invasive species

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Garden Plants Gone Wild: The Periwinkles

In a garden setting, a successful groundcover is a plant that is durable and adaptable, spreads readily, and fills in space thouroughly. The point of planting a groundcover is to cover exposed soil and create a sort of living mulch. In fact, groundcovers provide similar benefits to mulch. They prevent erosion, help retain soil moisture, and prevent weeds. It should come as no surprise then, that a plant that fulfills all of these requirements has the potential to become a weed, especially if given the opportunity to escape and establish itself outside of its intended location.

This isn’t a hypothetical. This exact scenario has played out numerous times. A good example of this are the periwinkles: Vinca major and Vinca minor. Both have been popular garden plants for centuries. Their introduction to U.S. gardens came as early as the 1700’s. Today, both species (including cultivars of each) can be found for sale in nurseries throughout the country, even while escaped periwinkles proceed to spread across natural areas and uncultivated spaces. Even in gardens where periwinkles have been intentionally planted, they can be deemed no longer welcome due to their aggressive nature. Eliminating them, however, is a formidable task.

greater periwinkle (Vinca major)

Periwinkles are relatively easy to identify, yet telling the two apart can sometimes pose a challenge. Knowing what to look for can make this a fairly simple task. Vinca major (greater periwinkle) is the larger of the two. Its stems are tough and sprawl up to 5 feet long, rooting adventitiously when in contact with the ground. Vegetative spread also occurs via stolons and rhizomes, modified stems that spread horizontally both above and below ground and whose main purpose is to produce new roots along their length. This extensive rooting creates dense mats of stems and foliage, precisely what you’d want from an effective groundcover. Leaves are arranged oppositely and are semi-evergreen with fine hairs along their margins. They are thick, glossy, simple, dark green, and ovate to ovate-lanceolate in shape. They have a relatively long petiole, and some leaves can even appear heart-shaped.

The flowers of V. major are blue to purple and fused at the base to form a tube, separating into five distinct lobes and creating a shape similar to a pinwheel. They are borne on a long stalk in the axils of leaves and measure about two inches wide. Their sepals are long, slender, pointed, and lined with bristly hairs. Fruits rarely form, but when they do, they are narrow follicles.

comparing the petals and sepals of Vinca major (left) and Vinca minor (right)

Vinca minor (lesser periwinkle) is a slightly smaller plant with a similar habit, spreading vegetatively in all the same ways as V. major. Stems are slender and smooth and leaves are evergreen. Compared to V. major, the leaves of V. minor are smaller, narrower, and have hairless margins and short petioles, otherwise they are very similar. Same goes for the flowers, which look identical on both species, except that those of V. minor are slightly smaller (about one inch wide) and borne on shorter stalks. Sepals are shorter, broader, more rounded at the tips, and lack the bristly hairs of V. major.

Because periwinkles only rarely produce seed, their main method of getting around is vegetatively. Fragments of roots or rhizomes hide in soil and are moved from one location to another inadvertently. Periwinkles are often used in hanging baskets and containers, and when these things are cast aside at the end of a season, the perennial roots of periwinkles may continue to grow, spreading out beyond the potting mix and into the soil.

Dump soil, yard waste, and improperly disposed of containers are the main ways that periwinkles find their way into natural areas. Both species can be found in the understories and edge habitats of woodlands, as well as along roadsides and pathways, and in vacant lots and old homesites. They can also be found in riparian areas, where waterways can carry fragments of plants to new locations. The Invasive Plant Atlas compiles reports of both V. major and V. minor growing outside of cultivation and tracks them on a map. They also track which states include them in noxious weeds lists or laws.

lesser periwinkle (Vinca minor)

The best way to keep periwinkles from continuing to spread outside of cultivation is to refrain from growing them. If you choose to have them in your yard, dispose of plant parts properly. If you keep them in containers, send those containers to the landfill when you are done with them. If your property is adjacent to natural areas, the risk may be too great and you may want to consider a different groundcover. Depending on where you live, alternatives vary. In the Intermountain West, potential substitutes include wild strawberry (Fragaria virginiana), woodland strawberry (F. vesca), kinnikinnik (Arctostaphylos uva-ursi), and wild ginger (Asarum caudatum). Each of these are low growing, evergreen to semi-evergreen, spreading plants that do well in shade and can handle some degree of drought.

