How to Identify Puncture Vine (a.k.a. the Goathead Monster)

This post originally appeared on Idaho Botanical Garden’s blog. With the first annual Boise Goathead Fest fast approaching, the purpose of this post is to help people in the Treasure Valley identify goatheads so that they can collect them for drink tokens to use at the event. I’m reposting it here in hopes that people around the globe who are tormented by goatheads might benefit from it. All photos in this post were taken by Anna Lindquist.


If you have spent much time on a bicycle in Boise, chances are you have been the victim of a goathead-induced flat tire. You probably even got a good look at the spiky nutlet as you went to remove it from your tire. But where did the culprit come from? No doubt, it came from a plant. But which one?

This is particularly useful to know right now because the first annual Boise Goathead Fest is coming up, and if you manage to fill a garbage bag full of these noxious weeds before the end of July, you will earn yourself a drink token. Fortunately, this plant is fairly easy to identify; however, there are a few look-a-likes, so it is important to familiarize yourself with the plant in question so you can be sure you are pulling the right one.

puncture vine (Tribulus terrestris)

Puncture vine, also known as goathead or Tribulus terrestris, is a warm season annual that is native to the Mediterranean region of southern Europe. It was introduced to North America unintentionally by early European settlers when the plant’s blasted burs snuck their way across the ocean in sheep wool. Since then, puncture vine has spread across the continent prolifically thanks to the hitchhiking prowess of its seeds.

Behold, the infamous Goathead Monster.

Puncture vine has a prostrate habit, meaning that its branches lie flat on the ground, spreading outward from a central location. It grows upward only when it is being shaded or crowded out. Its leaves are divided into several tiny leaflets, and its flowers are small and bright yellow with five petals. It is an otherwise pretty plant were it not for the threatening, jagged fruits that follow the flowers. As these fruits dry, they dislodge from the plant, split into five pieces, and lay in wait to puncture your tire, work their way into the bottom of your shoe or the foot of an animal, or latch onto some errant fur.

puncture vine (Tribulus terrestris)

Depending on the conditions, puncture vine either remains fairly small or spreads as much as six feet wide. Fruits start forming shortly after flowering, and seeds ripen soon after that, so if the plant isn’t removed quickly – nutlets and all – future populations are guaranteed. Luckily the plants are fairly easy to remove. Unless the ground is particularly compact, they pull up easily, and if they break off at the root, they generally don’t sprout back.

Virtually any plant that has a prostrate growth habit and is actively growing in the summer could, at first glance, be mistaken for puncture vine. Closer inspection will help confirm the plant’s true identity. Two plants that might confuse you are purslane and spotted spurge. Both of these species can be found growing in full sun in disturbed or neglected sites in close company with puncture vine.

Purslane has tiny, yellow, five-petaled flowers similar to puncture vine; however, its leaves are glossy and succulent-like and its stems and leaves often have a red to purple hue to them. Purslane seeds are miniscule, and while the plant can be a nuisance in a garden bed, it poses no threat to bicycles or wildlife.

purslane (Portulaca oleracea)

Spotted spurge, also known as prostrate spurge, can be quickly distinguished by the milky sap that oozes from its broken stems. Its leaves are generally reddish purple on the undersides with a purple spot on top. Its flowers are minute and its seeds even smaller. Because its sap contains latex and other chemicals, it can irritate the skin and poison creatures that dare eat it.

spotted spurge (Euphorbia maculata)

Both of these plants are introduced, weedy species, so even if they won’t count towards your drink token, it still doesn’t hurt to pull them. Puncture vine, however, is included on Idaho’s noxious weed list, which means it is particularly problematic. So take this opportunity to pull as many as you can, and hopefully we can put a sizeable dent in the population of a plant that has tormented Boise bicyclists for far too long.

See Also: Plant vs. Bike


Idaho’s Native Milkweeds

Concern for monarch butterflies has resulted in increasing interest in milkweeds. Understandably so, as they are the host plants and food source for the larval stage of these migrating butterflies. But milkweeds are an impressive group of plants in their own right, and their ecological role extends far beyond a single charismatic insect. Work to save the monarch butterfly, which requires the expansion of milkweed populations, will in turn provide habitat for countless other organisms. A patch of milkweed teems with life, and the pursuit of a single caterpillar helps us discover and explore that.

