裸穗豬草

Ambrosia psilostachya DC. Prodr. 5: 526. 1S36
Ambrosia Lindheimeriana Scheele, Linnaea 22: 156. 1849.
Ambrosia coronopifolia var. [asperula, &c] A. Gray, Bost. Jour. Nat. Hist. 6: 226. 1850. Ambrosia psilostachya Lindheimeriana Blankinship, Rep. Mo. Bot. Gard. 18: 173. 1907. Ambrosia psilostachya asperula (A. Gray) Blankinship, MS.
A perennial herb, with a creeping rootstock; stem 3-6 dm. high, branched above, striate,
hirsutulous with short ascending hairs; leaves subsessi'.e, lanceolate in outline, pinna tifid,
scabrous-hirsutulous and glandular-granuliferous, the hairs with pustulate bases; divisions
linear-lanceolate, acute or acuminate, entire or the lower few-toothed; staminate heads numerous, terminating the branches; involucre oblique, broadly obconic, about 2.5 mm. broad, crenate on the margins, hispidulous, the hairs short, with conspicuous pustulate bases; pistillate heads solitary or 2 or 3 together in the axils of the upper leaves; body of the fruit 2.5 mm. long, obovoid, rugose, hirsutulous; beak nearly 1 mm. long; tubercles 4-6, very short but acute.
Type locality: Between San Fernando and Matamoros, Tamaulipas. Distribution: Louisiana to New Mexico and Tamaulipas.

Ambrosia californica Rydberg, sp. nov
Ambrosia psilostachya A. Gray, Bot. Calif. 1: 344, in part. 1876.
A perennial herb, with a creeping rootstock; stem 3-10 dm. high, hirsute or pilose, with spreading hairs; leaves subsessile, pinnatifid, long-strigose and somewhat glandular-granuliferous on both sides; leaf-blades ovate in outline; segments linear-lanceolate or lanceolate in outline, acute, and entire, toothed, or incised; staminate heads numerous, in racemes at the ends of the branches; involucre broadly turbinate, shorter than the flowers, 3-4 mm. broad, pilose, usually dark-colored; paleae of the receptacle filiform; corollas puberulent; pistillate heads in the upper axils; body of the fruit elongate-obovoid, glandular-puberulent and slightly pilose towards the end, somewhat reticulate; beak fully 0.5 mm. long; spines 4-7, short, conic, acute.
Type collected at Santa Barbara, California, 1865, Torrey 226 (herb. N. Y. Bot. Gard. and Columbia Univ.).
Distribution: California, from Cape Mendocino south, and Humbolt County, Nevada.

Ambrosia rugelii Rydberg, sp. nov
An annual herb, with branched roots; stems 3-6 dm. high, densely hirsute, with spreading
hairs; leaves 5-8 cm. long, petioled, pinnately divided, dark-green, when dried almost black,
hispidulous on both sides, thick and strongly veined; petioles very short or those of the upper
leaves none; blades ovate in outline; segments oblong, acute, toothed; staminate heads usually
numerous, in racemes terminating the branches; involucre 5-lobed and crenate, 3-3.5 mm.
broad, hispidulous; paleae of the receptacle filiform; corolla puberulent; pistillate heads few,
in small clusters in the axils of the upper leaves; body of the fruit 2.5-3 mm. long, puberulent;
beak less than 1 mm. long; spines 5-6, sharp, conic-subulate, 0.3-4.0 mm. long.
Type collected in Florida, 1845, Rugel 508 (herb. N. Y. Bot. Gard.; cotype, U. S. Nat. Herb.). Distribution: Florida and Georgia.