MILKWEED FAMILY 671 



1. A. lanuginosa (Nutt.) DC. Stem erect, 1^ dm. high; leaves oblong or 

 elliptic, short-petioled, 3-10 cm. long; corolla greenish; lobes oblong, about 5 

 mm. long; hood purplish, oblong, with an auricle or fold on the ventral margins. 

 Prairies: 111. — Alinn. — Mont. — Wyo. Je-Au. 



2. A. viridiflora (Raf.) Eat. Stem 2-6 dm. high, often decumbent; leaves 

 oval or oblong and obtuse or retuse or acute, or elongated lanceolate and acumin- 

 ate (var. Ivesii Britton), or narrowly Unear (var. linearis A. Gray), becoming 

 leathery, with undulate margins; um.bels sessile or nearly so, many-flowered; 

 corolla-lobes oblong-lanceolate, about 5 mm. long; hood dull purple or at least 

 tinged with purple, lance-oblong, entire except for the small infolded auricles at 

 the base. Dry or sandy soil: Mass. — -Fla. — N.M. — Mont. Plain — Submont. 

 Jt^Jl. 



3. A. auriculata Engelm. Stem 2-8 dm. high, mostly soHtary; leaves 

 alternate, scattered, narrowly hnear, 5-15 cm. long, with scabrous, often revolute 

 margins; coroUa-lobes gi'eenish, about 4 mm. long; hood yellowish, with purplish 

 keel, erect, emarginate or truncate, the involute sides with broad auricles at the 

 base. Plains and prairies: Neb. — Utah — X.M. — Tex. Plain — Submont. Je- 

 Au. 



4. A. angustifolia (Xutt.) Dec. Stem several from a thick rootstock, 3-6 

 dm. high, puberulent or glabrate in age; leaves narrowly linear, 5-12 cm. long, 

 revolute-margined ; umbels subsessile ; corolla-lobes 5 mm. long, oblong, greenish; 

 hood white, erect, as high as the anthers, laterally compressed, 3-dentate at the 

 apex, the inner margins •^'ith an erose truncate lobe. Asclepias stenophylla A. 

 Gray. Dry plains: S.D. — Colo. — Tex. — Mo. Plain. Je-Au. 



4. ASCLEPIAS (Tourn.) L. Milkweed, Silkweed, Butterfly-weed. 



Perennial herbs, with deep taproots, sometimes woody at the base. Leaves 

 opposite, alternate, or whorled. Flowers perfect, regular, in axillarj' or terminal 

 umbels. Calyx small, usually with smaU glands at the base of the 5 lobes. 

 Corolla rotate, deepl}^ 5-cleft; lobes valvate-convolute in bud, reflexed in anthesis. 

 Hoods of the crown involute, arising from the base of the corolla-lobes or on a 

 short column, concave, hooded, bearing within a horn- or tooth-like projection, 

 and sometimes additional processes between the anthers. Folhcles fusiform, 

 naked or wth soft processes or warty. Seeds mostly with a coma. 



Plant more or less hirsute; hoods orange; leaves mostly alternate; juice not milkj'. 



1. A. tuberosa. 

 Plant not hirsute; hoods greenish, purplish, yellowish, or white; leaves mostly opposite 



or verticillate; juice milky. 

 Leaves orbicular to linear-lanceolate, opposite fexcept No. 14'). 



FolUcles with soft spinulose processes, tomentose; leaves large and broad, tomen- 

 tose, transversely veined, oval or ovate. 

 Hoods oblong-ovate, obtuse, sUghtly exceeding the stamens. 



2. A. syriaca. 

 Hoods lanceolate, produced, about three times as long as the stamens. 



3. A. speciosa. 

 Follicles without process&s. 



Flowers very large; petals over 1 cm. long; column none; corolla spherical in 

 outline ; horns included in the hoods ; leaves almost orbicular, sub-cordate 

 at the base. 4. A. cryptoceras. 



Flowers middle-sized or small ; petals much less than 1 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 yoimg, glabrate in age; column very short. 



5. A. lalifolia. 

 Plant tomentulose ; column half as long as the anthers. 



6. A. arenaria. 

 Leaves ovate or lanceolate, or rarely oval, acute. 



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

 yoimg. 

 Hoods truncate, sUghtly longer than the anthers; leaves sessile, 



with rounded or subcordate bases. 7. A. erosa. 



Hoods ovate-oblong to lanceolate, much exceeding the stamens; 

 leaves petioled. 

 Corolla yellowish; hoods with a tooth on each margin, not 

 auricled or gibbous at the base ; peduncles shorter than the 

 pedicels. 8. A. ovalifolia. 



