The biology of Canadian weeds. 135. Lonicera japonica Thunb. Brendon M. H. Larson1, Paul M. Catling2, and Gerald E. Waldron3 1Department of Environment and Resource Studies, University of Waterloo, Waterloo, Ontario, Canada N2L3G1; 2Biodiversity, National Program on Environmental Health, Agriculture and Agri-Food Canada, Research Branch, Saunders Bldg., Central Experimental Farm, Ottawa, Ontario, Canada K1A 0C6; 37641 County Road 20, R. R. #1, Amherstburg, Ontario, Canada N9V 2Y7. Received 18 April 2006, accepted 14 December 2006. Larson, B. M. H., Catling, P. M. and Waldron, G. E. 2007. The biology of Canadian weeds. 135. Lonicera japonica Thunb. Can. J. Plant Sci. 87: 423–438. Japanese honeysuckle (Lonicera japonica Thunb.) is a twining semi-evergreen vine native to Japan, Korea and eastern China. Over the past 150 yr it has been introduced as an ornamental and become established in temperate and tropical regions worldwide. It was first discovered in Canada in 1976 in southwestern Ontario woodlands and has since been found growing without cultivation in 15 localities. While L. japonica does not occur very frequently in southern Ontario, climate change models suggest that it may become more abundant in this region. Its predominance elsewhere derives from morphological and physiological characteristics that allow it to be particularly successful in the edge habitats of fragmented landscapes. Through extensive vegetative propagation and competitive ability it occupies space which may otherwise host a diverse native flora. The plant has many uses in Asian medicine and is a popular ornamental, but has been prohibited in some regions due to its displace- ment of other species. A combination of cutting and foliar application of glyphosate has proven to be an effective control method in some circumstances. Planting of L. japonica should be discouraged and horticulturalists should consider alternative attractive vines. The spread of L. japonica should be monitored in Ontario and control of newly established populations should be consid- ered to avoid costly large scale control in the future. Key words: Invasive species, Lonicera japonica, weed biology, climate change Larson, B. M. H., Catling, P. M. et Waldron, G. E. 2007. La biologie des mauvaises herbes au Canada. 135. Lonicera japon- ica Thunb. Can. J. Plant Sci. 87: 423–438. Le chèvrefeuille du Japon (Lonicera japonica Thunb.) est une vigne volubile mi-sem- pervirente originaire du Japon, de la Corée et de l’est de la Chine. Introduite il y a 150 ans comme plante ornementale, elle s’est implantée dans toutes les régions tempérées et tropicales de la planète. L’espèce a été découverte pour la première fois au Canada en 1976, dans des boisés du sud-ouest de l’Ontario. Depuis, on la retrouvée à 15 endroits sans qu’elle y ait été plantée. Bien que L. japonica ne se rencontre pas souvent dans le sud de l’Ontario, les modèles du changement climatique laissent croire qu’elle pourrait devenir plus abondante dans cette région. Ailleurs, on doit sa prédominance à ses caractéristiques morphologiques et phys- iologiques qui lui permettent de prospérer dans les habitats à la lisière des reliefs morcelés. Une forte multiplication végétative et une bonne compétitivité lui permettent d’occuper les espaces où se développerait normalement une flore indigène plus diversifiée. Cette plante a maints usages dans la pharmacopée asiatique et est populaire en horticulture, mais on en a interdit la culture dans certaines régions à cause de sa propension à supplanter d’autres espèces. La coupe combinée à l’application de glyphosate s’avère efficace comme méthode de lutte dans certaines circonstances. On déconseille aux horticulteurs de planter L. japonica en leur sug- gérant d’opter pour d’autres vignes aussi attrayantes. Il conviendrait de surveiller la propagation de L. japonica en Ontario et de détruire les nouveaux peuplements si l’on veut s’épargner une lutte plus ardue et plus coûteuse dans l’avenir. Mots clés: Espèce envahissante, Lonicera japonica, biologie des mauvaises herbes, changement climatique 1. Names - Aug.). Common synonyms include Nintooa japonica Lonicera japonica Thunb. – Japanese honeysuckle (Catling (Thun.) Sweet and Caprifolia japonicum (Thunb.) Kuntze. 1997; Nuzzo 1997), Chinese honeysuckle (often referring to The variety halliana (Dippel) G. Nicholson is a well-known var. chinensis), Hall’s honeysuckle (often referring to var. cultivated variety that has escaped in northeastern North halliana), woodbine (in older textbooks, Nuzzo 1997). America. This and other varieties, including chinensis (P. Chèvrefeuille du Japon (Erhaeghe 2004), clématite du Japon Watson) Baker, repens (Hort Bogor. ex Seibold) Rehder, (USDA 2005), ren dong (Chinese, USDA 2005), nindo and aureo-reticulata (T. Moore) Jacob-McKoy) are treated (Japanese, USDA 2005), suikazura (Japanese, USDA 2005), as synonyms by most authors. madreselva (Spanish, USDA 2005), Caprifoliaceae, honey- The genus name Lonicera commemorates German natu- suckle family, Caprifoliacées. ralist Adam Lonitzer (1528–1586). The specific epithet Lonicera japonica Thunb. ex Murray (Systemat japonica refers to Japan, where it is native. The horticultur- Vegetabilium, ed. 14: 216. 