CAPRIFOLIACEAE: Honeysuckle family
KEY TO LONICERA SPECIES
1. Twigs with vegetative parts only .............................................. 2
2. Internodes of year 2 twigs with continuous pith or rarely partly excavated ............................................................................ 3
3. Petiole of largest leaves with stiffish spreading hairs .. L. standishii
3. Petiole glabrous or with scattered soft spreading hairs ................. 4
4. Midvein of leaf blade indistinctly reaching apex ...... L. canadensis
4. Midvein of leaf blade prominently protruding ...... L. fragrantissima
2. Internodes of year 2 twigs hollow, pith absent ............................. 5
5. Some of upper pair of leaves with blades fused at bases. Flowers usually in whorls of 6 at end of twigs ............................................. 6
6. Underside of leaf blade prominently glaucous .............. L. dioica
6. Underside of leaf blade light green to pale ................ L. flava
5. Leaf blades all separate. Flowers in pairs on axillary peduncles (occasionally some in terminal panicles in No. 6) ....................... 7
7. Year 1 twigs glabrous, scattered hairs rare ............. L. tatarica
7. Year 1 twigs distinctly hairy ........................................ 8
8. Leaf blade apex acuminate .. ...................... L. maackii
8. Leaf blade apex acute to obtuse or rounded ....................... 9
9. Buds obtusish, nearly glabrous. Apex of most leaf blades mucronate. Petiole mostly 2-3 mm ................. L. morrowii
9. Buds pointed, scales hairy and ciliate. Apex of leaf blades not mucronate.
..... L. japonica
1. Twigs with leaves and flowers ................................................ 10
10. Corolla 30-50 mm ............................................. L. japonica
10. Corolla 5-25 mm .......................................................... 11
11. Flowers in terminal clusters .......................................... 12
12. Corolla straw-colored to greenish-yellow, brick red, or purplish, 15-25 mm, base bulging on one side near base ................... L. dioica
12. Corolla bright orange-yellow, 20-37 mm, base not bulging on one side, sometimes bulging a few mm above base ..................... L. flava
11. Flowers in axillary clusters .......................................... 13
13. Flowers united by hypanthium in pairs .............................. 14
14. Peduncle over 12 mm ................................ L. tatarica
14. Peduncle under 12 mm ........................................... 15
15. Peduncle and outerside of corolla glabrous ............................................ L. fragrantissima
15. Peduncle and outerside of corolla with stiff hairs ................................................ L. standishii
13. Flowers all separate ............................................... 16
16. Peduncle shorter than adjacent petiole .............. L. maackii
16. Peduncle much longer than adjacent petiole ............ ... 17
17. Corolla nearly regular, tube 8-13 mm .......... L. canadensis
17. Corolla 2-lipped, tube 3-7.3 mm ............................. L. morrowii