Asclepias – also known as the milkweeds – is a genus consisting of around 140 species, 72 of which are native to the United States and Canada. Alaska and Hawaii are the only states in the United States that don’t have a native species of milkweed. The ranges of some species native to the United States extend down into Mexico where there are numerous other milkweed species. Central America and South America are also home to many distinct milkweed species.

The habitats milkweeds occupy are about as diverse as the genus itself – from wetlands to prairies, from deserts to forests, and practically anywhere in between. Some species occupy disturbed and/or neglected sites like roadsides, agricultural fields, and vacant lots. For this reason they are frequently viewed as a weed; however, such populations are easily managed, and with such an important ecological role to play, they don’t deserve to be vilified in this way.

Milkweed species are not distributed across the United States evenly. Texas and Arizona are home to the highest diversity with 37 and 29 species respectively. Idaho, my home state, is on the low end with six native species, most of which are relatively rare. The most common species found in Idaho is Asclepias speciosa commonly known as showy milkweed.

showy milkweed (Asclepias speciosa)

Showy milkweed is distributed from central U.S. westward and can be found in all western states. It occurs throughout Idaho and is easily the best place to look for monarch caterpillars. Side note: the monarch butterfly is Idaho’s state insect, thanks in part to the abundance of showy milkweed. This species is frequently found growing in large colonies due to its ability to reproduce vegetatively via adventitious shoots produced on lateral roots or underground stems. Only a handful of milkweed species reproduce this way. Showy milkweed reaches up to five feet tall and has large ovate, gray-green leaves. Like all milkweed species except one (Asclepias tuberosa), its stems and leaves contain milky, latex sap. In early summer, the stems are topped with large umbrella-shaped inflorescences composed of pale pink to pink-purple flowers.

The flowers of milkweed deserve a close examination. Right away you will notice unique features not seen on most other flowers. The petals of milkweed flowers bend backwards, allowing easy access to the flower’s sex parts if it wasn’t for a series of hoods and horns protecting them. Collectively, these hoods and horns are called the corona, which houses glands that produce abundant nectar and has a series of slits where the anthers are exposed. The pollen grains of milkweed are contained in waxy sacs called pollinia. Two pollinia are connected together by a corpusculum giving this structure a wishbone appearance. An insect visiting the flower for nectar slips its leg into the slit, and the pollen sacs become attached with the help of the corpusculum. When the insect leaves, the pollen sacs follow where they can be inadvertently deposited on the stigmas of another flower.

Milkweed flowers are not self-fertile, so they require assistance by insects to sexually reproduce. They are not picky about who does it either, and their profuse nectar draws in all kinds of insects including bees, butterflies, moths, beetles, wasps, and ants. Certain insects – like bumble bees and other large bees – are more efficient pollinators than others. Once pollinated, seeds are formed inside a pod-like fruit called a follicle. The follicles of showy milkweed can be around 5 inches long and house dozens to hundreds of seeds. When the follicle matures, it splits open to release the seeds, which are small, brown, papery disks with a tuft of soft, white, silky hair attached. The seeds of showy milkweed go airborne in late summer.

follicles forming on showy milkweed (Asclepias speciosa)

Whorled or narrowleaf milkweed (Asclepias fascicularis) is widespread in western Idaho and neighboring states. It is adapted to dry locations, but can be found in a variety of habitats. Like showy milkweed, it spreads rhizomatously as well as by seed. Its a whispy plant that can get as tall as four feet. It has long, narrow leaves and produces tight clusters of greenish-white to pink-purple flowers. Its seed pods are long and slender and its seeds are about 1/4 inch long.

flowers of Mexican whorled milkweed (Asclepias fascicularis)

seeds escaping from the follicle of Mexican whorled milkweed (Asclepias fascicularis)

Swamp or rose milkweed (Asclepias incarnata) is more common east of Idaho, but occurs occasionally in southwestern Idaho. As its common names suggests, it prefers moist soils and is found in wetlands, wet meadows, and along streambanks. It can spread rhizomatously, but generally doesn’t spread very far. It reaches up to four feet tall, has deep green, lance-shaped leaves, and produces attractive, fragrant, pink to mauve, dome-shaped inflorescenses at the tops of its stems. Its seed pods are narrow and around 3 inches long.