1784 - May–June) has priority al variety name halliana refers to Dr. George Hall, who over Lonicera japonica Thunb. (Flora Japonica 89–90. 1784 introduced it to the United States in 1862 (Coombes 1991). 423 424 CANADIAN JOURNAL OF PLANT SCIENCE Lonicera japonica is placed in subgenus Chamaecerasus cascade”, “mint crist”, “Interold Darts World” (the latter on the basis of twining growth and flowers in axillary pairs with purple-crimson flowers), are widely available. (Sax and Kribs 1930). Schierenbeck et al. (1995) compared allozyme variability of L. japonica with sympatric L. sempervirens L. in the 2. Description and Account of Variation southeastern United States. Among 10 populations in South (a) Description – Perennial, semi-evergreen (in Canada) Carolina and Georgia, L. japonica had 75% polymorphic twining and trailing vine (Fig. 1), ascending to 10 m, but in loci (Ps), 1.96 alleles per locus (As), 2.28 alleles per poly- Canada rarely more than 4 m high. Younger stems reddish- morphic locus (Aps), and a total genetic diversity (Ht) of brown or light brown and pubescent, becoming woody, hol- 0.216. This variation was consistently lower than L. sem- low, brownish and glabrous with age, and eventually pervirens, but genetic variation within both species was developing a bark that peels off in long strips. Leaves oppo- equivalent to that of other species with similar life history site, ovate or oblong, acute or obtuse and apiculate, entire or characters. early leaves more or less lobed, pubescent but becoming More recently, Peng et al. (2005) found differing concen- glabrous above, relatively thick, 3–8 cm long and 1–3.5 cm trations of two polyphenolic compounds (hyperoside and wide, with pubescent petioles 0.4–1 cm long. Flowers white, chlorogenic acid) among samples of L. japonica from three sometimes with some external purple (or red in var. chinen- Chinese populations, whereas the concentrations of two oth- sis), becoming yellowish on the second day after opening, ers (luteolin and caffeic acid) were similar among popula- 3–4 cm long, glandular-pubescent externally, with a slender tions. tube and with two spreading and recurved lips at the apex, fragrant, produced all summer in axillary pairs on branches 3. Economic Importance 5–15 mm long on young shoots, often crowded at the shoot (a) Detrimental – Lonicera japonica is considered a prob- tips, with calyx glandular-pubescent or smooth, 1–2 mm lematic invader around the world because it displaces native long, the individual flowers sessile and attached at the sum- species and competes with cultivated plants. For example, it mit of a pedicillate ovary 2–3 mm long, subtended by a pair is considered a serious threat to the flora of the Juan of ovate bracts 1–2 cm long. Stamens 5, attached to and Fernandez Islands, Chile (Swenson et al. 1997) and to native about as long as the corolla. Style about as long as the corol- vegetation in southern Australia (Carr et al. 1992), where it la. Ovary inferior, developing into a globose or oval, black occurs in diverse plant associations including heathlands, or purple-black, pulpy berry 6–7 mm long (Fig. 2), which sclerophyllous forest, riparian scrub and temperate rainfor- matures from September (in Ontario) to November (in est. In Hawaii it contributes to the decline of the endangered southeastern US). Seeds 1–16 (average 6) in each fruit, endemic naenaè, Dubautia latifolia (A. Gray) Keck (Starr et brown or brownish-black, ovate or oblong, flat, 2–3 mm al. 2003). In many parts of the world where it has estab- long, each ca. 3.6 mg. See Fig. 3 for illustration of a lished, further planting of L. japonica is discouraged and its seedling. Description from Bailey (1949), Fernald (1950), spread is monitored so that new populations can be rapidly Schierenbeck (2004) and examination of living and herbari- um specimens. controlled, thus avoiding more expensive control later. The normal chromosome number for L. japonica is 2n = More than 50 yr ago, Fernald (1950) described L. japoni- 18. Wang and Wang (2005) provide details on its karyotype. ca in the United States as “a most pernicious and dangerous weed, overwhelming and strangling the native flora and (b) Distinguishing features – Lonicera japonica is easily most difficult to eradicate … [it is] extensively planted and distinguished from other northeastern North American encouraged by those who do not value the rapidly destroyed Lonicera because it is a twining vine with separate leaves indigenous vegetation (Fernald 1950).” In Michigan, adja- and flowers in pairs on axillary peduncles (Fig. 1). Other cent to its area of occurrence in southwestern Ontario, it has Lonicera vines are either rare escapes (L. sempervirens L.) been considered “an aggressive vine that defies eradication, or infrequent natives (L. hirsuta Eat. and L. dioica L.) with forming dense tangles that overwhelm the native vegeta- leaves below the inflorescence encircling the stem and flow- tion” (Voss 1996).