690 MISC. PUBLICATION 42 3, U. S. DEPT. OF AGRICULTURE 



usually with a hornlike internal crest; pods ovoid, lanceolate, or 

 fusiform. 



A. galioides and perhaps other species contain a glucoside that is 

 poisonous to livestock, especially to sheep, but the plants are seldom 

 eaten. Appreciable quantities of rubber are found in the sap of some 

 of the Arizona species. The Hopi Indians are reported to cook the 

 young shoots and leaves of A. speciosa with meat. A. galioides is 

 considered by the Hopi to increase the flow of milk in women. Milk- 

 weeds contain a substance, asclepain, which can be used as a substitute 

 for papain for tenderizing meat. 



Key to the species 



1. Stems naked or nearly so (the leaves soon deciduous), rushlike, glaucous, more 

 or less puberulent above; pods fusiform (2). 

 2. Stems usually 10 or fewer, 10 mm. or more in diameter at base, decidedly 

 woody below; corolla lobes 5 to 6 mm. long, white tinged with purple; 

 hoods shorter than the anthers, spreading, not dilated at apex. 



1. A. ALBICANS. 



2. Stems usually 20 or more, less than 10 mm. in diameter at base, not notice- 



ably woody above the caudex; corolla lobes 7 to 8 mm. long, pale green; 

 hoods at least twice as long as the anthers, erect, dilated at apex. 



2. A. SUBULATA. 



1. Stems leafy, not rushlike, the leaves persistent (3). 



3. Corolla lobes orange or scarlet; stems villous or hirsute; leaves very numer- 



ous, linear- to oblong-lanceolate 3. A. tuberosa. 



3. Corolla lobes whitish, greenish, or purplish; stems not villous or hirsute, 

 except in A. lemmoni (4). 

 4. Leaf blades seldom more than 15 mm. wide, ovate-lanceolate or narrower, 

 usually more than 3 times as long as wide (5). 

 5. Fruiting pedicels normally erect or ascending and straight, but some- 

 times sigmoid-curved; leaf blades linear or linear-lanceolate, not 

 more than 5 mm. wide; pods fusiform; column about 1 mm. long (6). 

 6. Hoods oblong-ovate, conspicuously surpassing the anthers; leaves 

 distinctly short-petioled, rather flaccid, mostly in pairs; corolla 

 pinkish white 4. A. linifolia. 



6. Hoods broadly ovate, not^ or but slightly surpassing the anthers; 



leaves sessile or subsessile, not flaccid, mostly in whorls of 3 or 4; 



corolla greenish white 5. A. galioides. 



5. Fruiting pedicels deflexed or decurved (7). 



7. Plant sufFrutescent, puberulent; leaf blades narrowly linear or almost 



filiform, with more or less revolute margins (8). 

 8. Hoods with long, subulate, recurved, hispidulous tips; leaves oppo- 

 site, not crowded or rigid; umbels seldom more than 5-flowered; 

 pods fusiform 6. A. macrotis. 



8. Hoods not subulate-attenuate; leaves alternate or falsely verticil- 



late, crowded, rather rigid; umbels usually more than 10- 

 flowered; pods ovate-lanceolate to broadly ovate in outline. 



7. A. LINARIA. 



7. Plant herbaceous above the caudex (9). 



9. Hoods conspicuously dentate at the truncate apex; plant obscurely 



puberulent or glabrate; leaf blades narrowly linear, not more 

 than 4 mm. wide; corolla lobes pale green; pods fusiform, about 



10 cm. long 8. A. quinquedentata. 



9. Hoods not conspicuously dentate at apex; plant more or less 



floccose-tomentose, at least on the young parts; leaf blades 



linear to lanceolate; corolla lobes usually purple or purplish; 



pods ovate to lance-ovate in outline, considerably less than 



10 cm. long (10). 



10. Leaf blades at most obscurely ciliolate; umbels mostly lateral, 



few-flowered; hoods shorter than to equaling the anthers (11). 



11. Leaf blades lanceolate, the lower ones 6 to 15 mm. wade near 



the base; umbels distinctly stalked; hoods much shorter 



than the anthers, strongly angulate-toothed in front; pods 



conspicuously longitudinally striate with darker-colored 



stripes .__ 9. A. brachystephana. 