swamp milkweed (Asclepias incarnata)

Asclepias cryptoceras, or pallid milkweed, is a low-growing, drought-adapted, diminutive species that occurs in southwestern Idaho. It can be found in the Owyhee mountain range as well as in the Boise Foothills. It has round or oval-shaped leaves and produces flowers on a short stalk. The flowers have white or cream-colored petals and pink-purple hoods.

pallid milkweed (Asclepias cryptoceras)

The two remaining species are fairly rare in Idaho. Antelope horns (Asclepias asperula) is found in Franklin County located in southeastern Idaho. It grows up to two feet tall with an upright or sprawling habit and produces clusters of white to green-yellow flowers with maroon highlights. Horsetail milkweed (Asclepias subverticillata) occurs in at least two counties in central to southeastern Idaho and is similar in appearance to A. fascicularis. Its white flowers help to distinguish between the two. Additional common names for this plant include western whorled milkweed and poison milkweed.

Eating Weeds: Pineapple Weed

When I wrote about pineapple weed (Matricaria discoidea) last year during the Summer of Weeds, I knew that it was edible but I didn’t bother trying it. Pineapple weed is one of my favorite native weeds (yes, it happens to be a native of northwestern North America). I enjoy its sweet fragrance, its frilly leaves, its “petal”-less flowers, and its diminutive size. I also appreciate its tough nature. Now that I have tried pineapple weed tea, I have another thing to add to this list of pros.

pineapple weed (Matricaria discoidea)

One thing about pineapple weed that always impresses me is its ability to grow in the most compacted soils. It actually seems to prefer them. It is consistently found in abundance in highly trafficked areas, like driveways, parking lots, and pathways, seemingly unfazed by regular trampling. Referring to pineapple weed in one of his books about wildflowers, botanist John Hutchinson wrote, “the more it is trodden on the better it seems to thrive.” This is not something you can say about too many other plants.

Both the leaves and flowers of pineapple weed are edible. The flowers seem to be the more common of the two to consume, generally in tea form. In his book Wild Edible and Useful Plants of Idaho, Ray Vizgirdas writes, “A delicious tea can be made from the dried flowers of the plant. The leaves are edible, but bitter. The medicinal uses of pineapple weed are identical to that of chamomile (Anthemis). Used as a tea it is a carminative, antispasmodic, and mild sedative.” In Wild Urban Plants of the Northeast, Peter Del Tredici writes, “A tea made from the leaves has been used in traditional medicine for stomachaches and colds.”

I harvested my pineapple weed at the end of a dirt parking lot and in an adjacent driveway/pathway. I noted how the pineapple weed’s presence waned as I reached the edges of the parking lot and pathway where, presumably, the ground was less compact. Maybe it has more to compete with there – other weeds – and so it shows up less, or maybe its roots simply “prefer” compact soils. Perhaps a little of both. Once I got my harvest home, I rinsed it off and left it to dry. Later, I snipped off the flower heads and made a tea.

I probably used more water than I needed to, so it was a bit diluted, but it was still delicious. It smelled and tasted a lot like chamomile. Sierra agreed. With a little honey added, it was especially nice. Sierra agreed again. The flowers of pineapple weed can be used fresh or dried. They can also be mixed with other ingredients to make a more interesting tea, like the recipe found here.

If you are hesitant to take the leap into eating weeds, a tea may be the simplest thing you can try. Pineapple weed tea is a great way to ease yourself into it. Apart from maybe having to harvest it from strange places, it probably isn’t much different from other teas you have tried, and, from my experience, it’s delightful.

When Urban Pollinator Gardens Meet Native Plant Communities

Public concern about the state of bees and other pollinating insects has led to increased interest in pollinator gardens. Planting a pollinator garden is often promoted as an excellent way for the average person to help protect pollinators. And it is! However, as with anything in life, there can be downsides.

In many urban areas, populations of native plants remain on undeveloped or abandoned land, in parks or reserves, or simply as part of the developed landscape. Urban areas may also share borders with natural areas, the edges of which are particularly prone to invasions by non-native plants. Due to human activity and habitat fragmentation, many native plant populations are now threatened. Urban areas are home to the last remaining populations of some of these plants.

Concern for native plant populations in and around urban areas prompted researchers at University of Pittsburgh to review some of the impacts that urban pollinator gardens may have and to develop a “roadmap for research” going forward. Their report was published earlier this year in New Phytologist.

