Larry Maupin is a freelance garden writer and photographer
from Dallas, Texas. A frequent contributor to gardening and water
gardening magazines, he is a member of the Garden Writers Association.
This excellent article and photos (Copyright Larry Maupin
2003 All Rights Reserved) are reprinted here with permission.
"possibly the worst weed in the
THE ALIENS ARE COMING!
RESPONSIBLE WATER GARDENING WITHOUT INVASIVES
By Larry Maupin - Click images to
They are arriving quietly everyday. Alien invaders are coming,
not from distant worlds across the universe but from foreign
countries and climates to invade our garden worlds. They're not
little green men, but rather little green plants, seeking sun,
soil and sustenance. This silent invasion has been going on for
centuries, but with the acceleration of modern travel and our
demands for "new" plants, the aliens are arriving at
an increasingly alarming rate.
Many of our favorite garden and aquatic plants and tropical
fish originated in tropical countries with climates very different
from our temperate United States. That¹s much of their charm
for us, for their tropical beauty adds greatly to our garden
experience. However, there is a growing concern among those who
have taken up the responsibility to protect our natural environment
from harm. Various fisheries biologists, aquatic plant researchers
and others have observed and reported the damaging effects that
some fast-growing exotic plants can have if they "escape"
into the wilds of our country.
A FEW DEFINITIONS
While the vocabulary used in the invasive plant debate continues
to evolve, some terms are commonly used and understood.
Native - A plant or animal that is naturally found in
wild areas within a certain region, which can be a small local
area or an entire continent. For example, "Giant salvinia
(Salvinia molesta) is native to South America."
Indigenous - A plant or animal whose natural habitat is
found only within a defined area. For example, "Purple loosestrife
(Lythrum salicaria) is indigenous to Australia, but is
banned in 23 of our 50 United States."
Exotic - Any plant or animal imported from another area.
For example, "Except for their native plant displays, most
nurseries offer only exotic plants, ranging from the amur maple
tree (Acer ginalla) to zoysia grass (Zoysia tenuifolia)."
Introduced - Any exotic plant or animal that is brought
in from another area and placed in the wild. For example, "Kudzu
(Pueraria lobata) was introduced to the South by railroad
barons to control erosion along newly built railroads."
Escaped - A cultivated plant or animal for use in gardens
and landscapes that has propagated itself and flourished in wild
areas, often becoming invasive. For example, "English Ivy
(Hedera helix) is a popular hardy vine for the landscape
except in the Pacific Northwest, where it has escaped into
the wild and become classified as a destructive weed."
Naturalized - An escaped plant or animal that becomes
established in the wild but is not invasive. For example, "Giant
reed grass (Arundo donax) was introduced on the West Coast but
now is naturalized from California to Kentucky."
Invasive species - According to the Executive Order 13112,
signed by then-President Bill Clinton on February 3, 1999, an
"invasive species" is defined as "a species that
is 1) non-native (or alien) to the ecosystem under consideration
and 2) whose introduction causes or is likely to cause economic
or environmental harm or harm to human health."
A popular definition of a weed is any plant that is growing
where you don't want it. Most folks would not consider the southern
live oak (Quercus virginiana) to be a weed, but if you
have hundreds of deeply rooted acorn seedlings in your groundcover
bed, you would definitely call them weeds.
So it is with many plants on the various state and Federal "invasive
species" lists. One man's treasure becomes another man's
trash. One blooming water hyacinth is lovely in a small pond;
thousands in a lake or stream can destroy an ecosystem or a livelihood.
Schefflera (Brassaia actinophylla), which most people
know as a popular houseplant, is a Category I (worst type) invasive
in Florida. Butterfly bush (Buddleja) is often hard to
maintain in the Southwest U.S., but it is taking over disturbed
soil areas in the East. English ivy (Hedera helix) is
the pride and joy of the American Ivy Society, "Dedicated
to the Education and Promotion of the genus Hedera," which
is located in Naples, Florida; the same plant is very unpopular
in the Pacific Northwest due to the destruction it is causing
Besides plants, exotic fish and shrimp pathogens and parasites
have been introduced into the United States on infected stock
for aquaculture. Crates and containers can harbor snails, slugs,
mollusks, beetles and microorganisms. Military cargo transport
also brings in harmful species, such as the Asian gypsy moth
and brown tree snakes. Some invasives even make the evening news,
including zebra mussels, imported fire ants, and Africanized
honey bees. We've grown familiar with dandelions and crabgrass
- two that were imported with the best of intentions.
