Monthly Archives: July 2010

Piehl’s Dye Experiment and Implications for Herbicide Treatment

Are you sure you want to apply herbicide to this plant?I never thought about this when applying herbicide to cut woody vegetation, or even herbaceous weeds, but we should be watching out for nearby parasitic and hemiparasitic plants. Wood-betony (Pedicularis canadensis), for example, taps into relatives of a number of species we’re often trying to suppress or eliminate from ecological restoration projects (e.g., aspen, cedar, honeysuckle, maple, pine, sumac). Martin Piehl’s techniques for studying the relationship between hemiparasites and host plants included tracer experiments where he applied a water-soluble dye to cut trees and watched for its appearance in nearby hemiparasites. “After several days, in the case of the aspen host, a high enough concentration of dye was taken into the leaves of the parasite to cause them to wither and die …” Granted, he was applying a large amount of the chemical. But it is certainly worth keeping in mind. Fortunately, most of the invasive plants I’ve had to apply herbicide to are far from our wood-betony colony.

If anyone has personal experience with this, please let me know. I’d also like to compile a list of parasites and hemiparasites found in Wisconsin. I was actually surprised when I first learned wood-betony is a hemiparasite. There could be another parasite or hemiparasite connected to the honeysuckle (Lonicera spp.) I intend to cut and apply herbicide to later.


Piehl, MA. 1963. Mode of attachment, haustorium structure, and hosts of Pedicularis canadensis. American Journal of Botany 50(10): 978-985.


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Wood-betony and the Art of Preserving Ecological Communities

Wood-betony Rosette

Wood-betony rosette.

The wood-betony (Pedicularis canadensis) plants colonizing the lightly vegetated sandy ground left behind by construction of a septic drain field years ago appear to be simple opportunists. But this species isn’t simply exploiting an opening here and an opening there. Each rosette of feathery green leaves is paving the way for more of its own kind, and more than a few other species as well.

Wood-betony—which is found in dry to mesic prairies, savannas, and forests throughout much of Wisconsin—is a hemiparasite. It contains chlorophyll and can live as an autotroph, like other photosynthetic organisms, or it can extract organic carbon, nitrogen, and additional useful chemicals from other plant species. Some hemiparasites are very choosy, relying on one or a few host species. Others are generalists. Plant taxonomist Martin Piehl discovered that wood-betony can tap at least 80 different plant species in 35 families and occasionally latches onto other wood-betony plants as well. A random selection of victims you might recognize include Achillea millefolium, Allium cernuum, Aster laevis, Equisetum arvense, Rhus hirta, Rudbeckia hirta, and Trillium grandiflorum. Wood-betony accomplishes this by means of haustoria that develop along lateral roots and establish connections with the host plant’s roots. This occurs very early during seedling development, and water from hosts is likely essential for survival of young wood-betony growing in dry sandy soil—something to keep in mind if you scatter its seeds in your prairie, savanna, or even your perennial garden.

Hoary Puccoon and Wood-betony

Hoary puccoon (left) and wood-betony (right).

What does wood-betony acquire from this relationship? There are the basic products of photosynthesis. There are minerals. There’s water. And there are alkaloids. Alkaloids? No one has looked at Pedicularis canadensis, but chemical analysis of tissue from five other Pedicularis species consistently revealed the presence of alkaloids also found in the host plant’s roots. This could be a general feature of the genus and raises interesting ecological questions. Alkaloids exhibit potent biological effects—often deadly—and can protect plants from insects or other herbivores, including humans. Can hemiparasites commandeer alkaloids for their own protection? Biologist Lynn Adler demonstrated just this by growing Texas paintbrush (Castilleja indivisa), a southern relative of our local Castilleja species, alongside “bitter” and “sweet” varieties of lupine. Texas paintbrush plants parasitizing “bitter” lupines, which contain high levels of alkaloids, were far less prone to insect damage and produced more viable seed.

