Polygalaceae, the Milkwort Family
Small herbs, with alternate or whorled simple leaves, and small irregular flowers; sepals 5, petals 3, stamens 6 or 8, more or less united with each other and with the petals.
| 1a. All of the leaves alternate — 2. | |
| 1b. Some or all of the leaves in whorls (1-4 dm. high; flowers greenish, purple, or white; summer) (Milkwort) — 6. | |
| 2a. Flowers few, loosely clustered, 15-20 mm. long (1-3 dm. high; flowers purple; early summer) | Flowering Wintergreen, Polygala paucifolia. |
| 2b. Flowers numerous, in a spike or raceme — 3. | |
| 3a. Stem-leaves minute, linear-subulate; stem slender, erect, 3-7 dm. high (flowers pink; summer) | Milkwort, Polygala incarnata. |
| 3b. Stem-leaves narrowly oblong or broader; stem generally 1-4 dm. high — 4. | |
| 4a. Flowers in a short thick obtuse very dense spike (flowers greenish or purple; summer) | Milkwort, Polygala sanguinea. |
| 4b. Flowers in a slender tapering spike — 5. | |
| 4c. Flowers in a raceme; plants with subterranean flowers also (flowers purple; early summer) | Milkwort, Polygala polygama. |
| 5a. Leaves linear or nearly so (flowers purple; summer) — 7b. | |
| 5b. Leaves lanceolate or oblong-lanceolate, 2-6 cm. long (flowers white; late spring) | Seneca Snakeroot, Polygala senega. |
| 5c. Leaves ovate to ovate-lanceolate (flowers white; late spring) | Seneca Snakeroot, Polygala senega var. latifolia. |
| 6a. Spike oval, thick, obtuse | Milkwort, Polygala cruciata. |
| 6b. Spike acute — 7. | |
| 7a. Spike densely flowered, 1-2 cm. long | Milkwort, Polygala verticillata. |
| 7b. Spike loosely flowered, 2-5 cm. long | Milkwort, Polygala verticillata var. ambigua. |