ASCLEPIADACEAE 941 



purple line : follicles erect on reflexed fruiting pedicels, about 8 cm. long, obliquely fusiform, 

 glabrous : seeds 6 mm. long, very thin : coma 2 cm. long. 



In rocky ground and on prairies, Nebraska and Colorado to New Mexico and Texas. Summer. 



4. Acerates angustifolia (Nutt. ) Decne. Plants nearly glabrous in age. Stems 

 mostly several from the same tuberous rootstock, straight, 3-6 dm. high, clothed with a 

 minute, mostly retrorse puberulence, becoming glabrate below : leaves alternate, scattered 

 or some of the lower ones opposite ; blades sessile, narrowly linear, 5-12 cm. long or longer, 

 glabrous, the revolute margins and thick midrib scabrous beneath : umbels small, 10-15- 

 flowered, lateral, 7-13, or more, on the same stem : pedicels 7-10 mm. long, minutely pu- 

 bescent with spreading or retrorse hairs : corolla-lobes 5 mm. long, oblong, greenish : hoods 

 white, attached over the whole of the short column, erect, as high as the short anthers, later- 

 ally compressed, 3-dentate at the apex, the acute central tooth merely a prolongation of the 

 thickened crest-like midrib and much shorter than the erect obtuse lateral ones, each inner 

 margin spreading into an erosely truncate lobe which usually overlaps that of the next hood 

 and terminates in an interior ring of five 2-lobed minute processes or appendages between 

 the anthers : anther-wings salient and conspicuously auriculately notched slightly below the 

 middle, narrowed at the base : follicles slender-fusiform, straight, erect on erect fruiting pedi- 

 cels, about 8 cm. long, minutely pubescent : seeds about 5 mm. long, thin : coma 3 cm. long. 



On dry sandy prairies, Nebraska and Colorado to Texas. Summer and fall. 



5. ASCLEFIAS L. 



Herbs from deep perennial roots, sometimes woody at the base. Stems solitary or 

 clustered, erect or decumbent, simple or branched. Leaves opposite, alternate or whorled. 

 Inflorescence umbelliform, terminal or axillary, from few- to many-flowered. Calyx small, 

 with commonly few to many minute glands at the base of the lobes. Corolla rotate, deeply 

 5-parted : lobes dextrorsely valvate-convolute in bud, reflexed in anthesis. Hoods of the 

 crown involute, complicate, arising from the base of the corolla-lobes or raised on a column 

 which is shorter than the anthers, erect, eoncave-cucullate, bearing an acute or rarely ob- 

 tuse horn or tooth-like process projecting from the base or summit within, and sometimes 

 with minute accessory processes alternating between the anthers. Anther-wings corneous, 

 commonly widening toward the salient usually triangular base, which is truncate, semi- 

 hastate, not rarely rounded, entire or auriculate-notched, sometimes salient at the middle. 

 Stigma 5-angular, flat-topped. Caudicles very slender. Follicles naked, or in few species 

 warty or echinate with soft processes. Coma of the seed mostly present. MILKWEED. 



A. Hoods sessile, broader or at least not attenuate and stalked at base : horn variously inserted, con- 

 spicuous and usually exserted : anther-wings broadest and salient at base. 

 Follicles erect on deflexed fruiting pedicels. 



Hoods oblong or dorsally hastate-lanceolate, acute. 

 Corolla and hoods orange-yellow. 



Hoods linear-oblong or linear-lanceolate, the interior folds meeting the margins near the 



apex : calyx-lobes barely % as long as the corolla-lobes. 



Leaf-blades oblong, obtuse : follicles slender-fusiform. 1. A. decumbent. 



Leaf-blades lanceolate-oblong or linear-lanceolate, acute or rarely 



obtuse: follicles fusiform. 2. A. tuberosa. 



Hoods broadly oblong, the interior folds vanishing remote from the 



apex : calyx-lobes nearly % as long as the corolla-lobes. 2a. A. Solfsii. 



Corolla and hoods white or yellowish green : anther-wings angled above 



the base. 3. A. Curtissii. 



Hoods not conspicuously hastate-lanceolate on the back. 



a. Leaf-blades large and broad ; primary veins transversely spreading 



(except in A. exaltata). 

 * Leaf-blades sessile or subcordate at base. 



Leaf-blades broader than long : umbels typically all lateral. 4. A. latifolia. 



Leaf-blades longer than broad. 



Leaf-blades oblong or elliptic, wavy-margined : umbel long-pe- 



duncled, typically solitary. 5. A. amplexicaulis. 



Leaf-blades ovate, succulent, ultimately reddish veined : umbels 



several. 6. A. humistrata. 



** Leaf-blades petioled, tomentose or pubescent, 

 f Flowers pinkish purple or dark purple. 



Leaf-blades typically oblong, commonly obtuse : umbels numer- 

 ous : hoods not exceeding the anthers. 7. A. Syriaca. 

 Leaf-blades typically ovate-oblong, acutish : umbels solitary or 



few : hoods exceeding the anthers. 8. A. purpurascens. 



ff Flowers greenish : hoods yellowish. 



Leaf-blades oblong-elliptic, acute or acutish at each end : umbels 



numerous, lateral. 9. A. tomentosa. 



Leaf-blades oblanceolate, obtuse, tapering at the base. 10. A. aceratoides. 



*** Leaf-blades petioled, glabrous or nearly so : flowers white or tinged 

 with greenish purple. 



