Wedelia (Sphagneticola Trilobata) - Daisy Invader of the Pacific Islands: the Worst Weed in the Pacific?

Wedelia (Sphagneticola trilobata) - Daisy invader of the Pacific Islands: The worst weed in the Pacific? Randolph R. Thaman, Professor of Pacific Islands Biogeography, the University of the South Pacific, Suva, Fiji Islands [email protected] ABSTRACT or Bay Biscayne oxeye (after Biscayne Bay near the southeast tip Can a pretty daisy be compared with the likes of the of Florida, where it grows profusely and is considered a noxious Anopheles mosquito, the dreaded malaria vector; the brown weed). tree snake that has brought birds and lizards in Guam to Wedelia is native to, and wide ranging throughout tropical extinction; or fire ants that threaten endemic lizards and cause America, where it is found from Mexico to Panama in Central blindness in dogs in New Caledonia? I think so. “Wedelia”, America, in western and northern South America (Peru, Ecuador, creeping oxeye, or the trailing daisy, formerly known as Bolivia, Columbia, Venezuela, the Guianas and Brazil), Wedelia trilobata, but now as Sphagneticola trilobata, a throughout the Caribbean (USDA GRIN 2008), and possibly deceptively beautiful, bright emerald-green creeper with Florida (Macoboy 1986), It is now cultivated throughout much of bright yellow daisy-like flowers, is one of the world’s most the tropics and subtropics as an ornamental groundcover. It is aggressive weeds and listed among the worlds 1000 worst closely related to the widespread tropical strand plant or beach invasive alien species. Native to tropical America from Mexico daisy, Wollastonia biflora (formerly known as Wedelia biflora), a to Brazil and throughout the Caribbean, wedelia is now very important medicinal plant found throughout the Pacific. cultivated, firmly established and has escaped from cultivation Interestingly, the Hawaiian endemic genus Lipochaeta is scarcely throughout the tropics and subtropics and in most of the main distinct from Wedelia genetically, and two sections of Lipochaeta islands of Polynesia, Micronesia and Melanesia. Wedelia is appear to have been independently derived from Wedelia-like out-of-control on the atolls of Kiribati, Tuvalu, Tokelau and ancestors (Wagner et al. 1990, Rabakonadrianina and Carr 1981). the Tuamotus and the limestone island of Niue; and has Wedelia is a creeping, mat-forming perennial herb with fast- rampantly spread into grazing areas, national parks, growing, rounded stems up to 40 cm long or longer that root at conservation areas, sensitive offshore islands, mangroves, the nodes and grow upwards (ascend) when flowering. The swamps, towns, villages, and along rivers, coastlines and roads attractive, bright shiny emerald-green, somewhat fleshy, leaves are in Fiji, Palau, Pohnpei, Tahiti, New Caledonia and Papua New regularly toothed on the margins, commonly with three shallow Guinea. Most attempts to control or eradicate it have failed, lobes (hence the name trilobata). The single attractive bright- some at considerable cost. It is suggested that wedelia should yellow daisy-like flowers are borne on the end of terminal and be immediately declared a serious noxious weed, should be axillary stalks. The fruit, which is rarely seen in the Pacific, is a 2- restricted from introduction into new islands and habitats, to 4-angled achene, with short, narrow pappus scales on the top and, where possible, eradicated from islands, habitats where it (Whistler 1995). Although seedlings have been observed in is yet to gain a firm foothold. If action is taken NOW, islands Hawai’i, cultivated plants seem to develop few flower heads with and communities throughout the Pacific can prevent the mature fertile seeds. Wagner et al. (1990) suggest that: “If a fertile spread of Wedelia BEFORE it replaces extensive areas of strain develops this species could become a serious pest.” indigenous, where it out-competes plants of considerable ecological and cultural importance. This conclusion is based on It already is!! And, as suggested above, it has been listed in the my studies of Wedelia over the past 30 years in most of the French Fondation TOTAL-funded Global Invasive Species countries and territories of the Pacific. Database’s “One Hundred of the World’s Worst Invasive Species”, alongside some of the world’s most notorious invasive organisms, which include: the Anopheles mosquito, the dreaded Keywords malaria vector found in Vanuatu, Solomon Islands and Papua Weedelia, invasive, weed, Pacific. New Guinea; the brown tree snake (Boiga irregularis), which, since accidental introduction into Guam from Solomon Islands 1. INTRODUCTION near the end of World War II, has brought to extinction most of Wedelia, now known officially by the scientific name, the indigenous and endemic birds and devastated the gecko and Sphagneticola trilobata (L.) Pruski (USDA-GRIN 2008), but still skink populations of Guam; miconia, the “green cancer” (Miconia widely known by its previously accepted name, Wedelia trilobata calvescens), the small tree that has invaded and devastated native (L.) Hitch.), is a member of