igma.

1a. Plant creeping or trailing; flowers blue, axillary, 2-3 cm. broad
(spring) =Periwinkle, Vinca minor.=

1b. Plant erect or essentially so; flowers 1 cm. broad or less (4-12 dm.
high) --2.

2a. Corolla pinkish, about 8 mm. long by 6-8 mm. broad (early
summer) =Dogbane, Apocynum androsaemifolium.=

2b. Corolla white or greenish, about 6 mm. long by 4 mm. broad
(summer) --3.

3a. Leaves petioled, acute at the base
=Indian Hemp, Apocynum cannabinum.=

3b. Leaves sessile, rounded or truncate at the base
=Indian Hemp, Apocynum cannabinum var. hypericifolium.=

ASCLEPIADACEAE, the Milkweed Family

Herbs, with simple entire leaves and regular flowers; juice usually
milky; except in the first species, which is a twining vine. The flowers
have an unusual structure: calyx of 5 sepals; petals 5, united with each
other, and spreading or reflexed so that they conceal the calyx; stamens
5, united with each other and with the stigma to form a complex organ in
the center of the flower; ovaries 2; on the back of each stamen is a
colored projecting hood, which is frequently the most conspicuous part
of the flower, and may be mistaken for the corolla.

1a. Twining vine, with dark purple flowers (summer)
=Black Swallow-wort, Cynanchum nigrum.=

1b. Stems not twining --2.

2a. Leaves whorled (3-6 dm. high; summer) (Milkweed) --3.

2b. Leaves opposite or alternate --4.

3a. Leaves in whorls of 4, lanceolate (flowers pink)
=Milkweed, Asclepias quadrifolia.=

3b. Leaves in whorls of 4-7, linear (flowers greenish-white)
=Milkweed, Asclepias verticillata.=

4a. Umbel sessile (4-8 dm. high; flowers green, summer)
=Green Milkweed, Acerates viridiflora.=

4b. Umbel peduncled --5.

5a. Leaves linear or narrowly linear-lanceolate (4-8 dm. high; flowers
greenish-white, summer) =Green Milkweed, Acerates floridana.=

5b. Leaves lanceolate or broader (flowers in summer) --6.

6a. Leaves pubescent beneath --7.

6b. Leaves glabrous or nearly so --10.

7a. Flowers brilliant orange (3-6 dm. high)
=Butterfly Weed, Asclepias tuberosa.=

7b. Flowers red or purple --8.