Apocynaceae, the Dogbane Family
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. |