Lonicera is a moderately large genus of ca. 200 species, mostly native to the northern hemisphere. Two are native in Belgium as well, Lonicera periclymenum L. and L. xylosteum L.
About half of the species of the genus are cultivated for ornament. Their fruits (berries) are much eaten by birds and therefore easily dispersed. In addition to the taxa treated in detail in this account several others possibly also occur as escapes from cultivation. Clement & Foster (1994) cite several additional species. A cultivar of native Lonicera periclymenum with corollas that are pinkish-purplish outside is increasingly found in the wild, for instance in coastal scrub in Koksijde since several years (pers. obs.). In 2011 it was also observed near Verviers (see: http://waarnemingen.be/waarneming/view/55955784). Such plants possibly belong with cv 'Belgica'.
Lonicera xylosteum is a rare and local native species. It is naturally confined to calcareous soils, especially in the area between rivers Meuse and Sambre in Wallonia. However, outside its native distribution range it is increasingly found as an escape from cultivation in many, widely scattered locations, primarily in Flanders (disused railway yards, seadunes, abandoned cemeteries,…) (see also Duvigneaud 1988).
1. Climber, stems twining === 2
1. Erect or prostrate shrub === 7
2. Flowers in pairs === Lonicera japonica
2. Flowers in whorls === 3
3. Upper pair of leaves free, not united into a disc === 4
3. Upper pair of leaves fused === 5
4. Leaves lanceolate, acuminate at apex and slightly cordate at base, deciduous to semi-evergreen. Berry black. Inflorescence short-stalked (stalk at most 15 mm long). Young shoots hirsute-hairy === L. acuminata
4. Leaves oblong, more or less rounded at apex and tapered to base, deciduous. Berry bright red. Inflorescence long-stalked (stalk 25-45 mm long). Young shoots glabrous or minutely pubescent (native) === L. periclymenum
5. Evergreen. Corolla red with five equal, short lobes, glabrous outside === L. sempervirens
5. Deciduous. Corolla distinctly 2-lipped, cream or yellowish, sometimes tinged purplish, often glandular pubescent outside === 6
6. Bracteoles minute or absent === L. caprifolium
6. Bracteoles ca. ½ as long as ovary, obscuring its base === L. xitalica
7. Evergreen small shrub, rarely exceeding 100 cm (sometimes taller in cultivation). Corolla greenish yellow, minute (5-8 mm). Leaves glabrous, at most 30 mm long. Fruit violet === 8
7. Deciduous (or rarely semi-evergreen) shrub, usually much taller. Corolla cream, yellow or reddish, more than 8 mm long. Leaves larger, usually hairy (at least on the veins beneath when young). Fruit red or black === 9
8. Most leaves almost at right angles to the stem (90°), ca. 12-14 mm long. Leaf apex more or less rounded (leaves pointed egg-shaped). Adaxial leaf surface with median vein usually indistinct === L. nitida
8. Most leaves angled forwards at ca. 45°, ca. 20-26 mm long. Leaf apex attenuate (leaves narrowly elliptic). Adaxial leaf surface with median vein often raised, distinct === L. pileata
9. Each flower pair subtended by two very distinct, ovate bracteoles, these purple and enlarging in fruit. Berry black === L. involucrata
9. Bracteoles subulate or linear-lanceolate, indistinct (never purple and enlarging in fruit). Berry red === 10
10. Stem solid. Flowers appearing before leaves === L. xpurpusii
10. Stem hollow. Leaves appearing before flowers === 11
11. Corolla reddish or whitish, (10-) 15-30 mm long. Leaves and twigs almost glabrous === L. tatarica
11. Corolla cream, 8-25 mm long. Leaves and twigs densely and softly pubescent === 12
12. Inflorescence very shortly stalked, almost sessile, always shorter than leaf stalks === L. maackii
12. Inflorescence distinctly stalked, stalk always longer than leaf stalk === 13
13. Upper corolla lip split to base in 5 equal lobes. Ovary usually glabrous. Leaves and twigs more or less persistently hairy === L. morrowii
13. Upper corolla lip divided for at most ½ its length. Ovary glandular. Leaves and twigs eventually often more or less glabrescent === 14
14. Leaves 60-120 mm long, acuminate at apex. Upper corolla lip divided for ca. ½ its length. Corolla 15-20 (-25) mm long === L. chrysantha
14. Leaves 30-60 mm long, more or less acute at apex. Upper corolla lip divided for at most ¼ of its length. Corolla 8-12 mm long (native) === L. xylosteum
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