Pretty much everything in your garden can be an invasive plant

Updated: Apr 25

Over 600 plant species, including marijuana, are considered potential threats to Guam's ecosystem


Portulaca

Portulaca, a genus of herbaceous plant that bears yellow, orange or fuchsia dainty flowers, was among the bestsellers at Tropical Blooms and Greens in Dededo. But the nursery had to stop selling portulaca because, according to the Department of Agriculture, that beauty is a beast.


“I had to pull them out of the shelves,” said Noemi Pitts, a horticulturist and owner of Tropical Blooms, which also supplies plants to Home Depot Guam. “I couldn’t imagine portulaca being an invasive plant when I don’t see them thrive in neglect around the island. If anybody throws them out in the ground without watering them, they will not survive. They will dry out and die.”


But agriculture authorities say otherwise.


​Portulaca grandiflora and Portulaca oleracea, both also known as bodulagas, botdolagas or donkulu, are among the more than 600 plant species on Guam that are listed as “invasive” or “potentially invasive” based on the Pacific Island Ecosystems at Risk project’s (PIER) profiling.

Pothos

“The removal of the portulaca was ordered by the Biosecurity Division,” said Glen Dulla, invasive species section supervisor at the Guam Department of Agriculture. “Invasive plants such as morning glories, golden pothos, horsetail ferns and other vines have been removed from retail stores in the past.”


The database for "Plant Threats to Pacific Ecosystems” includes those of environmental concern (including those that are probably of threat only to islands with high elevations) as well as agricultural and ruderal weeds. (See list here.)

While Guam is familiar with the most obvious invasive plants such as the tangan-tangan tree, chain of love, ivy gourd and morning glory, the PIER project’s database contains ornamental species that a regular gardener or plant collector would not suspect to be threats to the island’s delicate ecosystem.


Portulaca, for example, "is known to escape gardens and naturalize in the wild outcompeting native/preferred vegetation,” according to Christine Fejeran, chief of the DOAG’s Forestry Division.


Portulaca has adapted to Guam’s environment and quickly covers an area, Fejeran said. “Without its natural grazers or environmental controls of its native range they have the potential to take over an area,” she added.


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The PIER project database includes species of trees, vines, herbs and succulents that are pretty much everything you have in your home or outdoor garden, including aglaonema, alocasia, pothos, ficus, snake plant, dumb cane and begonia. The list also includes marijuana.


“People growing these invasive plants should understand the environmental consequences the escape from cultivation poses,” Dulla said. “It is a common sight to see golden pothos vines, which makes a pretty house plant, thrown out someone's backyard and strangling the adjoining forest.”


He advised gardeners not to “just throw out plant material when you trim your plants as they may be propagules that can spread.”


The PIER project said information provided in the database “is based on the supporting data and may not represent the current situation.”


“There are several databases that document known cases of plants being invasive and/or asses the risk of plants becoming invasive in our climate should they escape cultivation,” Dulla said. “Many of these plants were imported into Guam before these tools existed. We do not encourage the importation, propagation and sale of high-risk plants.”


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The agriculture department advises gardeners to grow and propagate native plant species instead.


“We understand that people want to grow exotics for various reasons, but the threat of bringing something to the island that our unique limestone forests and rare savanna species may not be adapted to defend against is very high. Introductions threaten the very system that makes life on Guam so unique,” Fejeran said.


She said non-native plant introductions have the added risk of not just the specific plant brought in, but everything that plant could be carrying such as its soil and medium containing it.


“Potential escape of the plant also means the spread of a fungus, disease and or pest that our native plants have no evolutionary defenses against,” Fejeran said.


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Dulla said the cost of management and control of invasive plants may not easy to quantify but the process also involves several agencies.


Guam Customs and Quarantine regulates the importation of invasive plants through the border. The Parks and Recreations manages invasive weeds and vines on park properties. The Guam Power Authority maintains powerlines by removing invasive vines or African tulip trees growing under the powerlines. The Department f Public Works clears large tracks of invasive bamboo to open rivers and stop residential flooding.


“These everyday costly functions are brought forth by these invasive plants that were once ornamental imports,” Dulla said.


The agriculture department has not engaged in a removal effort but Fejeran noted that education and outreach would be a critical step to promote managing green waste and exotic species on private properties. “Managing what you introduce to your yard properly and preventing the spread from your property,” she said.




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