Wedelia trilobata, a plant grown for its aesthetic appeal as a groundcover, poses a significant environmental concern in many tropical and subtropical areas. Despite its widespread use in landscaping, this species has become an aggressive invader, disrupting local ecosystems. This article explores its characteristics, invasive mechanisms, ecological and economic impacts, and management strategies.
What is Wedelia Trilobata?
Wedelia trilobata, also known as Singapore daisy, creeping oxeye, or trailing daisy, is a perennial herb that spreads along the ground. It grows to a height of 20 to 30 centimeters, with rounded stems that can extend up to 40 centimeters and root at the nodes. Its leaves are arranged oppositely, fleshy and hairy, measuring 4 to 9 centimeters long and 2 to 5 centimeters wide. These leaves are three-lobed with serrated or irregularly toothed margins, appearing dark green on top and lighter underneath.
The plant produces bright yellow, daisy-like flower heads, 2 to 3.5 centimeters across, appearing singly on upright stalks 3 to 15 centimeters long. Each flower head contains 8 to 13 ray florets, or “petals,” with finely toothed tips. At the center, numerous tiny yellow tubular flowers are found. This species is native to Mexico, Central America, and the Caribbean, including parts of tropical South America.
How It Becomes Invasive
Wedelia trilobata spreads primarily through vegetative means, rather than relying heavily on seeds, which are often not fertile. Its stems readily root at the nodes wherever they touch the soil, allowing it to quickly form dense, mat-like ground cover. This rapid growth enables it to outcompete and smother native plant species by blocking sunlight and monopolizing space and nutrients. The plant tolerates a wide range of environmental conditions, including dry and moist sites, and various soil types like bare limestone or nutrient-poor sandy beaches. It also thrives in both sunny and shady locations, making it highly adaptable to diverse habitats.
This aggressive growth and adaptability have led to its classification by the International Union for Conservation of Nature (IUCN) as one of the “100 of the World’s Worst Invasive Alien Species.” Its continued availability as an ornamental further contributes to its spread into new areas, where it readily escapes cultivation.
Consequences of Its Spread
Once established, Wedelia trilobata severely impacts local biodiversity by displacing indigenous plant species. The dense mats it forms prevent the regeneration of native plants, reducing overall plant diversity. This loss of native flora affects wildlife that depend on these plants for food and shelter, disrupting the ecological balance of invaded habitats. Its dense thickets of stems, foliage, and litter can inhibit the germination and growth of other species in the soil seed bank.
The plant’s allelopathic effects, where it releases chemicals that inhibit the growth of nearby plants, also contribute to its dominance. Economically, Wedelia trilobata can affect agriculture by competing with crops for resources like nutrients, light, and water, potentially reducing crop yields. While specific economic figures are often unavailable, the costs associated with managing and controlling this invasive weed are substantial, impacting resources allocated to environmental restoration and agricultural productivity.
Managing This Invasive Plant
Controlling Wedelia trilobata infestations requires sustained effort due to its aggressive growth and vegetative reproduction. Manual removal is effective for small areas, but all plant fragments must be collected and properly disposed of, as even small stem pieces can root and form new plants. Stripping the top few centimeters of soil can also be effective, though this method is costly and requires diligent follow-up to manage any regrowth.
Chemical control methods also show promise for larger infestations. Herbicides like 2,4-D sodium salt can significantly reduce Wedelia trilobata density. This herbicide is absorbed through the foliage and stems, then translocated to the plant’s growing regions, leading to its demise. Glyphosate, another herbicide, also effectively reduces weed density. Preventative measures, such as banning its planting where it cannot be contained and prohibiting the dumping of garden waste in vacant lots, are important steps to limit its further spread.