Caprifoliaceae, the Honeysuckle Family
Shrubs or herbs, with opposite leaves; corolla regular or irregular, petals 4 or 5, united; stamens 4 or 5; ovary inferior, 1-5-celled.
| 1a. Leaves compound (shrubs 1-4 m. high; flowers white, in large clusters in early summer) (Elder) — 2. | |
| 1b. Leaves simple — 3. | |
| 2a. Pith of the twigs white; inflorescence flattened or convex | Elder, Sambucus canadensis. |
| 2b. Pith of the twigs brown; inflorescence pyramidal | Elder, Sambucus racemosa. |
| 3a. Plant trailing; flowers nodding, in pairs (1 dm. high; flowers pink, summer) | Twin Flower, Linnaea borealis var. americana. |
| 3b. Erect herbs (6-12 dm. high; flowers dull-red, axillary, early summer) (Feverwort) — 4. | |
| 3c. Shrubs, small trees, or woody vines — 5. | |
| 4a. Leaf-bases broadly connate and 2-5 cm. wide | Feverwort, Triosteum perfoliatum. |
| 4b. Leaf-bases narrowly connate, not over 1 cm. wide | Feverwort, Triosteum aurantiacum. |
| 5a. Climbing vines (spring and early summer) (Honeysuckle) — 6. | |
| 5b. Erect or spreading shrubs or small trees — 11. | |
| 6a. Flowers in 2-flowered axillary clusters (flowers white or pink) | Honeysuckle, Lonicera japonica. |
| 6b. Flowers in terminal clusters — 7. | |
| 7a. Leaves distinctly pubescent beneath (flowers yellow) — 8. | |
| 7b. Leaves glabrous beneath, or very minutely puberulent — 9. | |
| 8a. Leaves pubescent above | Honeysuckle, Lonicera hirsuta. |
| 8b. Leaves glabrous above | Honeysuckle, Lonicera glaucescens. |
| 9a. Corolla purple on the outside, glabrous within | Honeysuckle, Lonicera caprifolium. |
| 9b. Corolla yellow on the outside (or slightly tinged with purple), pubescent within — 10. | |
| 10a. Corolla-tube 6-8 mm. long | Honeysuckle, Lonicera dioica. |
| 10b. Corolla-tube 11-14 mm. long | Honeysuckle, Lonicera sullivantii. |
| 11a. Corolla tubular at base; style long and slender — 12. | |
| 11b. Corolla rotate or somewhat bell-shape, style very short (flowers white, late spring or early summer) — 22. | |
| 12a. Flowers yellow or yellowish (spring and early summer) — 13. | |
| 12b. Flowers white, pink, or red — 18. | |
| 13a. Leaves serrate (5-10 dm. tall) | Bush Honeysuckle, Diervilla lonicera. |
| 13b. Leaves entire; flowers in pairs (Honeysuckle) — 14. | |
| 14a. Each pair of flowers subtended by 2 broad leaf-like bracts (1-3 m. high) | Honeysuckle, Lonicera involucrata. |
| 14b. Bracts at the base of each pair of flowers linear or narrowly lanceolate — 15. | |
| 15a. Native species of woods and bogs — 16. | |
| 15b. Introduced species, growing mostly near dwellings; leaves very pubescent beneath | Honeysuckle, Lonicera xylosteum. |
| 16a. Peduncles 15 mm. long or more (1-4 m. high) — 17. | |
| 16b. Peduncles about 5 mm. long (1 m. high, or less) | Honeysuckle, Lonicera coerulea var. villosa. |
| 17a. Leaves ciliate | Honeysuckle, Lonicera canadensis. |
| 17b. Leaves not ciliate | Honeysuckle, Lonicera oblongifolia. |
| 18a. Corolla irregular, over 1 cm. long (1-4 m. high; spring) | Honeysuckle, Lonicera tatarica. |
| 18b. Corolla regular, less than 1 cm. long (5-15 dm. high; flowers white or pink, in axillary clusters, early summer) — 19. | |
| 19a. Flowers in axillary spikes | Wolfberry, Symphoricarpos occidentalis. |
| 19b. Flowers almost sessile in the axils — 20. | |
| 20a. Flowers numerous in each axil | Indian Currant, Symphoricarpos orbiculatus. |
| 20b. Flowers 1 or 2 in each axil (Snowberry) — 21. | |
| 21a. Leaves green beneath | Snowberry, Symphoricarpos racemosus. |
| 21b. Leaves whitened beneath | Snowberry, Symphoricarpos racemosus var. pauciflorus. |
| 22a. Leaves palmately lobed — 23. | |
| 22b. Leaves not lobed — 25. | |
| 23a. Outermost flowers of the cluster enlarged and imperfect (1-4 m. high) | Cranberry Tree, Viburnum opulus var. americanum. |
| 23b. All flowers of the cluster alike — 24. | |
| 24a. Flower-clusters 4-10 cm. broad (1-2 m. high) | Arrow Wood, Viburnum acerifolium. |
| 24b. Flower-clusters 2-3 cm. broad | Squashberry, Viburnum pauciflorum. |
| 25a. Outer flowers of the cluster enlarged and imperfect (1-3 m. high) | Hobble-bush, Viburnum alnifolium. |
| 25b. All flowers of the cluster alike — 26. | |
| 26a. Leaves finely serrate; the veins not prominent — 27. | |
| 26b. Leaves coarsely serrate, all or most of the teeth terminating in a prominent vein — 29. | |
| 27a. Peduncle of the flower-cluster, below its branches, at least 2 cm. long (1-3 m. high) | Withe-rod, Viburnum cassinoides. |
| 27b. Peduncle of the cluster 1 cm. long, or even shorter (3-8 m. high) — 28. | |
| 28a. Leaves distinctly acuminate | Sheep-berry, Viburnum lentago. |
| 28b. Leaves obtuse or barely acute | Black Haw, Viburnum prunifolium. |
| 29a. Leaves densely pubescent beneath (6-15 dm. high) | Arrow-wood, Viburnum pubescens. |
| 29b. Leaves glabrous beneath, or with tufts of hairs in the forks of the veins (1-4 m. high) | Arrow-wood, Viburnum dentatum. |