210 
++ Leaves many of them alternate, all once or twice pinnatifid. 
4. A. artemisiefolia L. (RoMAN WORMWOOD. HO0G-WEED. BITTER-WEED.) 
Much branched, 3 to 9 dm. high, hairy or roughish-pubescent: leaves thin, twice- 
pinnatifid, smoothish above, paler or hoary beneath: fruit obovoid or globular, armed 
with about 6 short acute teeth or spines,—A common weed of waste grounds. Ex- 
tremely variable. 
5. A. psilostachya DC. Paniculate-branched, 6 to 15 dm. high, rough and some- 
what hoary with short hispid hairs: leaves once-pinnatifid, thickish, the lobes acute, 
those of the lower leaves often incised: fruit obovoid, without tubercles or with very 
small ones, pubescent.—Moist prairies and beds of streams, central and western 
Texas. 
50. FRANSERIA Cav. 
Herbs or shrubby plants, with chiefly alternate leaves, male heads as 
in Ambrosia (or sometimes intermixed with the female), fertile involucre 
1 to 4-tlowered, 1 to 4-celled (a single pistil to each cell), 1 to 4-beaked, 
more or less bur-like (being armed over the surface with several prickles 
or spines in more than one series), turgid achenes, and no pappus. 
1. F. tenuifolia Gray. Herbaceous, erect, 3 to 15 dm. high, leafy to the top, his- 
pid, variously pubescent, or glabrate: leaves mostly 2 or 3-pinnately parted or dis- 
sected into narrowly oblong or linear lobes, and the narrow primary rhachis often 
with some interposed small lobes, the terminal elongated: fruiting involucre seldom 
over 2mm. long (1 or 2-flowered), armed with 6 to 18 short and stout incurving 
spines with tips almost always hooked.—Moist grounds, southern and western 
Texas. 
2. F. Hookeriana Nutt. Herbaceous and low, diffusely spreading, freely 
branched, hirsute-pubescent or hispid, sometimes canescent when young: leaves of 
ovate or roundish outline, bipinnatifid, or the upper oblong and pinnatifid: fruit- 
ing involucre 6 to 8 mm. long (1-flowered), armed with flat and thin long and 
straight spines.—Plains and along streams, western Texas. 
51. XANTHIUM Tourn. (COCKLEBUR. CLOTBUR.) 
Coarse weeds, with low and branching stout stems, alternate toothed 
or lobed petioled leaves, sterile and fertile flowers in different heads 
(the latter clustered below, the former in short spikes or racemes 
above), sterile involucres and flowers as in Ambrosia, but the bracts 
separate and the receptacle cylindrical, fertile involucre closed, coria- 
ccous, clothed with hooked prickles (so as to form a rough bur), 2- 
-clled and 2-flowered, oblong flat achenes, and no pappus. 
* Leaves attenuate to both ends, with triple spines at the base. 
1. X. spinosum L. (SPINY CLOTBUR.) Hoary-pubescent: stems slender, with 
slender yellow 3-parted spines at the axils: leaves lanceolate, or oblong-lanceolate, 
tapering to a short petiole, white-downy beneath, often 2 or 3-lobed or cut: fruit 8 
mm. long, pointed with a single short beak,—A tropical American weed, introduced 
into eastern and southern Texas. 
* * Leaves cordate or ovate, 3-nerved, dentate and often lobed, long-petiolate: axils un- 
armed : fruit 2-beaked. 
2, X. Strumarium L. Low, 3 to 6 dm. high: fruit 12 to16 mm, long, glabrous or 
puberulent, with usually straight beaks and rather slender spines.—A common 
weed of cultivated grounds. 