Planting a wildflower seed mix is a simple way to establish a pollinator garden, and such mixes are sold commercially for this purpose. Governmental and non-governmental organizations also issue recommendations for wildflower, pollinator, or meadow seed mixes. With this in mind, the researchers selected 30 seed mixes “targeted for urban settings in the northeastern or mid-Atlantic USA” to determine what species are being recommended for or commonly planted in pollinator gardens in this region. They also developed a “species impact index” to assess “the likelihood a species would impact remnant wild urban plant populations.”

A total of 230 species were represented in the 30 seed mixes. The researchers selected the 45 most common species for evaluation. Most of these species (75%) have generalized pollination systems, suggesting that there is potential for sharing pollinators with remnant native plants. Two-thirds of the species had native ranges that overlapped with the targeted region; however, the remaining one-third originated from Europe or western North America. The native species all had “generalized pollination systems, strong dispersal and colonization ability, and broad environmental tolerances,” all traits that could have “high impacts” either directly or indirectly on remnant native plants. Other species were found to have either high dispersal ability but low chance of survival or low dispersal ability but high chance of survival.

This led the researchers to conclude that “the majority of planted wildflower species have a high potential to interact with native species via pollinators but also have the ability to disperse and survive outside of the garden.” Sharing pollinators is especially likely due to super-generalists like the honeybee, which “utilizes flowers from many habitat types.” Considering this, the researchers outlined “four pollinator-mediated interactions that can affect remnant native plants and their communities,” including how these interactions can be exacerbated when wildflower species escape gardens and invade remnant plant communities.

photo credit: wikimedia commons

The first interaction involves the quantity of pollinator visits. The concern is that native plants may be “outcompeted for pollinators” due to the “dense, high-resource displays” of pollinator gardens. Whether pollinator visits will increase or decrease depends on many things, including the location of the gardens and their proximity to native plant communities. Pollinator sharing between the two has been observed; however, “the consequences of this for effective pollination of natives are not yet understood.”

The second interaction involves the quality of pollinator visits. Because pollinators are shared between native plant communities and pollinator gardens, there is a risk that the pollen from one species will be transferred to another species. High quantities of this “heterospecific pollen” can result in reduced seed production. “Low-quality pollination in terms of heterospecific pollen from wildflower plantings may be especially detrimental for wild remnant species.”

The third interaction involves gene flow between pollinator gardens and native plant communities. Pollen that is transferred from closely related species (or even individuals of the same species but from a different location) can have undesired consequences. In some cases, it can increase genetic variation and help address problems associated with inbreeding depression. In other cases, it can introduce traits that are detrimental to native plant populations, particularly traits that disrupt adaptations that are beneficial to surviving in urban environments, like seed dispersal and flowering time. Whether gene flow between the two groups will be positive or negative is difficult to predict, and “the likelihood of genetic extinction versus genetic rescue will depend on remnant population size, genetic diversity, and degree of urban adaptation relative to the planted wildflowers.”

The fourth interaction involves pathogen transmission via shared pollinators. “Both bacterial and viral pathogens can be transmitted via pollen, and bacterial pathogens can be passed from one pollinator to another.” In this way, pollinators can act as “hubs for pathogen exchange,” which is especially concerning when the diseases being transmitted are ones for which the native plants have not adapted defenses.

photo credit: wikimedia commons

All of these interactions become more direct once wildflowers escape gardens and establish themselves among the native plants. And because the species in wildflower seed mixes are selected for their tolerance of urban conditions, “they may be particularly strong competitors with wild remnant populations,” outcompeting them for space and resources. On the other hand, the authors note that, depending on the species, they may also “provide biotic resistance to more noxious invaders.”

All of these interactions require further investigation. In their conclusion, the authors affirm, “While there is a clear potential for positive effects of urban wildflower plantings on remnant plant biodiversity, there is also a strong likelihood for unintended consequences.” They then suggest future research topics that will help us answer many of these questions. In the meantime, pollinator gardens should not be discouraged, but the plants (and their origins) should be carefully considered. One place to start is with wildflower seed mixes, which can be ‘fine-tuned’ so that they benefit our urban pollinators as well as our remnant native plants. Read more about plant selection for pollinators here.

