Love and Hate – The Story of Purple Loosestrife

In the early 1800’s, seeds of purple loosestrife found their way to North America. They arrived from Europe several times by various means – accidentally embedded in the ballast of ships, inadvertently tucked in sheep’s wool, and purposely carried in the hands of humans. Native to much of Europe and parts of Asia and commonly found growing in wetlands and other riparian areas, purple loosestrife’s appealing spikes of magenta flowers, sturdy, upright growth habit, and ease of propagation made it a prized ornamental; its abundant nectar made it a favorite of beekeepers.

During its first 150 years or so in North America, purple loosestrife became naturalized in ditches, wet meadows, and the banks of streams, rivers, lakes, and ponds while also enjoying a place in our gardens. Concern about its spread was raised in the first half of the twentieth century, but it wasn’t until the 1980’s after an extensive survey was done and a special report was issued by the U.S. Fish and Wildlife Service that attitudes about purple loosestrife shifted dramatically. At that point, it was no longer a benign invader and welcome garden companion. It was, instead, a biological menace that needed to be destroyed.

Lytrhrum salicaria – commonly known as purple loosestrife, spiked willow-herb, long purples, rainbow weed, etc. – is an herbaceous perennial in the family Lythraceae. It reaches up to two meters tall; has square or angular stems with lance-shaped, stalkless leaves up to ten centimeters long; and ends in dense, towering spikes of pink-purple, 5-7 petaled flowers. The flowers attract a wide variety of pollinating insects – mostly bees – and afterwards produce small capsules full of tiny, red-brown seeds. Charles Darwin thoroughly studied the flowers of purple loosestrife; he was intrigued by the plant for many reasons, including its heterostyly (a topic for another post).

Lythrum salicaria (purple loosestrife) – image credit: wikimedia commons

Purple loosestrife seeds remain viable for up to 20 years and are transported by wind, water, and in mud stuck to the feet of birds. Apart from seeds, populations expand clonally as root crowns grow larger each year and produce increasingly more stems. Broken stem pieces also take root in mud, creating new plants. Purple loosestrife’s ability to form expansive populations in a quick manner, pushing other plants aside and forming what appears to be a dense monoculture, is part of the reason it has earned itself a place among the International Union for Conservation of Nature’s list of 100 World’s Worst Invasive Alien Species.

But is this ranking justified? In a paper published in Biological Invasions in 2010, Claude Lavoie compares news reports about purple loosestrife around the turn of the century with data presented in scientific papers and finds that the reports largely exaggerate the evidence. Purple loosestrife was being accused of all manner of crimes against nature and was being condemned before there was sound evidence to justify such actions.

It began with the U.S. Fish and Wildlife Service’s special report published in 1987. According to Lavoie, “a long list of the impacts of the species on wetland flora and fauna [was] presented,” but the claims were not supported by observational or experimental data – “the impacts [were] only suspected.” Regardless, wetland managers began campaigns against purple loosestrife in order to convince the public that it was a Beautiful Killer. News outlets were quick to spread the word about this “killer” plant. When biological control programs began in the 1990’s, news outlets reported on their success. Little empirical evidence had been published on either topic, and debates about purple loosestrife’s impacts remained unsettled in the scientific community.

The flowers of purple loosestrife (Lythrum salicaria) – photo credit: wikimedia commons

Around this time, five reviews were published examining the evidence against purple loosestrife. Lavoie reports that all but one of them “rely on a relatively high number of sources that have not been published in peer-reviewed journals.” After examining the reviews, Lavoie concludes: “although each review provided valuable information on purple loosestrife, most were somewhat biased and relied on a substantial amount of information that was anecdotal or not screened by reviewers during a formal evaluation process. Only one review was impartial, and this one painted an inconclusive picture of the species.”

Research has continued regarding the impacts of purple loosestrife, and so Lavoie examined 34 studies that were published during the 2000’s in search of conclusive evidence that the plant is as destructive to wetlands and wildlife as has been claimed. Upon examination he concludes that “stating that this plant has ‘large negative impacts’ on wetlands is probably exaggerated.” The most common accusation – that purple loosestrife crowds out native plants and forms a monoculture – “is controversial and has not been observed in nature (with maybe one exception).” Lavoie finds that there is “certainly no evidence that purple loosestrife ‘kills wetlands’ or ‘creates biological deserts,'” and “there are no published studies [in peer-reviewed journals] demonstrating that purple loosestrife has an impact on waterfowl or fishes.” All other negative claims against purple loosestrife “have not been the object of a study,” except for its impact on amphibians, which had at that time only been tested on two species, one “reacting negatively.” Certain claims – such as purple loosestrife’s impact on wetland hydrology – should be studied more in depth “considering the apparent public consensus on the detrimental effects of purple loosestrife” on wetland ecosystems.

