Vol.. III.] 



MILKWEED FAMILY. 



II 



17. Asclepias arenaria Torr. Sand Milkweed 



Asclepias 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, i%'-2>' wide, 

 the angle of the primary nervation broad; um- 

 bels densely many-flowered, short-peduncled or 

 sessile; corolla greenish- white, its segments 

 oval-oblong, 4 // ~5 // 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 abruptly incurved subulate apex; follicles 

 puberulent, 4 / -5 / long, erect on the decurved 

 fruiting pedicels. 



T On sand-bars and hills along rivers, Nebraska and 

 Colorado to Mexico and New Mexico. June-Sept. 



18. Asclepias ovalifolia Dec. Oval- 

 leaved Milkwort. (Fig. 2917.) 



Asclepias ovalifolia Dec. in DC. Prodr. 8: 567. 1844. 

 Finely tomentose all over; stem simple, usually 

 slender, erect, io'-2 high. Leaves oval, ovate, 

 oblong or ovate-lanceolate, acute or obtuse and 

 mucronulate at the apex, rounded or narrowed at 

 the base, 2 / -3 / long, y 2 '-\%.' wide, short-petioled, 

 the upper surfaces becoming glabrate at maturity; 

 umbels solitary or few, many-flowered; peduncles 

 short; corolla greenish- white or purplish, its seg- 

 ments ovate-oblong, obtuse, 2 // ~3 // long; column 

 very short; hoods oval-oblong, nearly twice as 

 long as the anthers, bearing a large acute tooth on 

 each of the inner margins; horn subulate, in- 

 curved over the stigma; follicles ascending on the 

 reflexed fruiting pedicels, pubescent. 



In woods and on prairies, Illinois to Minnesota, 

 Manitoba and the Northwest Territory. June-July. 



19. Asclepias brachystephana Engelm. 

 Short-crowned Milkweed. (Fig. 2918.) 



Asclepias brachystephana Engelm.; Torr. Bot. Mex. 

 Bound. Surv. 163. 1859. 



Puberulent when young, soon glabrate; stems 

 clustered, often branched, spreading or ascend- 

 ing, 6'-i2 / long. Leaves mostly opposite, lance- 

 olate or linear-lanceolate, thick, long-acuminate 

 at the apex, rounded, subcordate or narrowed at 

 the base, 2 / ~5 / long, 2 // -6 // wide, or the lowest 

 shorter; petioles i // -4 // long; umbels several, ter- 

 minal and axillary, few-flowered; peduncles short; 

 pedicels densely woolly, equalling or longer than 

 the peduncles; corolla greenish-purple, its seg- 

 ments about 1" long; column very short or none; 

 hoods ovate, obtuse, shorter than the anthers, the 

 short erect-incurved horn slightly exserted; fol- 

 licles erect on the spreading or decurved fruiting 

 pedicels, downy or hoary, acuminate, 2 / ~3^ / long. 



In dry soil, Kansas (according to B. B. Smyth), 

 Wyoming to Texas, Arizona and Mexico. June-Aug. 