Managing Spontaneous Urban Plants for Improved Aesthetics

As discussed last week, our wild, urban flora is a cosmopolitan mixture of plants that were either native to the area before it was developed, introduced from all corners of the world on purpose or by accident, or brought in by migrating wildlife. These are plants capable of establishing and sustaining themselves outside of human cultivation and management, and are found in abundance beyond the borders of our tidy gardens and manicured landscapes. They vegetate sectors of our city that have been abandoned, overlooked, or routinely neglected. Given enough time – and prolonged lack of intervention – such vegetation will proceed along the process of ecological succession in the same way that plant communities in natural areas do. And just like other plant communities within their respective ecosystems, these wild, urban plant communities provide a suite of ecological services vital to the health of our urban ecosystems.

Peter Del Tredici writes in Wild Urban Plants of the Northeast, “landscapes that include spontaneous vegetation fit the technical definition of sustainable in the sense that they are adapted to the site, require minimal maintenance, and are ecologically functional.” In an interview with Scenario Journal, Del Tredici goes on to define sustainability as “the value of the services provided by the ecosystem divided by the cost required to maintain that ecosystem.” Spontaneous urban landscapes offer “substantial ecological services at relatively low cost, or in some cases no cost,” and thus, by Del Tredici’s definition, they are “highly sustainable.”

There is one unfortunate downside – “weedy” landscapes like this are, by popular opinion, thoroughly unattractive and a sign of urban decay. This belief is held in spite of the fact that many of the plants found therein would be cherished or admired in other settings. Among deteriorating infrastructure, litter, and less attractive plants, some of our favorite plants are rendered guilty by association.

Despite their ecological benefits, abandoned areas vegetated with wild, urban plants are not favored by the public. So, to appease our aesthetic standards, sites like this can be enhanced through minimal intervention to be more attractive while retaining their ecological functions. In a paper published in a 2006 issue of Journal of Landscape Architecture, Norbert Kühn asserts that “to use spontaneous vegetation for ornamental purposes, a kind of enhancement or design work is necessary.” Species can be added and removed, and simple, infrequent maintenance measures can be implemented. Examples include extending the flowering season with spring flowering bulbs and mowing the area once or twice annually to maintain and improve the composition of the stand.

Wild bergamot (Monarda fistulosa) – one of the plants that Norbert Kühn included in his study as a candidate for improving the aesthetics of spontaneous, urban plant communities.

Favoring attractive weeds over less attractive ones and using minimal maintenance to improve aesthetics and function are the principles behind Del Tredici’s “cosmopolitan urban meadow.” In his book, he lists some criteria for plants that would be suitable for “this novel landscape form,” including: erosion control (long-lived; vegetatively spreading), stress tolerance (full sun; drought; compacted and polluted soil), aesthetic value (ornamental characteristics; not “weedy” looking), wildlife friendly (attractive to pollinators; edible seeds), and commercially available.

In an article in Harvard Design Magazine, Del Tredici and Michael Luegering describe the cosmopolitan urban meadow as “a stable assemblage of stress-tolerant, low-maintenance herbaceous perennial plants that are preadapted to harsh urban conditions and that will provide an attractive vegetation cover on vacant land.” Whether it is a “long-term landscape feature” or a placeholder until future development, it will have “the capacity to increase the aesthetic and ecological value of vacant land without the investment of large sums of money typically required for the installation and maintenance of traditional managed landscapes.”

Abandoned or undeveloped, urban lots like this one are ideal sites for “cosmopolitan urban meadows.”

In an urban context, some plant species are particularly noxious and may need to be removed from urban meadows, such as ragweed (Ambrosia spp.) for its allergens and poison ivy (Toxicodendron radicans) for its Urushiol-induced contact dermatitis. Species with a history of being invasive should also be avoided and contained, particularly in sites that are adjacent to or within a short distance from natural areas. Despite this and other minor concerns, spontaneous vegetation has great potential. In Kühn’s words it is “authentic” and a “reminder of the history of the site,” it is part of “the natural dynamic” with potential to bring us “closer to nature,” and finally, “it can be maintained for a long time [with] less care and low costs.”