What are the implications for preserving hemiparasitic plant species, especially generalists? For each species, it isn’t just a matter of securing a host, but identifying the appropriate host—or combination of hosts—to ensure the plant is prepared to resist the local array of insect and mammalian (e.g., deer) pests. There’s also a serious lesson here for herbalists. The value or safety of a plant could depend on where it is growing. For example, though wood-betony is classified as a medicinal plant, you probably don’t want to consume wood-betony growing near Senecio vulgaris; this introduced host’s roots contain potent alkaloids that cause hepatic necrosis.

Wood-betony also acquires an indirect benefit from its relationship with host plants. By weakening the competition—by diverting resources—this generalist can suppresses the growth of other plants and opens up the canopy for itself and its comrades. Ecologists noticed a tendency for wood-betony to grow alongside relatively shorter populations of certain grasses and forbs, but there was the question of which arrives first, the wood-betony or the shorter competitors. It could simply be soil conditions. But research by Andrew Hedberg and others of Illinois State University clearly showed wood-betony reduces the above-ground growth of plants such as tall goldenrod (Solidago canadensis) and big bluestem (Andropogon gerardii). Not all species studied were affected, but it is clear wood-betony can shift the balance of power on a patch of prairie sod.

Wood-betony Fruit

Dry wood-betony fruit.

This is where the hemiparasite starts contributing to and building a richer prairie or savanna plant community. By opening the canopy for itself, wood-betony inadvertently opens the canopy for others and promotes biodiversity. The researchers who demonstrated that wood-betony can suppress competition also discovered a positive correlation between wood-betony and species diversity. Three years earlier, Wisconsin DNR researcher Richard Henderson—based on observation and experiment—had suggested that wood-betony is one of several important keystone species that preserve Midwest prairie diversity. Introduction of the seed into a small established planting was followed by a substantial decline of dominant grasses and the appearance of fourteen native forbs. Richard Henderson pointed out that other factors might have contributed, but his call for further study deserves repeating. The right mix of plant species—as far as restoration and conservation are concerned—can set the stage for success or failure.

Wood-betony might exert influence on a plant community by another, distinctly different and a bit more distant, means. The biologist Terence Laverty showed that mayapple (Podophyllum peltatum) fruit set and seed set were higher for colonies less than 25 meters—versus 50 meters—from flowering wood-betony. Mayapple doesn’t produce nectar, though most colonies are self-incompatible clones and rely on native nectar-seeking bumble bees for cross-pollination. Wood-betony, however, produces bountiful nectar and bumble bees love it. The result is a four-fold increase in the number of bumble bee visits to mayapple growing near wood-betony colonies and a corresponding 22-79% increase in fruit set and 27-42% increase in seed set. Whether mayapple benefits from other magnet species requires further research. And whether wood-betony promotes pollination of other plant species, especially host species, also requires further research.

What are the implications for restoration and conservation? Again, the right mix of plant species—including appropriate magnet species and those that rely on them—could set the stage for success or failure.

Wood-betony—a hemiparasite that might derive alkaloids from its hosts, can suppress the growth of some species, encourages the growth of others, and enhances pollination for a species that relies on bumble bees but has nothing to offer them—shines a light on a few of the nuances of preserving ecological communities. The loss of a species that prevents other species from overwhelming a community is essentially loss of the entire community. This is important to keep in mind when deciding where to focus our efforts.

Learning about the factors that contribute to building an ecological community is reward enough to justify looking for subtle variations across the landscape. However, I also have to wonder whether restoration ecologists can exploit some the described natural processes. I’m always alert for ways to work with nature, ways to temporarily harness a natural process to achieve a goal. Are there circumstances where wood-betony, or other parasites and hemiparasites, might serve on the front line against infestations of aggressive exotic plants? Richard Henderson’s simple experiment revealed there are powerful tools available if we’ll invest time in looking for them. This is where the citizen scientist can play an important role, especially given the difficulty of funding botanical and ecological research. As you enjoy the natural world, look for variations in plant communities that suggest one species is preventing another from overwhelming the whole. Do you see greater fruit and seed set when certain species appear together? Share your observations with others. Test your hypotheses. You could help find an affordable alternative to the expensive weapons—in terms of labor, machinery, toxic chemicals, and energy—currently deployed against the onslaught of invasive exotic plants.


