entire; divisions or blades merely serrulate or 



entire. 7. F. tomentosa. 



Fruit villous: plant shrubby. 8. F. friocenlra. 



8. XANTHIUM L. Cocklebur; Clotbur. 



Spines of the fruit about 20. 1. X. oligocanthum. 



Spines of the fruit 50-200. 



Bur and its spines merely puberulent or glandular, only slightly if at all hispid. 



2. X. pennsylvanicum. 

 Bur and especially its numerous spines very hispid as well as glandular. 



Prickles of the bur very numerous and dense, brownish-pubescent. 



3. X. echinatum. 

 Prickles of the bur fewer, scattered, yellowish-pubescent. 



Body of the bur oval or ovate, not twice as long as broad. 



4. X. glanduliferum. 

 Body of the bur oblong, twice as long as thick, densely spiny. 



Bur about 2 cm. long; spines not longer than the width of the body. 



5. X. commune. 

 Bur 2.5-3 cm. long; spines much longer than the width of the body. 



6. X. spcciosum. 



Family 134. CARDUACEAE, Thistle Family. 



Anther-sacs not tailed at the base. 



Stigmatic lines at the base of the style-branches or below the middle; heads always 

 discoid, never yellow or brown. 

 Style-branches flUform or subulate, hispidulous. Tribe 1. VERNOXIEAE. 

 Style-branches more or less clavate, papillose-puberulent. 



Tribe 2. EUPATORIEAE. 

 Stigmatic Unes extending to the tips of the style-branches or to the appendage thereof, 

 if present; heads most commonly radiate and with yellow or brown disk-flow- 

 ers. 

 Style-branches of the perfect flowers with more or less distinct appendages, these 

 usually strongly hairy outside, glabrous inside, but never with a ring of longer 

 hairs. • Tribe 3. ASTEREAE. 



Style-branches of the perfect flowers without appendages, or if with appendages, 

 these hairy on both sides and with a ring of longer hairs. 

 Pappvis never capillary; style-branches rarely appendaged. 

 Bracts of the involucres herbaceous or foliaceous. 