Lavoie agrees that it is reasonable to control purple loosestrife when the intention is to reduce additional pressures on an ecosystem that is already highly threatened. However, he warns that “focusing on purple loosestrife instead of on other invasive species or on wetland losses to agriculture or urban sprawl could divert the attention of environmental managers from more urgent protection needs.” There is mounting evidence that purple loosestrife invasions are disturbance-dependent and are “an indicator of anthropogenic disturbances.” In order to protect our wetlands, we must first protect them against undue disturbance. Lavoie supports using the Precautionary Principle when dealing with introduced species; however, he finds the approach “much more valuable for newcomers than for invaders coexisting with native species for more than a century.”

A field of purple loosestrife in Massachusetts – photo credit: wikimedia commons

Purple loosestrife has found its way to nearly every state in America and most of the Canadian provinces. Peter Del Tredici writes in Wild Urban Plants of the Northeast, “Conservationists despise purple loosestrife, despite its beauty, and it is listed as an invasive species in most of the states where it grows.” By listing a plant as a noxious weed, landowners are obligated to remove it. Care must be taken though, as removal of purple loosestrife can result in a secondary invasion by noxious weeds with an even worse track record, such as common reed or reed canary grass. “Hardly a gain from the biodiversity point of view,” quips Lavoie.

Claude Lavoie’s paper and the papers he references are definitely worth reading. It is important that we continue to study purple loosestrife and species like it in order to fully understand the impact that introduced species are having on natural areas, especially since it is unlikely that we will ever completely eliminate them. On that note, I’ll leave you with this passage from The Book of Swamp and Bog by John Eastman:

The situation is easy for environmentalists to deplore. This plant, like few others, stirs our alien prejudice. Our native cattails, for example, are almost as rudely aggressive and competitive in many wetland areas as purple loosestrife. Yet, because cattails obvioulsy ‘belong here,’ they seldom evoke the same outraged feelings against their existence. … With the spread of purple loosestrife, we have new opportunities to witness the phases of an ever-recurring ecological process. We can watch it affect, change, adapt, and refit both its own elements and those of invaded communities into new arrangements of energy efficiency. The point is that we might as well study this process rather than simply deplore it; we have few alternatives.

Campaigns Against Invasive Species, part two

Happy American Wetlands Month!

One of the biggest threats to wetland ecosystems is, of course, invasive species. In last week’s post I shared a selection of videos that were produced by a variety of organizations to inform the public about invasive species. Many such videos specifically address invasives in wetlands and waterways. Here are a few of those videos.

Invasive Species of Idaho reminds you to “Clean, Drain, Dry” to avoid transporting aquatic hitchhikers:

Purple loosestrife is a “very wicked plant:”

Commander Ben vs. the Saltcedar Bandits:

Michigan’s Department of Environmental Quality urges hunters not to use Phragmites australis to make duck blinds:

More information about Phragmites by National Geographic:

Texas Parks and Wildlife and the Attack of the Zebra Mussels:

The story of Eurasian milfoil told by students at George Williams College:

Water hyacinth – another “very wicked plant”:

Water hyacinth invasion in Africa:

Attack of the Killer Algae by TED-Ed:

Tiny Plants: Duckweeds

Obviously, a series about tiny plants must begin with duckweeds – a group of aquatic plants that holds records in a number of categories including smallest flowering plants, smallest vascular plants, and smallest fruits. They are so small, in fact, that they don’t even have true stems or leaves, but rather are composed of undifferentiated vegetative tissue known as a thallus. Some species have one or a few tiny rootlets; others form no roots at all. However, what they lack in their hyper-diminutive size, they make up for in their ability to form massive colonies, creating dense mats that can take up serious square footage in a pond or lake. Depending on the species present, a single square yard of a duckweed colony can contain hundreds of thousands of individual plants.

Five genera make up the duckweed subfamily (Lemnoideae): Spirodela, Lemna, Landoltia, Wolffia, and Wolffiella. This group used to be considered the family Lemnaceae, but has since been placed in Araceae – the arum family. While they are considered flowering plants, not all species of duckweeds produce flowers, and those that do, do so only rarely. They mainly reproduce asexually through a process called budding, in which growth occurs at the base of the thallus (or frond) and eventually splits off from the parent plant. This process happens fairly quickly, which is why duckweeds are able to create substantial colonies.