Finding beauty in these urban, wild landscapes might even cause a shift in what we find appropriate for cultivated landscapes. In her book, Grow Curious, Gayla Trail reminds us that, despite all of our efforts, wildness persists even in our most earnest attempts to subdue it. Perhaps we should embrace it:

‘Wild’ and ‘cultivated’ are social constructs that we place in opposition to each other, when in reality there is a knotty labyrinth between them. We subjugate our cities and our gardens with chemicals and artifice because we are unable to see that wild and cultivated can be entwined, can be all at once tended, lyrical, surprising, domesticated, irrational, functional, and free.


See Also: Arnold Arboretum’s Cosmopolitan Meadow at Weld Hill

When Sunflowers Follow the Sun

Tropisms are widely studied biological phenomena that involve the growth of an organism in response to environmental stimuli. Phototropism is the growth and development of plants in response to light. Heliotropism, a specific form of phototropism, describes growth in response to the sun. Discussions of heliotropism frequently include sunflowers and their ability to “track the sun.” This conjures up images of a field of sunflowers in full bloom following the sun across the sky. However cool this might sound, it simply doesn’t happen. Young sunflowers, before they bloom, track the sun. At maturity and in bloom, the plants hold still.

What is happening in these plants is still pretty cool though, and a report published in an August 2016 issue of Science sheds some light on the heliotropic movements of young sunflowers. They begin the morning facing east. As the sun progresses across the sky, the plants follow, ending the evening facing west. Over night, they reorient themselves to face east again. As they reach maturity, this movement slows, and most of the flowers bloom facing east. Over a series of experiments, researchers were able to determine the cellular and genetic mechanisms involved in this spectacular instance of solar tracking.

Helianthus annuus (common sunflower) is a native of North America, sharing this distinction with dozens of other members of this recognizable genus. It is commonly cultivated for its edible seeds (and the oil produced from them) as well as for its ornamental value. It is a highly variable species and hybridizes readily. Wild populations often cross with cultivated ones, and in many instances the common sunflower is considered a pesky weed. Whether crop, wildflower, or weed, its phototropic movements are easy to detect, making it an excellent subject of study.

Researchers began by tying plants to stakes so that they couldn’t move. Other plants were grown in pots and turned to face west in the morning. The growth of these plants was significantly stunted compared to plants that were not manipulated in these ways, suggesting that solar tracking promotes growth.

The researchers wondered if a circadian system was involved in the movements, and so they took sunflowers that had been growing in pots in a field and placed them indoors beneath a fixed overhead light source. For several days, the plants continued their east to west and back again movements. Over time, the movements became less detectable. This and other experiments led the researchers to conclude that a “circadian clock guides solar tracking in sunflowers.”

Another series of experiments helped the researchers determine what was happening at a cellular level that was causing the eastern side of the stem to grow during the day and the western side to grow during the night. Gene expression and growth hormone levels differed on either side of the stem depending on what time of day it was. In an online article published by University of California Berkeley, Andy Fell summarizes the findings: “[T]here appear to be two growth mechanisms at work in the sunflower stem. The first sets a basic rate of growth for the plant, based on available light. The second, controlled by the circadian clock and influenced by the direction of light, causes the stem to grow more on one side than another, and therefore sway east to west during the day.”

The researchers observed that as the plants reach maturity, they move towards the west less and less. This results in most of the flowers opening in an eastward facing direction. This led them to ask if this behavior offers any sort of ecological advantage. Because flowers are warmer when they are facing the sun, they wondered if they might see an increase in pollinator visits during morning hours on flowers facing east versus those facing west. Indeed, they did: “pollinators visited east-facing heads fivefold more often than west-facing heads.” When west-facing flowers where warmed with a heater in the morning, they received more pollinator visits than west-facing flowers that were not artificially warmed, “albeit [still] fewer than east-facing flowers.” However, increased pollinator visits may be only part of the story, so further investigations are necessary.


I’m writing a book about weeds, and you can help. For more information, check out my Weeds Poll.

Summer of Weeds: Willowherbs and Fireweed

Last week we discussed a plant that was introduced as an ornamental and has become a widespread weed. This week we discuss some native plants that have become weedy in places dominated by humans. Similar to pineapple weed, species in the genus Epilobium have moved from natural areas into agricultural fields, garden beds, and other sites that experience regular human disturbance. Some species in this genus have been deliberately introduced for their ornamental value, but others have come in on their own. In all cases the story is similar, humans make room and opportunistic plants take advantage of the space.