UNDERSTANDING THE PROBLEM
This is not a new problem for America or for the rest of the
world. To keep this in perspective, understand that not all introduced
or exotic plants have proven to be harmful. In fact, most are
beneficial, providing food, medicine, colorful flowers or attractive
foliage. Of an estimated 50,000 plant introductions to the USA,
less than five percent have become established in the wild. Of
these only three-tenths of one percent are considered to be causing
harm. Despite the relatively small percentage of introductions
becoming problematic, the extreme severity of the problems that
they can lead to should not be under-estimated. For example,
in the sub-tropical state of Florida, over 240 million taxpayer
dollars have been spent in trying to control invasive plants
over the past 20 years.
Providence, Rhode Island's Brown University Office of Technology
Assessment has analyzed the economic impact of invasive species
in the United States; they report that "invasive species
have cost $97 billion dollars in the United States from 1906
to 1991." In 1999 Dr. David Pimentel et al reported that
annual losses due to invasive species now cost us over $138 billion
dollars per year. Pimentel et al's figure only includes economic
damages and control costs, not environmental and health costs.
That translates to costing roughly $575 per year for every man,
woman and child in America!
While Florida's warm climate and long growing season makes
it ripe for the ravages of invasive species, no state is immune.
In fact, every state has developed its own list of invasive species,
WHAT MAKES A PLANT "INVASIVE"?
The worst weeds are classified as "invasive," but what
makes one plant invasive and another not? Most non-native plants
introduced to new areas by humans do not cause environmental
problems. And yet, this one question fuels much of the controversy
surrounding the invasive plant issue.
Another definition describes an invasive species as one that
is capable of reproducing offspring rapidly at considerable distance
from the parent and offers the rule of 6 miles in three years
and 100 miles in 50 years as a guide. We know that floating aquatic
plants in river systems can far exceed this guideline, which
makes them some of the worst weeds in the world.
It appears as just another water plant, floating
loosely and freely (it is a true floater). It multiplies very
rapidly in warm, nutrient-rich, still water.
As the population grows, it spreads over the
water until the surface is
covered. At this point is begins to increase in depth and may
become up to two feet thick due to wind and wave action.
As the population becomes more dense, the form
of the plant changes from a flat set of leaves to an upright
form with undulating layers of foliage, as shown in the close-up
photo at the top of the page.
Consider the effects of just one invasive plant, giant
salvinia (Salvinia molesta). There are other "baddies,"
like water lettuce (Pistia stratiotes) and water hyacinth
(Eichhornia crassipes), but giant salvinia is the newest
and baddest bully on the block. It is technically an aquatic
fern native to the river systems of southern Brazil. From there
it has spread to South Africa, Australia and the United States.
The U. S. Army Corps of Engineers' Aquatic Plant Control Section
in Jacksonville, Florida believes the plant "was most likely
introduced through the aquarium and landscape trades." Many
folks enjoy their plants and fish until they are no longer able
to care for them, then they decide to "set them free."
Dr. R. Michael Smart, head of the U. S. Army Corps of Engineers'
Aquatic Ecosystem Research Facility in Lewisville, Texas provides
a succinct alternative: "Don't dump what you are tired of
- destroy it." With no native predators or pests to check
their growth, giant salvinia and other aquatics can spread quickly.
Invasive species use up nutrients that other species rely
on, and their rampant vegetation blocks sunlight and destroys
fragile environments. Fish won't eat it and it forms dense mats
of foliage that choke out other aquatic plants. Wind and wave
action can cause it to form mats up to three feet thick; then
when the thick mats die of starvation, the decaying plant material
robs the water of oxygen, killing all aquatic creatures.
Excess vegetation also ruins the waterway for recreation, fishing
and navigation, while the pond or lake takes on the look of newly
mowed pasture - acres of greenery.
Giant salvinia has been called "possibly the worst weed
in the world" due to its aggressive growth -- it can double
in quantity every 2.2 days under ideal conditions. That means
that one plant becomes 8000 in 30 days! (Don't believe it? Do
the math.) In two months the number is in the millions - clearly
not a plant you would want roaming free in your waterways.
Thriving ecosystems can be reduced to monocultures of giant
salvinia. In much of the world it is known as Karaba weed, for
it inundated the entire Karaba Lake in Zimbabwe, Africa, within
only a few years. Can you imagine a single species of floating
plant covering 96 square miles of water? So, throwing an aquatic
plant into a stream is akin to tossing a Styrofoam cup out of
a car window, except that the cup can grow to 8000 cups in a
month. And each of them can produce 8000 more!