Adler, LS. 2000. Alkaloid uptake increases fitness in a hemiparasitic plant via reduced herbivory and increased pollination. The American Naturalist 156(1): 92-99.

Hedberg, AM, VA Borowicz, and JE Armstrong. 2005. Interactions between a hemiparasitic plant, Pedicularis canadensis L. (Orobanchaceae), and members of a tallgrass prairie community. Journal of the Torrey Botanical Society 132(3): 401-410.

Henderson, RA. 2002. Are there keystone plant species driving midwest prairie diversity. In: Foré, S (ed.), Proceedings of the 18th North American Prairie Conference, Truman State University Press, Kirksville, MO.

Laverty, TM. 1992. Plant interactions for pollinator visits: a test of the magnet species effect. Oecologia 89(4): 502-508.

Piehl, MA. 1963. Mode of attachment, haustorium structure, and hosts of Pedicularis canadensis. American Journal of Botany 50(10): 978-985.

Schneider, MJ, and FR Stermitz. 1990. Uptake of host plant alkaloids by root parasitic Pedicularis species. Phytochemistry 29(6): 1811-1814.



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Liberation of the Wild Bergamot

Removal of large honeysuckle bushes (Lonicera spp.) often clears the way for a bazillion tiny honeysuckle bushes, but there can also be native plants patiently waiting for more sunlight. This is what we found growing (this year) where we removed several sprawling honeysuckle  (last year) …

Wild Bergamot

Wild bergamot and other native plants, overshadowed by honeysuckle, were still clinging to life.

These vigorous wild bergamot plants (Monarda fistulosa) are hopefully an indication of what lies ahead if we expand our project and dive into the tangled mess of honeysuckle, other woody plants, and crown vetch (Coronilla varia) growing west of the house. We’ve been nibbling at it, but would like to step up our efforts before it is too late for other native plants growing there .

(Removal of other honeysuckle did not provide such uplifting results.)

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• firm or obstinate continuance in a course of action in spite of difficulty or opposition

• the continued or prolonged existence of something

ORIGIN mid 16th cent.: from French persistance, from the verb persister; influenced in spelling by Latin persistent- ‘continuing steadfastly.’

— New Oxford American Dictionary

We didn’t fully grasp the nature of the path we were about to embark upon when we asked Michael Anderson to burn our prairie remnant and about two acres of surrounding grassland ten years ago. The process appeared simple enough: restore fire to the land so native plants might flourish. I knew very little about native plants and ecology when we started. Actually, I didn’t think much about native plants, especially prairie plants, before Blue Mounds Area Project ecologist Bob Wernerehl told us about the shortgrass prairie remnant growing near our new house. And I certainly didn’t think much about exotic plants and their dreadfully wicked ways. But I was about to learn a lot.

There were the Years of the Thistle, when we invested dozens of hours trying to eradicate solid patches of thistle (Carduus spp. and Cirsium spp.) that firmly stood their ground. We used string trimmers, a lawn mower, a machete, loppers, and, finally, a propane torch to evict them. I seriously wondered whether it was worth the effort. Family and friends had to be called in as reinforcements to work quickly enough to prevent more seed from falling on the ground.

There were the Years of the Sweet Clover, when we invested dozens of hours trying to eradicate solid patches of sweet clover (Melilotus alba) that were advancing toward the relatively pristine prairie remnant forming the core of our project. Year after year, we tried to pull it before it dropped more seed and finally had to ask Errol Jung to mow it down to buy us a little more time. Ideally, a person burns the area two springs in a row to largely eradicate sweet clover, but the weather never cooperated and the bare ground under the thistle and sweet clover interfered with the spread of fire. Again, I wondered whether it was worth the effort.

