Primulaceae, the Primrose Family
Herbs, with alternate or opposite simple leaves and regular flowers; petals more or less united; stamens attached one in front of each petal; ovary 1-celled with 1 style.
| 1a. Leaves all basal; flowers on leafless stalks — 2. | |
| 1b. Stem-leaves present — 5. | |
| 2a. Flowers nodding, the petals reflexed (3-6 dm. high; flowers showy, white or pink, in spring) | Shooting Star, Dodecatheon meadia. |
| 2b. Flowers erect or spreading; petals not reflexed — 3. | |
| 3a. Corolla not longer than the calyx; flowers small and inconspicuous (1 dm. high; flowers white or pink, spring) | Androsace, Androsace occidentalis. |
| 3b. Corolla conspicuous, much longer than the calyx (flowers pink or purple, summer) (Primrose) — 4. | |
| 4a. Leaves white-mealy beneath (1-4 dm. high) | Primrose, Primula farinosa. |
| 4b. Leaves green beneath (2 dm. high or less) | Primrose, Primula mistassinica. |
| 5a. All the stem-leaves in one whorl just below the flower-cluster — 6. | |
| 5b. Stem-leaves several or many, scattered over the stem — 7. | |
| 6a. Stem-leaves about 1 cm. long — 3a. | |
| 6b. Stem-leaves 5-10 cm. long | Star Flower, Trientalis americana. |
| 7a. Flowers red, blue, or white (summer) — 8. | |
| 7b. Flowers yellow (summer) — 9. | |
| 8a. Leaves opposite; flowers axillary (stems spreading, 1-4 dm. long; flowers blue or red) | Pimpernel, Anagallis arvensis. |
| 8b. Leaves alternate; flowers racemose (1-4 dm. high; flowers minute, white) | Water Pimpernel, Samolus floribundus. |
| 9a. Stem creeping | Moneywort, Lysimachia nummularia. |
| 9b. Stem erect (Loosestrife) — 10. | |
| 10a. Flowers in dense spike-like racemes (3-8 dm. high) | Loosestrife, Lysimachia thyrsiflora. |
| 10b. Flowers axillary or racemose (3-9 dm. high) — 11. | |
| 11a. Corolla dotted or streaked with purple or brown; leaves punctate with dark spots — 12. | |
| 11b. Corolla plain yellow; leaves not dark-dotted — 14. | |
| 12a. Flowers in racemes — 13. | |
| 12b. Flowers all axillary | Loosestrife, Lysimachia quadrifolia. |
| 13a. Flowers all in racemes; leaves opposite or some of them alternate | Loosestrife, Lysimachia terrestris. |
| 13b. The lowest flowers axillary; leaves opposite or whorled | Loosestrife, Lysimachia producta. |
| 14a. Leaves ovate, on slender ciliate petioles | Loosestrife, Steironema ciliatum. |
| 14b. Leaves lanceolate, sessile or short-petioled, pinnately veined | Loosestrife, Steironema lanceolatum. |
| 14c. Leaves linear, with one mid-vein | Loosestrife, Steironema quadriflorum. |