Herbs, with opposite simple entire leaves and regular flowers; sepals, petals, and stamens each 5; petals united; stamens attached to the corolla; ovaries 2, with a single style or stigma. 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. 8a. Reflexed lobes of corolla merely purple-tinged (1-2 m. high) =Milkweed, Asclepias syriaca.= 8b. Reflexed lobes of corolla bright-red or purple --9. 9a. The erect hoods of each flower about 5 mm. long (7-12 dm. high) =Milkweed, Asclepias purpurascens.=