Canadian Journal of Plant Science The Biology of Canadian Weeds. [#]. Daphne laureola L. Journal: Canadian Journal of Plant Science ManuscriptFor ID CJPS-2017-0247.R1 Review Only Manuscript Type: Article Date Submitted by the Author: 15-Feb-2018 Complete List of Authors: Strelau, Matthew; Trinity Western University, Biology Clements, David; Trinity Western University, Biology Webb, Conan; Parks Canada, Fort Rodd Hill National Historic Site of Canada Prasad, Raj; Natural Resources Canada, Pacific Forestry Centre Keywords: Daphne laureola L, Thymelaeaceae, toxicity, coumarins, mezerein https://mc.manuscriptcentral.com/cjps-pubs Page 1 of 35 Canadian Journal of Plant Science The Biology of Canadian Weeds. [#]. Daphne laureola L. M. Strelau1, D.R. Clements1, C. Webb2, and R. Prasad3 1Department of biology, Trinity Western University, Langley, BC V2Y 1Y1 (e-mail: [email protected]) 2Parks Canada, Fort Rodd Hill National Historic Site of Canada, Victoria, BC, V9C 2W8 3Natural Resources Canada,For Pacific Review Forestry Centre, 506Only Burnside Rd., Victoria, BC, V8Z 1M5 Strelau M., Clements D.R., Webb, C. and Prasad, R. 2017. The biology of Canadian weeds. #. Daphne laureola L. Can. J. Plant Sci. xx: xxx-xxx. Daphne (Daphne laureola L.) is a perennial evergreen shrub native to Eurasia and Northern Africa. Introduced to North America as an ornamental shrub, the plant has readily absconded gardens and can now be found throughout suitable habitats on both the east and west coasts of the continent. In Canada, daphne has naturalized in southwestern British Columbia including Vancouver, southern Vancouver Island, and the Gulf Islands. Daphne is of particular concern to the endangered Garry oak (Quercus garryana Douglas) because it invades shady woodland areas, forming dense mono-specific stands that can suppress and inhibit native vegetation. The berries and all other parts of the daphne plant contain a mixture of toxic chemicals that can be fatal to humans or animals if ingested. Removal teams suggest using gloves for elimination and handling of daphne because of its corrosive sap and oil. Widespread planting combined with a lack of public knowledge regarding the species’ invasiveness has created great concern over its potential to spread. Various methods of control (chemical, manual, and biological) have been developed. The most commonly applied approach in Canada is manual control, but care must be taken to avoid contact 1 https://mc.manuscriptcentral.com/cjps-pubs Canadian Journal of Plant Science Page 2 of 35 with skin and follow-up monitoring and control is advised. A promising biocontrol agent is the fungus Phomopsis sp. Nov., which has been observed to cause high levels of mortality in D. laureola under both laboratory and field conditions. Key Words: Daphne laureola L., Thymelaeaceae, toxicity, coumarins, mezerein 1. Names For Review Only Daphne laureola L.; daphne, spurge-laurel, daphne-laurel, laurel-leafed daphne, olive-spurge, dwarf bay, false-laurel, daphné lauréole, laurier des bois, laurier purgatif, laurier des anglais, laurier épurge, auréole, zwart peperboompje (GOERT 2007; USDA GRIN 2008) Thymelaeaceae, Mezereon family, Thyméléacées. Bayer Code: DAPLA. (GOERT 2007; NSF Center for Integrated Pest Management 2016). The Thymelaeaceae family encompasses more than 400 species including the Daphne L. genus which contains 95 species primarily located in Asia (Noshad 2007; Rogers 2009). Though no native species exist within Canada, Daphne × mantensiana Manten ex T.M.C. Taylor & Vrugtman is a cultivated hybrid in British Columbia (Tropicos.org undated). Variation within the species has led to taxonomic debate with several intraspecific divisions being recognized (Feliner 1996 and Castilla et al. 2012). 2. Description and Account of Variation (a) Species Description Daphne laureola is a perennial evergreen shrub 0.4 to 1.5 m tall (Figs. 1 and 2) (Alonso and Herrera 1996). See also photographs in the Electronic Atlas of the 2 https://mc.manuscriptcentral.com/cjps-pubs Page 3 of 35 Canadian Journal of Plant Science Flora in British Columbia (<http://linnet.geog.ubc.ca/Atlas/Atlas.aspx?sciname=Daphne%20laureola>). Stems are brown, flexible, erect, but often prostrate for a portion of their length. Stem branching can vary and lead to different architectural shapes (Alonso et al. 2004). Leaves are alternate oval to oblanceolate, tapering towards the base, 4-13 cm long and 1-3 cm wide, evergreen, dark green on top and light on the underside, glossy and clustered in distinct whorls at the distal end of branches (Alonso and Herrera 2003; Ramdani et al. 2015). Leaf size has been demonstrated to double in size from AprilFor to June (AlonsoReview and Herrera 2003).Only Flowers are formed in an almost sessile axillary raceme, tubular yellowish-green, and 6-12 mm long. These odourless, uninviting or slightly fragrant flowers are clustered close to the stem at tips of branches (Fig. 2a). The calyx forms a tubular structure with four spreading lobes; eight yellow stamens are inserted in 2 rows on the tube, the filaments are short; the ovary is one-celled, short or with