Typical methods of controlling invasive aquatics in the wild
include mechanical harvesting, pesticide application and biological
controls. Floating equipment designed to remove vegetation is
slow and expensive to operate, and the plant material must be
disposed of somewhere - another expense. Pesticide applications
are expensive and controversial, and they are not always 100
The last option offers some hope, at least for controlling
giant salvinia. Researchers seek insects, fungi or other organisms
that will infect or damage the offensive species and cause its
death. Possible biological controls for giant salvinia include
the use of a Brazilian native called salvinia weevil (Cyrtobagous
salviniae); initial tests have been encouraging.
Because of the extensive environmental damage and huge cleanup
expenses involved, legislation has been developed to reduce or
prevent more damage. Executive Order 13112 also created the Invasive
Species Council. Its goal is to reduce or eliminate the opportunity
for exotic, or "non-indigenous," plants to escape.
Part of the effort to reduce damage involves restricting the
possession, sale or shipment of certain plants in certain states.
There is a federal invasive plant list, maintained by the
U.S. Department of Agriculture, that covers all 50 states, and
each state can prepare its own list as it sees fit. In fact,
every governing body in the country, including counties and municipalities,
seems prone to publishing their own invasive species list with
accompanying laws and fines. Included on the Federal list are
a number of woody trees and shrubs, herbaceous and aquatic plants
and many types of fish, birds and other animals. Even some insects,
snails and fungi are listed. While the invasive plant lists are
constantly evolving, they do represent the worst known offenders
- the ones that cause the most damage.
The National Aquatic Invasive Species Act may be law by the
time you read this. Its sweeping guidelines will have a major
impact on safeguarding our waterways, or restrict your access
to new varieties, depending on your opinion in this matter. If
you think this invasive plants stuff is nonsense, consider this
possibility: you arrive at your favorite park to find a new sign:
"Permanently closed to the public due to infestation of
the venomous Brown Tree Snake."
LINKING ECOLOGY AND HORTICULTURE
In December 2001 experts from across the globe met in St. Louis,
Missouri, to explore and establish workable voluntary approaches
for reducing the introduction and spread of non-native invasive
plants. The Workshop on Linking Ecology and Horticulture to Prevent
Plant Invasions was convened by the Missouri Botanical Garden
and the Royal Botanic Gardens, Kew. This historic conference
brought together for the first time some of the most respected
leaders in their fields.
The fruits of their labor are significant. Rather than furthering
the science of invasive plant management and control, which is
occurring in various scientific communities all over the world,
they took a broader view -- looking at the problem from the viewpoints
of government, educators, researchers, landscape professionals
and gardeners. Their joint efforts resulted in these findings:
1. People are the major distributors of plants.
2. The magnitude of this distribution is unprecedented and has
allowed dispersal of species that manifest aggressive traits
in new areas.
3. Plant introduction and improvement are the foundation of modern
agriculture and horticulture, yielding diversity to our supply
of plants used for food, forestry, landscapes and gardens, medicinal
and other purposes.
4. A small proportion of introduced plant species become invasive
and causes unwanted impacts to natural systems and biological
diversity as well as economies, recreation, and health.
5. Plant species can be invasive in some regions, but not in
6. The impacts of invasive plant species can occur at times and
places far removed from the site of introduction.
Then the workshop members laid out plans of action for each
of the involved segments of the ornamental horticulture/gardening
community. They determined that, "Codes of conduct for specific
communities of interest are an essential first step in that they
encourage voluntary initiative, foster information exchange,
and minimize the expense of regulation."
WHAT NURSERY PROFESSIONALS ARE DOING
A draft for the voluntary code of conduct for nursery growers
dealing with invasive species has been nearly finalized. It was
drafted at the meeting in St. Louis, and is being OK'd by university,
environmental group and governmental representatives.
The preliminary codes they adopted for themselves include
evaluating the invasive potential of introduced species, developing
and promoting suitable alternatives, phasing out existing stocks
of invasive species in their regions, following all laws on importation
and quarantine of plant materials and encouraging customers to
use noninvasive plants.
VOLUNTARY CODES OF CONDUCT FOR THE GARDENING PUBLIC
The Workshop on Linking Ecology and Horticulture to Prevent Plant
Invasions also formulated a Voluntary Code of Conduct for gardeners:
1. Seek information on which species are invasive in your
area. Sources could include botanical gardens, horticulturists,
conservationists and government agencies. Remove invasive species
from your land and replace them with non-invasive species suited
to your site and needs.