 

Duckweed mats form atop the still waters of lakes and ponds, but can also form in very slow moving rivers and streams. Their presence is an indicator of high levels of minerals and nutrients, which is why they are commonly seen in agricultural and industrial wastewater ponds. Nutrients are absorbed through the underside of the thallus, so the rootlets of duckweeds likely function more for stabilization than for nutrient uptake. As duckweed mats expand and grow dense, they shade the environments below them. John Eastman writes about this phenomenon in The Book of Swamp and Bog: “Thick blankets of duckweed can shade pond bottoms, preventing adequate photosynthesis and making life difficult or impossible for submersed plants and animals…however, this is often a problem of only intermittent duration.” One potential benefit of such dense mats is that they can kill off mosquito larvae. Eastman points out that for this to be the case, the duckweed may need to be accompanied by other surface dwelling plants in order to create dense enough shade.

duckweed 1

Duckweeds overwinter by forming turions, small buds that act as storage organs. Eastman explains the process:

These tiny, kidney-shaped buds detach and immediately sink to the bottom, where they remain all winter. In the spring, each turion expels a gas bubble, which causes it to rise to the surface, where it rapidly develops into a new duckweed thallus. Turion formation requires a combination of bright sunlight and high water temperature.

Duckweeds colonize new areas either by moving downstream (if they have that option) or by finding themselves attached to the fur, feathers, or feet of animals that unwittingly transport them. The common name, duckweed, is likely derived from the fact that it is a major source of food for waterfowl. It is high in protein and rich in nutrients, especially when you factor in all the tiny critters growing on and among it. Muskrats and beavers occasionally eat duckweeds as well. Despite losses from herbivory by these creatures, being made mobile by their moving bodies is a major boon.

A collection of various duckweed species - photo credit: wikimedia commons

A collection of various duckweed species – photo credit: wikimedia commons

Duckweeds are also consumed by various species of fish, which is why they are commonly used as a food source in aquaculture. Frogs and other amphibians as well as various aquatic insects and microinvertebrates also consume duckweeds. The diversity of small animals and protists that use duckweeds and the environments they help create is incredible. Eastman writes:

Duckweed mats host a large variety of small fauna that feed, lay eggs, or shelter amid the plants. Many of them secure themselves to the thallus rootlets or undersides, where they snare and capture passing food organisms or particles. Protozoans, rotifers, insect larvae, and crustaceans are often abundant.

Humans have also been known to eat duckweeds. Duckweed farming is not a simple procedure, but a highly nutritious food source is the result when it can be done. A simpler alternative is to use the harvest as animal feed. Duckweeds are also used in bioremediation and are being considered as a source of biofuel.

Depending on the species, an individual duckweed can vary in width from 10 millimeters to less than 1 millimeter. They truly are tiny wonders of the plant world, and it is worth getting down to their level for a closer look (hand lens recommended).

Additional Resources

Field Trip: Bruneau Dunes State Park

One of the aims of American Wetlands Month is to encourage people to get out and visit nearby wetlands. I accepted this challenge by visiting the small lakes and marshes of Bruneau Dunes State Park which is located about 20 miles south of Mountain Home, Idaho (or, 70 miles from my house).

The park is known for its enormous sand dunes, claiming the tallest single-structured sand dune in North America which measures about 470 feet. The dunes began forming about 15,000 years ago during the Bonneville Flood. After the flood receded, the dunes continued to grow due to their unique location – a basin in which strong winds approach from both the northwest and the southeast, carrying sand from the surrounding steppes and keeping the dunes in place.

Two small lakes and a marsh are found nestled among the dunes, and the Snake River flows just north of the park. Apart from the dunes and the wetlands, the park also includes desert and prairie habitats and is situated in an extensive conservation area called Morley Nelson Snake River Birds of Prey. If that’s not enough, Bruneau Dunes State Park is home to a public observatory, where visitors can view the night sky and learn more about the stars and our place in the universe.

A marshy entrance to Dunes Lake

A marshy entrance to Dunes Lake

Climbing the sand dunes (and, if you’re up for it, sledding down them) is understandably a popular activity at the park. I spent a decent amount of time on top of the dunes, partly because the view was great and because the mosquitoes seemed to be absent up there. Yes, when visiting a wetland, you are advised to carry mosquito repellent, otherwise the cloud of mosquitoes that will undoubtedly surround you will make for an unpleasant experience. They will also make it difficult to stand still long enough to take a decent picture.