almost no style, stigma is large, capitate (Fig. 1). Fruits ripen in early June and are black, fleshy, single-seeded ovoid drupes, 8-11 mm long (Fig. 1). Spurge laurel has been observed to grow up to 600 fruits per plant, on average 19.4 fruits per stem (Byrne and Robinson 2005; Castilla et al. 2011). The fruit is frequently disseminated by birds and mice, as well as toxic to most mammals, including humans (Barton 1989; Diogo 2009). Fig. 2A displays juvenile daphne seedlings. The sporophyte chromosome number from live D. laureola specimens has been reported to contain a single cytotype; a diploid chromosomal base number of 9 (2n=2X=18) (Goldblatt and Johnson 1981; Ivanova and Vladimirov 2007; Ramdani et al. 2015). The close relative of spurge laurel, Daphne mezereum L., contains the same chromosomal cytotype (Ramdani et al. 2015). Additionally, the physical chromosome length ranges from 2.0-3.0 µm (Kamari et al. 2003). However, no literature exists on the chromosomal number determined for locations in Canada. 3 https://mc.manuscriptcentral.com/cjps-pubs Canadian Journal of Plant Science Page 4 of 35 (b) Distinguishing Features Daphne is easily distinguishable from most other members of the genus by its black drupes, entire glabrescence, and reduced lateral inflorescences with 3-7 greenish-white flowers (Feliner 1996). Daphne resembles Pacific rhododendron, Rhododendron macrophyllum, with the distinct broadleaf whorls on branched stems; yet daphne does not produce bright pink flowers like Pacific rhododendron. For this reason, spurge laurel is a common gardening favourite (Invasive Council of BC 2014). Daphne laureola is furthermore differentiated from FebruaryFor Daphne Review (Daphne mezereum Only) due to the color of the fruit and deciduous leaf habit; D. laureola containing dark black drupes and entire glabrescence. The flowers of February Daphne are lilac-purple or white in clusters (Nelson et al. 2007). Daphne has been more frequently observed in shaded areas, ranging from large bushes to single juvenile stems (Lei 2014; Strelau Pers. Obs.). Refer to Figure 1 for an illustration of the unique architecture in an adult daphne plant. (c) Intraspecific variation Variation amongst D. laureola plants has led to a debate over taxonomic divisions within the species. In the western Mediterranean, three intraspecific taxa have been described. These include subspecies Philippei (Gren) Nyman from the Pyrenees and the Cantabrian Mountains, var. cantabrica (Wilik). Wilik from the upper elevations of the Cantabrian Mountains, and subspecies Latifolia (Cross.) Rivas-Mart from Southern Spain and North Africa. Also, from North Africa, D. laureola f. kabylica (Chabert) Pau from Algeria and D. laureola var. hosmariensis Ball from Morocco have been described, albeit less commonly (Feliner 1996). There also exists Daphne laureola subsp. laureola, var. laureola, var. philippei (Gren.) Meisn, and latifolia Cross. In the Baetic ranges in Spain, the central core daphne 4 https://mc.manuscriptcentral.com/cjps-pubs Page 5 of 35 Canadian Journal of Plant Science populations have a slightly higher genetic diversity compared to marginal populations (Castilla et al. 2012). An extensive range of architectural types in this species exists because of the ability to varying height, length, and degree of stem branching (Alonso et al. 2004). Studies have demonstrated variation in the concentration of coumarins (vanilla scented flavouring) (Alonso et al. 2004). Daphne laureola, as a gynodioecious species, has a higher concentration of coumarins in females and populations at higher altitudes; following optimal theory (Alonso et al. 2004). This can lead to a variationFor in sex ratiosReview depending on theOnly environment. However, the cost of male function may be context dependent (Alonso et al. 2005). Although gynodioecy and resulting sex ratios of D. laureola has not been studied in Canada, this is an important area for future research as it would improve our understanding of the evolutionary dynamics of D. laureola in its native and introduced ranges. In British Columbia there seems to be a distinction between plants growing in the sun and those growing in the shade. Plants with low irradiant sunlight generally have thinner, darker green, healthy looking leaves, whereas those growing under high irradiant sunlight have thicker, slightly down curled, chlorotic leaves (pers. Obs. J. Sargent, C. Webb). Leaves have been observed to contain higher leaf mass to area ratio (LMA) and fewer nitrogen levels in open sites compared to Douglas-fir understory locations (Lei 2014). (d) Illustrations Fig. 1 illustrates the anatomy of the plant; Fig. 2 provides some photographs to assist with the identification of D. laureola. The distribution in Canada and the adjoining Pacific Northwest is illustrated in Fig. 3. 3. Economic Importance 5 https://mc.manuscriptcentral.com/cjps-pubs Canadian Journal of Plant Science Page 6 of 35 (a) Detrimental Daphne is native to Eurasia and North Africa but has recently been introduced as an invasive plant in North America (Alonso and Herrera 1996; Lei 2014; EFlora BC 2016).