GENUS 49. THISTLE FAMILY. 459 
About 35 species, natives of the warmer parts of America. Besides the following, 2 or 3 others 
occur in the southwestern United States. Type species: Melampodium americanum L. 
1. Melampodium leucanthum T. & G. 
Plains Melampodium. Fig. 4419. 
ey eer leucanthum T. & G. Fl. N. A. 2: 271. 
1842, ‘ 
Perennial, woody at the base, branched, .canes- 
cent, 4-12’ high, the branches slender. Leaves 
linear, lanceolate, or the lower spatulate, sessile, 
entire, or nearly so, canescent, 1-2’ long, 13-3” 
wide, obtuse or obtusish at the apex; heads 4’-2’ 
broad, terminating the branches; peduncles slen- 
der, 1-3’ long; outer bracts of the involucre ovate 
or oval, obtuse, united below; rays 5-09, cuneate- 
oblong, white, 2-3-lobed, firm in texture, veiny, 
persistent; inner bracts turbinate or terete, hood- 
éd, muricate, the hood wider than the body. 
In dry soil, Kansas to Colorado, Arizona, Texas 
and Mexico. June-Oct. Not distinguished, in our 
first edition, from M, cinereum DC. of Texas and 
northern Mexico. 
50. ACANTHOSPERMUM Schrank, Pl. Rar. Hort. Monac. pl. 53. 1819. 
Annual rather coarse herbs, with pubescent foliage and erect or creeping stems, opposite, 
broad, often leathery, toothed leaves, and radiate but inconspicuous heads, axillary to leaf- 
like bracts. Involucre double, an outer one of flat herbaceous bracts, and an inner one of 
several smaller bracts which become bur-like and fall away enclosing an achene at maturity. 
Receptacle concave or convex. Ray-flowers few, in 1 series, the rays very small, yellowish, 
concave or hooded. Disk-flowers perfect, sterile. Anthers entire at the base. Achenes 
broadest above the middle, slightly curved. Pappus wanting. [Greek, thorn-seed, from the 
prickly, bur-like fruits.] 
About 3 species, natives of tropical America. Type species: Acanthospermum brasilium Schrank. 
Sy 
1. Acanthospermum australe (Loefl.) Kuntze. 
Spiny-bur. Fig. 4420. 
Melampodium australe Loefl. Iter. Hisp. 268. 1758. 
A. xanthoides DC. Prodr. 5: 521. 1836. 
A, australe Kuntze, Rev. Gen. Pl. 303. 1891. 
Stems branching at the base, the branches prostrate or 
creeping, 3°-2° long. Leaves ovate, oval or rhombic, 4’-1’ 
long, usually acute, serrate-dentate above the middle, cu- 
neate at the base; peduncles shorter than the subtending 
leaves; involucre campanulate, the bracts broadly ovate, 
obtuse, 1-14” long, uniformly prickly; disk-flowers with 
corollas 1” long, puberulent; mature inner bracts of the 
involucre forming a starfish-like bur, each lobe 4’-5” long, 
densely beset with uniform blunt weak prickles. 
In waste places and dry soil, Virginia to Florida and Louisi- 
ana. June-Oct. Widely distributed as a weed in tropical re- 
gions. 
51. SILPHIUM L. Sp. Pl. 919. 1753. 
Tall perennial herbs, with resinous juice, opposite whorled or alternate leaves, and large 
corymbose or paniculate (rarely solitary) peduncled heads of both tubular and radiate yellow 
flowers. Involucre hemispheric or campanulate, its bracts imbricated in few series. Recep- 
tacle flat or nearly so, chaffy, the chaff subtending the disk-flowers. Ray-flowers in 2 or 3 