Epilobium species number in the dozens and are distributed across the globe. North America is rich with them. They are commonly known as willowherbs and are members of the evening primrose family (Onagraceae). They are herbaceous flowering plants with either annual or perennial life cycles and are commonly found in recently disturbed sites, making them early successional or pioneer species. Many are adapted to wet soils and are common in wetlands and along streambanks; others are adapted to dry, open sites. Hybridization occurs frequently among species in the Epilobium genus, and individual species can be highly variable, which may make identifying them difficult.

northern willowherb (Epilobium ciliatum)

At least two North American species are commonly weedy: E. ciliatum (northern willowherb) and E. brachycarpum (panicled willowherb). Regarding these two species, the IPM website of University of California states: “Willowherbs are native broadleaf plants but usually require a disturbance to establish. Although considered desirable members of natural habitats, they can be weedy in managed urban and agricultural sites.” The field guide, Weeds of the West, refers to E. brachycarpum as a “highly variable species found mostly on non-cultivated sites, and especially on dry soils and open areas.” E. ciliatum is notorious for being a troublesome weed in greenhouses and nurseries, as discussed on this Oregon State University page.

E. ciliatum is a perennial that reproduces via both rhizomes and seeds. It reaches up to five feet tall and has oppositely arranged, lance-shaped leaves with toothed margins that are often directly attached to the stems. Its flowers are tiny – around a quarter of an inch wide – and white, pink, or purple with four petals that are notched at the tip. They sit atop a skinny stalk that is a few centimeters long, which later becomes the fruit. When dry, the fruit (or capsule) splits open at the top to reveal several tiny seeds with tufts of fine hairs.

northern willowherb (Epilobium ciliatum)

E. brachycarpum is an annual that reaches up to three feet tall and is highly branched. Its leaves are short and narrow and mostly alternately arranged. Its flowers and seed pods are similar to E. ciliatum. At first glance it can appear as one of many weeds in the mustard family; however, the tuft of hairs on its seeds distinguishes it as a willowherb.

Seeds and seed pods of panicled willowherb (Epilobium brachycarpum)

Weeds of North America by Richard Dickinson and France Royer describes one weedy species of willowherb that was introduced to North America from Europe – E. hirsutum. It is commonly referred to as great hairy willowherb, but some of its colloquial names are worth mentioning: fiddle grass, codlins and cream, apple-pie, cherry-pie, blood vine, and purple rocket. Introduced as an ornamental in the mid 1800’s, it is a semiaquatic perennial that can reach as tall as eight feet. It has small, rose-purple flowers and is frequently found growing in wetlands along with purple loosestrife (Lythrum salicaria).

Chamerion angustifolium – which is synonymously known as Epilobium angustifolium and commonly called fireweed – is distributed throughout temperate regions of the Northern Hemisphere. It is a rhizomatously spreading perennial that grows to nine feet tall; has lance-shaped, stalkless leaves; and spikes of eye-catching, rose to purple flowers. It is a true pioneer species, found in disturbed sites like clear-cuts, abandoned agricultural fields, avalanche scars, and along roadsides. It gets its common name for its reputation of being one of the first plants to appear after a fire, as John Eastman describes in The Book of Field and Roadside: “A spring fire may result in a profusion of growth as soon as 3 months afterward, testifying to fireweed’s ample seed bank in many wilderness areas.” Eastman goes on to write, “fireweed’s flush of abundance following fire may rapidly diminish after only a year or two of postburn plant growth.” This “flush of abundance” is what gives it its weedy reputation in gardens. With that in mind, it is otherwise a welcome guest thanks to its beauty and its benefit to pollinators.

fireweed (Chamerion angustifolium)

Additional Resources:

Quote of the Week:

From the book Food Not Lawns by H.C Flores

Sometimes [weeding] feels like playing God – deciding who lives and who dies is no small matter – and sometimes it feels like war. … Take a moment to ponder the relationship of these plants to other living things around, now and in the future. Your weeds provide forage and habitat for insects, birds, and animals, as well as shelter for the seedlings of other plants. They cover the bare soil and bring moisture and soil life closer to the surface, where they can do their good work. Weeds should be respected for their tenacity, persistence, and versatility and looked upon more as volunteers than as invaders.