184 American Midland Naturalist Monograph No. 7 



cymose, terminal, many-flowered ; leaves lanceolate, acute, 

 alternate, or a few opposite; follicles tomentulose, 7-15 cm 

 long, 1-1.5 cm thick; roadsides or open woods, common. 



June-Aug. Butterfly-weed [A. decumbens L.] A. tuberosa L. 



2. Flowers not orange or yellowy plants not hirsute; sap milky. 



3. Leaves narrowly linear, mostly in whorls of 4-6; flowers 



white; follicles erect, glabrous, narrowly lanceoloid, 6-10 



cm long, on erect pedicels; roadsides, or sandy soil in fields 



and open woods, common. June-Aug. Horsetail Milkweed 



- ...A. verticillata L. 



3. Leaves not narrowly linear. 



4. Leaves sessile or clasping, opposite (rarely some whorled) ; 

 plants glabrous, pale green, somewhat glaucous. 

 5. Follicles smooth; umbel solitary, terminal. 



6. Leaves elliptical, cordate-clasping, wavy-margined, 

 obtuse, mucronulate, 7-15 cm long; corolla pale 

 greenish-purple, 8-9 mm long; sandy soil along 

 roads and in open woods, extending southward to 



St. Clair and Wabash counties. June-July 



A. amplexicauUs Sm. 



6. Leaves lanceolate to ovate-lanceolate, sessile, flat, 

 acute or obtusish, 3-7 cm long, the margins minute- 

 ly roughened; flowers greenish-white; di*y ground, 

 rare; Fulton, Gallatin, Hancock, Henderson, and 



Peoria counties A. meadii Torr. 



5. Follicles somewhat echinate toward the apex with a few 

 short blunt processes, glabrous, 8-13 cm long, ovoid 

 or lanceoloid; umbels terminal and lateral; leaves 

 obtuse, mucronulate, elliptical, the margins flat; 

 prairie soil, or along roads, extending southward to 

 Coles, Bond, and Monroe counties. June-Aug. 



Smooth Milkweed A. sullivantii Engelm. 



4. Leaves manifestly petioled. 



7. Leaves pubescent beneath; fruiting pedicels deflexed. 



8. Follicles tomentose, 2-3 cm thick, warty with soft- 



spinulose subulate processes; flowers lavender and 



green; roadsides, fields, and woods, common 



throughout 111. June-Aug. Common Milkweed 



- -- A. syriaca L. 



8. Follicles smooth, less than 2 cm thick. 



9. Corolla-lobes dark purple, 8-10 mm long; hoods 

 red or purple; follicles 9-12 cm long; leaves 10- 

 20 cm long; sandy soil, along roads, and in open 



woods, local. June-July. Purple Milkweed 



A. purpurascens L. 



9. Corolla-lobes greenish-white tinged with purple, 

 4-5 mm long; hoods yellowish; tollicles 6-8 cm 

 long; leaves 5-8 cm long; open woods, rare; 