On top of a small dune looking across lake to large dune.

On top of small dune looking across lake to large dune

On top of large dune looking across lake to small dune.

On top of large dune looking across lake to small dune

Traversing the spine of a brontosauras (aka sand dune).

Traversing the spine of a brontosaurus (a.k.a. sand dune)

On top of the sand dune looking down at the lake and marsh.

On top of sand dune looking down at the lake and marsh

The marshes and shores around the lakes were populated with numerous wetland plants, including swamp milkweed (Aesclepias incarnata), duckweed (Lemna minuta), cattails (Typha sp.), and various rushes, sedges, and grasses. Native shrubs were also present, however the dominant woody plants were (unfortunately) introduced species: Russian olive (Elaeagnus angustifolia) and saltcedar (Tamarix chinenesis).

An entrance to the marsh

An entrance to the marsh

Flowers of bullrush (Schoenoplectus sp.)

Flowers of bulrush (Schoenoplectus sp.)

Russian olive (Eleagnus angustifolia)

Russian olive (Elaeagnus angustifolia)

Saltcedar (Tamarix chinensis)

Saltcedar (Tamarix chinensis)

Despite being there to explore and celebrate the wetland, the plants in the adjacent area (which appeared to be growing in almost 100% sand) continued to draw me away. Some I recognized easily, while others I could only identify to genus or couldn’t identify at all. Some notable observations included low lupine (Lupinus pusillus), sand-dune penstemon (Penstemon acuminatus), pale evening primrose (Oenothera pallida), and species in the genera Astragalus, Erigeron, and Eriogonum. Two bunchgrasses were particularly common throughout the area: Indian ricegrass (Achnatherum hymenoides) and needle and thread grass (Hesperostipa comata).

All of these plants are worthy of being photographed; however, the wind makes that difficult to do. Idaho is a windy state, and an area composed of wind-formed sand dunes is particularly windy. Between swarms of mosquitoes and consistent wind, capturing decent photos was a challenge. Aside from those minor nuissances, I had a very enjoyable time and hope to visit again soon.

Phacelia (Phacelia hastata)

Silverleaf phacelia (Phacelia hastata)

Nakedstem sunray (Enceliopsis nudicaulis)

Nakedstem sunray (Enceliopsis nudicaulis)

Have you visited a wetland this month? Or do you plan to? Share your adventures in the comments section below.

Happy American Wetlands Month!

To kick off this year’s American Wetlands Month, I am reposting something I posted three years ago. I have updated the links and added a few more resources. In celebration, all Awkward Botany posts in May will have something to do with wetlands. An underlying goal of American Wetlands Month is to encourage people to get out and visit wetlands in their area and find out what they can do to help conserve them. Hopefully this series of posts helps to further that aim.

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“May is American Wetlands Month! No matter where you live, chances are there’s a wetland nearby that provides important environmental benefits to your community. Wetlands support diverse fish and wildlife species, filter pollutants from rain water runoff, help recharge groundwater supplies, prevent flooding and enhance property values.” – Earth Gauge (A program of the National Environmental Education Foundation)

Wetlands are ecosystems that are characterized by their vegetation (aquatic plants), their soils (formed during anaerobic conditions caused by being flooded or saturated with standing water), and, of course, their state of being largely saturated with water either seasonally or permanently. Examples of natural wetlands include bogs, fens, marshes, and swamps. Wetlands can also be constructed by humans for the purpose of collecting storm water runoff from urban areas in efforts to reduce the risk of flooding and avoid overwhelming municipal sewer systems during large rainstorms.

Wetlands are the most threatened type of ecosystem on earth, and we are losing them at a steady clip. Major threats to wetlands include land development, pollution (agricultural, commercial, residential, etc.), and the introduction of invasive species. Considering the benefits we receive from having wetlands around, it is imperative that we protect them. Earth Gauge offers some suggestions on how to do so.

wetland benefits

Speaking of wetlands, one of my favorite wetland plant species is marsh marigold (Caltha palustris). It is in the buttercup family (Ranunculaceae) and is common throughout the Northern Hemisphere. I became familiar with this plant when I was volunteering at a wetland in Edwardsville, IL. Perhaps you’ve seen it growing near you.

Marsh Marigold (Caltha palustris) - Photo taken at Idaho Botanical Garden.

Marsh Marigold (Caltha palustris) – Photo taken at Idaho Botanical Garden.

Additional Resources