Then there were the Years of the Wild Parsnip, when we invested dozens of hours pulling and cutting wild parsnip (Pastinaca sativa), preferably late in the day to protect ourselves from the phototoxic sap. I started by pulling the plants a day or so after it rained—or cutting their roots just below the soil surface—and hauling them to the compost pile to avoid dropping viable seed on the ground, but Merel Black offered some sound advice for accelerating the process: cut or mow the plants just before the seeds harden and leave them lay where they fall … the seed aren’t viable and you’ll see far less wild parsnip next year. It really works!

Then there was the Year of Success. Yes, success! Persistence—“continuing steadfastly”—does yield results …

Pale Purple Coneflower

No thistle, sweet clover, or wild parsnip!

Most gardeners know populations of weeds decline if a person breaks the cycle of seed production by annuals and biennials, but it is more than a bit hard to believe when someone is trying to deplete a seed bank that has accumulated for years and might lie dormant for a decade. And when those owning the land around you don’t appear concerned about aggressive exotic plants, it seems futile.

This year, however, we had to dedicate only a few hours to pulling thistle, pulling sweet clover, and cutting wild parsnip. We dedicated just a few hours to surveying two acres of grassland, scanning for aggressive exotic plants, and swiftly removing them. Sure, there are still weeds, there are still plants that don’t belong there. We haven’t burned the area for several years and woody plants—e.g., honeysuckle (Lonicera spp.) and box elder (Acer negundo)—are moving in. I’ve also noticed a few teasel (Discus fullonum). But this is all manageable and we now have some time for expanding our project.

Of course, there’s more to preserving a prairie remnant than controlling aggressive exotic plants. What about enriching the area? What about biodiversity? Well, that’s the other half of the success story. While we were busy tackling thistle, sweet clover, wild parsnip, honeysuckle, and a few other species, we were also collecting and scattering seeds of native plants. As I walked back and forth on my search and destroy mission over the past few weeks, I saw tiny leadplant (Amorpha canescens) where I didn’t expect them and previously absent Illinois tick-trefoil (Desmodium illinoense) scattered throughout the two acres. There’s purple prairie clover (Dalea purpurea) blooming everywhere, far beyond the remnant where we first found it. pale purple coneflower (Echinacea pallida) is expanding its range beyond the small corner where we put just a few plants years ago. Prairie dock (Silphium terebinthinaceum) are reliably sending up flower buds where I previously spent a cool damp November afternoon poking seed into the earth. Butterfly weed (Asclepius tuberosa) is very scarce, but finally establishing a roothold. And clumps of prairie dropseed (Sporobolus heteropolis), little bluestem (Schizachyrium scoparium), big bluestem (Andropogon gerardii), and Indian grass (Sorghastrum nutans) are displacing Eurasian grasses.

The continuous steadfast removal of aggressive exotic plants before they produced more seed yielded results. Learning from others and applying their advice yielded results. Regular collection and scattering of seeds of native plants — though one might not notice until several years later—yielded results. I no longer have to wonder whether it is worth the effort.

This is important … persistence and no longer wondering whether we’ll actually accomplish our goal, for there’s another area containing native plants we’d like to liberate. There’s leadplant, thimbleweed (not sure which one), wild bergamot (Monarda fistulosa), various asters, prairie alumroot (Heuchera richardsonii), and others. It too covers about two acres. The honeysuckle are running rampant, but we’ve managed to reduce the population of thistle and sweet clover. And the wild parsnip is retreating. Errol Jung mowed the infested area last week, which should substantially reduce seed production. BUT … there’s also crown vetch (Coronilla varia), an extremely aggressive exotic plant, extending its tendrils into every nook and cranny. This is a tricky one, as the most effective herbicide for destroying this perennial happens to kill the native leadplant and members of the aster family. I just have to remind myself: persistence will yield results.

And the ultimate result—through our combined work—is persistence of our natural biodiversity, which makes it more than worth the effort.

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