ASCLEPIADACEAE. 



VOL. III. 



16. Asclepias syriaca L. Common Milk- 

 weed. Silkweed. Fig. 3398. 



Asclepias syriaca L. Sp. PI. 214. 1753. 



Asclepias Cornuti Dec. in DC. Prodr. 8: 564. 1844. 



Stem stout, usually simple, 3-5 high, finely 

 pubescent at least above. Leaves oblong, oval or 

 ovate, finely and densely pubescent beneath, soon 

 glabrous above, acute or obtuse and cuspidate at 

 the apex, obtuse, narrowed or subcordate at 

 the base, 4'-g' long, 2'-$' wide, the primary nerves 

 wide-spreading; petioles stout, 3"-8" long; umbels 

 several or numerous ; peduncles pubescent or tomen- 

 tose, 1 4 '-3 4' long; pedicels i'-2' long; corolla green- 

 purple or greenish-white, its segments oblong-lan- 

 ceolate, 3"-4" long; column short and thick, the 

 hoods ovate-lanceolate with a tooth on each side, 

 longer than the anthers and the incurved horn ; fol- 

 licles 3'-s' long, erect on recurved pedicels, tomen- 

 tose and covered with short soft processes. 



In fields and waste* places, New Brunswick to Sas- 

 katchewan, North Carolina and Kansas. Leaves rarely 

 lanceolate. Silky swallow-wort. Virginia silk. Wild 

 cotton. June-Aug. 



Asclepias kansana Vail, of Kansas, differs by erect-spreading hoods of the corolla and more 

 densely tomentose follicles. 



17. Asclepias speciosa Torr. Showy Milk- 

 weed. Fig. 3399. 



Asclepias speciosa Torr. Ann. Lye. N. Y. 2 : 218. 1826. 

 A. Douglasii Hook. Fl. Bor. Am. 2: 53. pi. 152. 1834. 



White-tomentose or canescent all over, or gla- 

 brate below, pale; stem simple, stout, i-2i high. 

 Leaves thick, broadly ovate or oval, obtuse and cus- 

 pidate or acute at the apex, subcordate, rounded or 

 narrowed at the base, petioled, 3'-8' long, 2'-4' wide; 

 peduncles i'-3' long; umbels several or rarely soli- 

 tary, many-flowered; pedicels stout, p"-i8" long; 

 corolla purple-green, its segments oblong or ovate- 

 oblong, 4"-6" long, tomentose on the outer face ; 

 column very short or none; hoods lanceolate, S"-7" 

 long, obtusish, expanded and with 2 blunt teeth be- 

 low, the apex ligulate, 5-7 times as long as the 

 anthers ; horn short, inflexed ; follicles erect f or 

 spreading on the recurved fruiting pedicels, 3'~4' 

 long, densely woolly and covered with soft spinose 

 processes. 



In moist soil, Minnesota to British Columbia, south 

 to Kansas. Utah and California. May-July. 



1 8. Asclepias arenaria Torr. Sand Milk- 

 weed. Fig. 3400. 



A. arenaria Torr. Bot. Mex. Bound. Surv. 162. 1859. 



Densely tomentose-canescent all over, stems 

 simple, ascending or erect, stout, i-2 high. 

 Leaves obovate or oval, wavy-margined, thick, 

 obtuse or retuse and cuspidate at the apex, trun- 

 cate, subcordate, obtuse, or rarely some of them 

 narrowed at the base, 2'-4' long, ii'-3' wide, the 

 angle of the primary nervation broad ; umbels 

 densely many-flowered, short-peduncled or ses- 

 sile ; corolla greenish-white, its segments oval- 

 oblong, 4"-S" long; column i"-2" high; hoods 

 oblong, truncate at each end, oblique at the apex, 

 longer than the anthers, with a broad tooth on 

 each side within ; horn semi-lunate with an ab- 

 ruptly incurved subulate apex; follicles puberu- 

 lent, 4'-$' long, erect on the decurved fruiting 

 pedicels. 



On sand-bars and hills along rivers, Nebraska and 

 Colorado to Mexico and New Mexico. June-Sept. 