2. Do not trade plants with other gardeners if you know they
are species with invasive characteristics.
3. Request that botanical gardens and nurseries promote, display
and sell only non-invasive species.
4. Help educate your community and other gardeners in your area
through personal contact, and in such settings as garden clubs
and other civic groups.
5. Ask garden writers and other media to emphasize the problem
of invasive species and provide information. Request that garden
writers promote only non-invasive species.
6. Invite speakers knowledgeable on the invasive species issue
to speak to garden clubs, master gardeners, schools and other
7. Seek the best information on control of invasive plant species
and organize neighborhood work groups to remove invasive plant
species under the guidance of knowledgeable professionals.
8. Volunteer at botanical gardens and natural areas to assist
ongoing efforts to diminish the threat of invasive plants.
9. Participate in early warning systems by reporting invasive
species you observe in your area. Determine which group or agency
should be responsible for reports emanating from your area. If
no 800 number exists for such reporting, request that one be
established, citing the need for a clearinghouse with an 800
number and website links to information about invasive plant
10. Assist garden clubs to create policies regarding the use
of invasive species not only in horticulture, but also in activities
such as flower shows. Urge florists and others to eliminate the
use of invasive plant material.
SUCCESS IS ACHIEVABLE
Successful control of the green invaders can restore degraded,
invaded habitats. For example, volunteer workers in Oregon eliminated
diffuse knapweed from wooded hillsides and open grassland areas
that are home to over 300 native plant species. Meanwhile, removal
of alien grasses from Lanphere Dunes Preserve in California naturally
restored native plant cover! Early reporting and quick response
resulted in the complete removal of giant salvinia from a pond
in north Texas. Conservation takes time, effort and good planning,
but it works!
Garden clubs and educators are getting the word out. For example,
The Invasive Weeds Awareness Coalition held a week-long series
of events and activities in Washington, D.C. during the fourth
annual National Invasive Weeds Awareness Week in February of
this year. Education is a huge part of the solution.
WHERE TO GET THE LATEST INFORMATION
As this topic evolves, it will be increasing important for responsible
gardeners to find and follow the latest information and recommendations
of acknowledged experts. It is important to get information specific
to your area, because, as we've seen, general blacklists don't
always work. Two of the best sources include your local Agricultural
Extension Agent's office. The other is your local native plant
society. Every area has its native plant groups where the natives
versus exotics issue is always hot.
Discuss invasives with your aquarium and pond supplier. Water
hyacinth and water lettuce are popular for biofilters, but virtually
any aquatic plant can perform a similar function. Ask about alternatives
-- there are many. A great place to start is with native species.
You might be surprised at the diversity of native aquatics in
ON THE WEB
Good sources for info on the web include the Federal sites, http://www.invasivespecies.gov/
Don¹t miss the University of Florida's Center for Aquatic
and Invasive Species at http://aquat1.ifas.ufl.edu/. The Missouri
Botanical Gardens' site is another good resource: http://www.mobot.org/invasives/.
Over zealous legislation may blacklist species that are vigorous
but not truly invasive; so more research, if funding is provided
in our weak economy, can help the decision-making process for
legislators. We're already spending the money on controls - let's
spend it more wisely on prevention. As Dr. Smart said, "I'll
give you water hyacinth if I have to, but we've got to stop giant
salvinia." More plant thugs are surely on the way. Now is
the time for informed aquarists and water gardeners to study
the issues in their states and get involved in the solutions.
The keyword is LOCAL. What's best or worst in your region
may be the opposite in another. "Think globally -- act locally"
was never truer than with the invasive species issue.
QUICK TIPS FOR RESPONSIBLE WATER GARDENING
1. Learn about the problem plants and animals in your area. Your
state's parks and wildlife department keeps an official list,
and your favorite fish dealers and aquatic nurseries should know
the list also.
2. Be especially careful if building a pond near natural waterways
to prevent aquatic plant and critter escape.
3. Do not forget that wind, streams or even rainwater drainage
systems can send weed seeds far from your home, into wild habitats!
4. Never release plants or fish into the wild to "set them
free." Give them to a water gardening friend, pond dealer
or aquarist. They'll appreciate the gift.
5. Lastly, be aware - fines are stiff. Keeping or releasing the
wrong plants can be bad news for you, for the environment and
for the government agencies that have to round up the escapees.
Copyright Larry Maupin 2003 All Rights Reserved
& Marginal Plants Index of Images
With Invasives Noted