Many honeysuckles are familiar garden plants. Except for the shrubby, weedy species, ours are more easily identified than the key might imply. An occasional exception to almost any character makes it necessary to evaluate several characters before naming some specimens.
The distinction based on pith in couplet 7 easily separates the weedy (and hybridizing) naturalized shrubs from a group of fine native species that have other good recognition characters that will, one by one, serve to identify them without resort to cutting a longitudinal section of twig to examine the pith; these characters can be reviewed in couplets 8–10 of the key.
Besides the more conspicuous bracts usually present at the summit of the peduncle of L. ×bella, L. canadensis, L. involucrata, L. maackii, L. morrowii, L. oblongifolia, L. tatarica, L. villosa, and L. xylosteum, there are useful characters often in the bracteoles (bractlets), usually very short and ± appressed to the ovaries. In L. villosa, however, the bracteoles form a cupule around the united ovaries, and in L. involucrata they are greatly enlarged though not quite as long as the bracts themselves, being part of the distinctive showy involucre.
1. Leaves (1–2 pairs) below inflorescences connate around the stem; flowers in clusters at the ends of branchlets (or at nodes with connate leaves); vine (twining or somewhat shrubby).
2. Corollas (2.8–) 3–5 cm long, the tube 1.7–4.2 cm; rare escape from cultivation.
3. Flowers sessile at bases of the connate leaves; corolla bilaterally symmetrical, 2-lipped, the lobes ± spreading; leaves glabrous.
3. Flowers in 1–3 whorls in a peduncled inflorescence; corolla nearly regular, the lobes ± equal and erect; leaves glabrous or at least slightly pubescent beneath.
2. Corollas (1.2–) 1.4–2.9 cm long, the tube (0.7–) 0.9–1.8 cm; native, in forests and thickets (except for L. reticulata).
4. Pair of connate leaves beneath inflorescence orbicular or nearly so, very glaucous above, broadly rounded or even shallowly notched at each leaf tip.
4. Pair of connate leaves beneath inflorescence distinctly longer than broad, not (or very little) glaucous above, ± acute at each leaf tip.
5. Leaves not ciliate, glabrous above; corolla tube (and branches of inflorescence) glabrous or with fine long straight hairs (overtopping any tiny glandular hairs).
5. Leaves with ± densely spreading-ciliate margins and at least sparsely strigose above; corolla tube (and usually branches of inflorescence) glandular-pubescent.
1. Leaves all distinct; flowers sessile (or ovaries even united) in pairs on axillary peduncles; plant an erect bushy shrub (slender vine only in L. japonica).
6. Plant a trailing or climbing vine; young stems and at least midrib of leaves above hairy; corolla ca. (2.5–) 3–5 cm long, the lobes nearly as long as the tube or longer; fruit purple-black, nearly sessile or on peduncles less than 10 (–15) mm long.
6. Plant an erect bushy shrub (at most, some of the branchlets slightly twisted); corolla less than 2.5 cm long; fruit and peduncles various.
7. Pith of twigs white and continuous; fruit red, blue, or deep purple-black; native, in forests or peatlands.
8. Peduncles, even in fruit, less than 1 cm long (rarely one to 1.5 cm); ovaries united (appearing as one, with 2 corollas), forming (in a cupule) a single blue-glaucous fruit per peduncle; corolla nearly regular, the lobes ± equal; bracts at base of ovary equaling or exceeding it at anthesis, but very narrow; pubescence of branchlets, petioles, lower leaf surface, and/or leaf margins mostly of straight ± brownish hairs or cilia.
8. Peduncles 1.1–3.5 (–4.5) cm long; ovaries separate or ± united, forming separate red or dark purple-black fruits or a 2-lobed one; corolla regular or 2-lipped; bracts at base of ovary broadly foliaceous or shorter than the ovary; pubescence, if any, less extensive (straight brownish hairs in L. canadensis, but limited to cilia on leaves).
9. Bracts apparently 4 at summit of peduncle, all foliaceous, covering ovaries and (until reflexing as a ruddy involucre) the 2 distinct purple-black berries; corolla nearly regular, the lobes ± equal and erect; leaves large (longest 9–13 cm or more), the apex short-acuminate or acute.
9. Bracts 2 at summit of peduncle (not including minute bracteoles), shorter than the ovaries (rarely one longer) and than the red to purplish berries united at their bases; corolla various; leaves shorter (very rarely over 9 cm long in L. canadensis), the apex rounded to obtuse or acute (not at all acuminate).
10. Leaf blades glabrous beneath or rarely with scattered long hairs (like the cilia); leaf margin and petiole ciliate; the 2 ovaries in a pair barely united at the base and strongly diverging (± 180°) in fruit; corolla nearly regular.
10. Leaf blades downy-puberulent beneath; leaf margin and petiole not ciliate; the 2 ovaries in a pair partly to fully united but both ascending (not divergent); corolla 2-lipped (lower lobes spreading).
7. Pith of twigs brown and hollow between the nodes; fruit orange to red; introduced, escaping to fields, borders of forests, etc.
11. Peduncles distinctly shorter than the subtending petioles (flowers and fruits sessile or subsessile); leaves acuminate.
11. Peduncles much longer than the subtending petioles; leaves merely acute or obtuse.
12. Leaves and young stems completely glabrous or with a very few hairs.
12. Leaves and at least young stems pubescent.
13. Ovary glandular; bracteoles glandular and pubescent on back and margins; filaments sometimes pubescent on distal half; leaf blades mostly broadest beyond the middle.
13. Ovary and bracteoles glandless; filaments glabrous except on basal half (or less); leaf blades broadest at or below the middle.
14. Bracteoles half or less as long as the ovary at anthesis.
14. Bracteoles more than half as long as the ovary at anthesis.