270 ASCLEPIADACEAE. 



Family no. ASCLEPIADACEAE Lindl. Milkweed Family. 



Corolla-lobes reflexed during anthesis. 



Hoods of the crown crestless within or with an obscure crest-like midrib. 



i. ACERATES. 



Hoods of the crown each with a horn-like process within. 2. Asclepias. 

 Corolla-lobes erect-spreading during anthesis ; hoods with a crest at least above. 



3. ASCLEPIODOEA. 



I. ACERATES Ell. Green Milkweed. 



Auricles of the hood, when present, concealed within ; leaves oval to linear- 

 lanceolate. I. A. viridiAora. 

 Auricles of the hoods conspicuously spreading ; umbels lateral ; leaves narrowly 

 linear. 

 Hoods eraarginate or truncate at the summit, crestless within ; umbels dis- 

 tinctly peduncled. a. A, auriculata. 

 Hoods trilobed at the summit with an internal crest-like midrib terminating in 

 the middle lobe ; umbels subsessile or on very short peduncles. 



3. A. angusiifolia. 



1. Acetates viridiflora (Raf.) Eat. In dry or sandy soil from Mass. and 

 Mont, to Fla. and N. M. — Alt. 4000-6000 ft. — Fossil Creek, Larimer Co.; 

 Horsetooth Mountain; Boulder; Berkeley; Valverde. 



:i. Acerates auriculata Engelm, On dry plains from Neb. and Colo, to 

 Tex. and N. M. — Alt. 4000-5000 ft. — Caiion City; Ft. Collins; Horsetooth 

 Gulch; Denver; Valverde; Montclair. 



3. Acerates angustifolia (Nutt.) Decaisne. {Asclepias stenophylla A. 

 Gray) In sandy soil from S. D. and Colo, to Mo., Tex. and N. M. — Exact 

 locality not given. 



2. ASCLEPIAS L. Milkweed, Silkweed. 



Leaves orbicular to linear-lanceolate, opposite. 



Follicles with soft spinulose processes, tomentose ; leaves large and broad, 



tomentose, transversely veined, oval or ovate. 1. A. speciosa. 



Follicles without processes. 



Flowers very large ; petals over i cm. long ; column none ; horns included in 

 the hoods ; leaves almost orbicular, subcordate at the base. 



2. A. cryptoceras. 

 Flowers middle-sized or small ; petals much less than i cm. long ; column 



usually present and horns exserted. 

 Leaves broadly oval or rectangular oval or nearly orbicular, obtuse or 

 retuse at both ends ; umbels sessile. 

 Plant puberulent when young, glabrate in age ; column very short. 



3. A. latifolia. 

 Plant tomentulose ; column half as long as the anthers. 



4. A. arenaria. 

 Leaves ovate or lanceolate, or rarely oval, acute. 



Leaves ovate or ovate-lanceolate, more or less tomentose at least when 

 young ; hoods ovate-oblong to lanceolate, much exceeding the stamens. 



5. A. Hallii. 

 Leaves linear-lanceolate ; hoods truncate, little if any longer than the 



anthers. 

 Column short ; leaves pale, tomentose or puberulent when young. 

 Hoods about half as long as the anthers ; umbels peduncled. 



6. A. brachystephana 

 Hoods only slightly shorter than the anthers ; umbels subsessile. 



7. A. uncinalis. 

 Column more than half as long as the anthers ; corolla purple ; leaves 



glabrous. 8. A. incarnata. 



