Acanthospermum. COMPOSIT.E. 239 



others conspicuous. — Gfertn. Fruct. t. 1G9; R. Br. in Linn. Trans, xii. 104; 

 DC. Prodr. v. 517; Benth. & Hook. Gen. ii. 349, 



* Perennial and the base slightly lignescent : akene with apex exposed at the hooded orifice of 

 the fructiferous bract: rays plane, conspicuously exserted, comparatively ample, tardily decidu- 

 ous from the akene, white! 



M. cinereum, UC. Branched from the base, a span to a foot liigli, rather slender, cinere- 

 ous or even silvery-canescent with a fine and mostly close pubescence, or greener and be- 

 coming strigulose : leaves linear or the lower lanceolate or spatulate, entire or undulate, or 

 even siuuate-pinnatifid : peduncles slender : ligules 5 to 9, cimeate-obloug, 2-3-lobed at apex, 

 3 to 6 lines long : bracts of tlie involucre ovate, appressed, sliglitly united at base : fruc- 

 tiferous bracts (2 lines long, including tlie hood) turbinate, nearly terete, somewhat incurved, 

 muricate with sliarp tubercles ; its hood about the length of the body and very much wider, 

 imperfectly cupuliform, nearly smooth, callous-thickened or becoming suberose, its truncate 

 and usually even margin commonly incurved. — Prodr. v. 518 (excl. habitat) ; Gray, PI. 

 Fendl. 78, PI. Wright., &c. M. leucanthum, Torr. & Gray, Fl. ii. 271. — Open ground, W. 

 Arkansas and Texas to Arizona. (Adj. Mex.) 



Var. ramosissimum. (M. ramosissimum, DC. 1. c. by the char., but habitat and 

 number of distribution of this and of M. cinereu7n were interchanged in the Prodromus!) 

 More loosely pubescent and diffusely branching : heads mostly smaller : hood of the fruc- 

 tiferous bracts with the less thickened margin little or not at all involute, sometimes erose 

 or denticulate and bearing a inucro or short (seldom "uncinate") cusp. — Southern borders 

 of Texas, BerhuuUer, Palmer. (vVdj. Mex.) 



* * Annuals, commonly low, erect, branching, with linear or oblong mostly entire leaves: akene 

 with merely the apex exposed at the summit of the enclosing fructiferous bract : ray and disk- 

 corollas yellow. Our species all quite alike in foliage and habit. 



M. hispidum, HBK. Hispidulons-hirsute, sometimes a foot high: rays very small, barely 

 a line long • outer involucral bracts oval, distinct to the base; fructiferous bracts truncate 

 and not at all appendaged at the somewhat oblique summit, more or less tuberculate on the 

 back and sides. — Nov. Gen. & Spec. iv. 273, t. 399; DC. 1. c. 520; Gray, PI. Wright, ii. 85. 

 — 8. Arizona, Wrifjld, Lemmon. (Mex.) 



M. CUpulatum, Gray. Somewhat hispidulous-pubescent : rays small but exserted, 2 lines 

 long : outer involucral bracts connate to above the middle into an obtusely 5-lobed hemi- 

 spherical or saucer-shaped cup : fructiferous bracts nearly of the preceding. — Proc. Am. 

 Acad. viii. 291. — Borders of S. Arizona, on the Mexican side, Sdiott. (Mex.) 



M. longicornu, Gray. Sparsely hispidulous : rays exserted, oblong, when well devel- 

 oped 3 lines in length and as long as the involucre, the outer bracts of which are distinct : 

 fructiferous bracts more uervose, little tuberculate or smooth, the summit cupulately pro- 

 duced and gradually extended exteriorly into a circinnate or revolute horn or rigid awn, 

 fully as long as the body, longer and more attenuate than in M. scriceum, and sericeous- 

 pubescent along the outside. — Mem. Amer. Acad. (PL Thurb.) v. 321, & Bot. Mex. Bound. 

 85. — fi. Arizona,, Thurher, Schott. (Adj. Mex.) 



69. ACANTHOSPERMUM, Schrank. ("AKav6a, a prickle or thorn, 

 and (TTrepfxa, seed, i. e. prickly-fruited.) — Homely annual weeds, much branched 

 from the base ; with opposite dentate leaves, in their axils and in the forks small 

 subsessile or short-peduncled heads of yellowish flowers ; the (4 to 7) bur-like 

 involucral bracts enlarging in age. Natives of the tropics, one or two species 

 becoming naturalized. — PI. Rar. Hort. Monac. t. 53; DC. Prodr. v. 521. Cen- 

 trospermum, HBK. Nov. Gen. & Spec. iv. 270, t. 397. « 



A. xaxthioi'des, DC. 1. c. Diffusely procumbent or creeping: stems pubescent: leaves 

 small (a1>out inch long), mostly obovate, narrowed at base into a short petiole : fructiferous 

 involucral bracts narrowly oblong, longitudinally sulcate, truncate, thickly beset especially 

 along the angles with uniform and small hooked prickles. — A. Brasibnn, Schi-ank, I.e."? 

 a hirsute form. Melamjjodiiim austnile, Ltt'fl., L. Centrosperminn xanthioides, HBK. 1. c. — 

 Roadsides and waste grounds, S. Carolina to Florida, &c. (Nat. from S. Amer.) 