the family Asteraceae (formerly forests in Tahiti; African tulip tree (Spathodea campanulata), Compositae), the sunflower or daisy family. The most widely used which has invaded croplands and secondary forests in Fiji; goats, common name in the Pacific is “Wedelia” (after its former genus), cats, rats, mongoose, pigs, deer, macaque monkeys and the although in Australia it is known as “Singapore daisy”, in spite of bushtail possum, all of which have caused havoc on islands its tropical American origin. Other common names include throughout the world; the Dutch elm disease fungus (Ceraticystis trailing or creeping daisy, water zinnia, rabbit’s paw and creeping ulmi), which has wiped out the totemic elm tree in North America; the Indian mynah bird (Acridotheres tristis), which has spread so and its characteristics described in reasonable detail in the revised widely and is such a nuisance in the Pacific; the rosy wolf snail 1986 edition. (Euglandina rosea), a carnivorous snail responsible for the In Fiji, well-known horticulturist and owner of “Flower Power extinction of endemic land snails in French Polynesia and Nursery” and landscaping company, Maureen Southwick, believes Hawai’i; banana bunch-top virus, which crippled export banana it was first planted as an ornamental groundcover at Suva Point in production in the Pacific; and avian malaria (Plasmodium the mid-1970s by a Mrs. Murray. Interestingly, when Mrs. Murray relictum), the micro-organism widely held responsible for the generously gave her some cuttings to plant in her well-known extinction of endemic birds in Hawai’i (ISSG 2008). Yes, this show garden, the long-time Fijian gardener looked at the cuttings pretty little ground-hugging daisy is among these monsters of the and quickly and firmly remarked that this was a weed that should invasive world! not be planted, and quickly destroyed the intended gift as a potential invader!! 2. THE INTRODUCTION OF WEEDELIA INTO THE PACIFIC ISLANDS 3. CURRENT STATUS IN THE PACIFIC The introduction of Wedelia into the tropical Pacific Islands, ISLANDS where it is now widely cultivated as a groundcover and Wedelia has been successfully introduced into most Pacific Island ornamental, seems to be a relatively recent phenomenon. Whistler countries and territories and is now widely cultivated as an easy- (1995) suggests that it was first recorded from the Pacific Islands to-maintain attractive, vigorously growing groundcover. It is in Hawai’i sometime before 1965. It is described in Neal’s In commonly planted in extensive plots and planting boxes at tourist gardens of Hawaii (1965), although no information is given resorts, as landscaping around airports, golf courses, cemeteries, regarding its date of introduction or status as a naturalized government buildings, schools and universities, office blocks and species. It is not listed in Stone’s Flora of Guam (1970), Moore other buildings in towns, on road cuts and river embankments to and McMakin’s Plants of Guam (1979), Smith’s Flora Vitiensis control surface erosion and as landscaping, along road verges and nova (1990), Parham’s Plants of the Fiji Islands (1972), or Merlin in central dividers along roads and highways, around trees in et al.’s 1992 study of the Plants of Pohnpei, despite the fact that it parks and lawns, in houseyard gardens, and occasionally as a pot is now widely naturalized and invasive in all these islands. plant. Whistler (2000) in his Tropical Ornamentals says that it is Similarly, it is not listed as present in Tonga inYuncker’s Plants preferred as a groundcover “since it is able to crowd out nearly all of Tonga (1959), where it seems to be naturalized and spreading, other herbaceous species” and “does well in coastal situations and and in Sykes’ Contributions to the flora of Niue (1970), where it large planters, and can be grown in elevated containers so that its seems to have only been introduced in the past few years, but is flowering stems hang down in yellow cascades.” now the focus of a very expensive, apparently unsuccessful, control program. Owing to its vigorous vegetative reproduction and wide environmental tolerance, the frequent pruning and disposal of its It was listed as present in Guam, on Yap in the Federated States of cuttings, and its ability to float and withstand saltwater, Wedelia Micronesia, and on Kwajalein and Enewetak Atolls in the has escaped from cultivation and become naturalized and invasive Marshall Islands by Fosberg et al. (1979), by Lambertson (1982) in most Pacific Island countries and territories, including in her study of the plants of Eniwetak, and by Thaman et al. continental islands, recent volcanic islands, limestone islands, (1994) in their Flora of Nauru. Fosberg et al. (1979) report that by atolls and small uninhabited offshore islands, often colonizing the end of the 1970s it was present in Palau where it had come to areas from the high tide mark to up elevations of 700 m or more in be known by the name ngesil ra ngebard (“the foreign Wollastonia Fiji and to 1400 m in Tahiti (PIER 2003).

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