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Horticulture’s Weedy Introductions in a Changing Climate

In case I need a reminder that the horticulture industry has a history of introducing weedy plants to natural areas, I get one each time I bike to work. Riding along the Boise River Greenbelt, a trail that for much of its length is flanked by cultivated landscapes on one side and a highly modified but largely naturalized river bank on the other, I see a mixture of both native and introduced plants. Of the introduced plants, many are horticultural species that have escaped cultivation and established themselves on the bank of the river. There are catalpa and black locust trees brought in from the other side of the country, St. John’s wort and chicory from Eurasia, honeysuckles primarily from Asia, and a few different cherry species and hybrids with varied provenances. And this is just a small sample of what can be found along my three and a half mile bike ride.

St. John’s wort (Hypericum perforatum) on the banks of the Boise River

This is certainly not a new concern. We have been aware of the role that horticulture plays in introducing invasive species for quite some time now. Several years back, while doing a deep dive into the topic of invasive species, I wrote about this issue right here on this very blog. According to a study published in Frontiers in Ecology and the Environment (2021), out of 1285 plant species identified as invasive, 61% are currently sold in nurseries. If that’s not concern enough, an additional factor to consider is climate change. Plants that were less likely to escape cultivation and head for the wild, may take the opportunity to do so in a changing climate. Plus, horticultural plants that are already problems in certain areas could expand their range as climates become more favorable in new locations, especially if these plants continue to be sold in nearby nurseries.

These concerns and more are the topic of a paper published in BioScience (2023). Evelyn M. Beaury, et al. looked at nurseries across the United States and the plants they sell in order to determine where invasive plants are still being sold in regions where they are invasive. Additionally, they looked at plants known to be invasive but that are not currently invasive in the regions they are being sold. Using climate models, they predicted whether or not these plants could become invasive under changing climates.

Plants are being moved around with a lot more ease than they once were, and the sales of problematic plants are increasingly difficult to regulate. For one thing, plants prohibited for sale in one state can be purchased at nurseries in neighboring states and brought back to be planted in regions where those plants are invasive. And while mail order has existed for a long time, online ordering makes the process even simpler; and many online plant vendors are not liscensed nurseries, making them much more difficult to regulate. But even regulation is typically a response to something that has already become a problem, rather than a proactive measure to prevent plants from escaping into natural areas.

Beaury, et al. identified 672 nurseries across the United States, both online and traditional retailers. Each of these nurseries were selling one or more of the 89 plant species that became the focus of their research. These are plant species that are either on federal or state noxious weed lists or that have been identified as invasive by Invasive Plant Atlas. The reach of each nursery was determined by using customer reviews to compute distances that plants might travel after being purchased at nurseries or from online stores. Obviously, not every customer that purchases a plant leaves a review, but this is a good way to get a general idea how far away customers are from nurseries without having access to more detailed records. These geotagged reviews can also be cross-referenced with known distributions of invasive plants. Using climate models and environmental predictor variables, the researchers determined areas of current and potential invasion for each of the 89 plants.

tansy (Tanacetum vulgare) – one of the 89 plant species looked at in the study

The first question was about proximity to current records of plant invasions. Results showed that “49 of the 89 ornamental invasives were sold within 21 kilometers (13 miles) of an observed record of invasion.” When invasive plants are sold and planted near locations where they are already known to be invasive, it gives them the opportunity to add new plants to existing or developing invasions. In ecology, this is known as propagule pressure. When it comes to current and future climate, most species in the study are being sold by nurseries where the climate is either currently favorable for range expansion or may eventually become favorable. Specifically for future climate, 40 of the 89 plants are being sold in regions that are currently suitable for invasion and will continue to be suitable as the climate changes, and 25 of the 89 plants are being sold in regions where the climate is currently unsuitable but will become suitable as temperatures warm.

Particularly for plants being sold in areas that are not yet suitable for invasion, there is time to educate both the nursery industry and the general public and to look for alternatives to these plants. However, as the researchers point out, their analysis “only examined about 10% of the larger pool of U.S. ornamental plants known to be invasive,” and they “sampled only a subset of the nurseries that could be selling invasive species in the United States.” It is highly likely that the results of this study are an underestimation of the problem. Clearly the work of education and finding alternatives to problematic plants is monumental. The hope is that studies like this can help with education and can assist with working out ways to regulate sales of invasive plants.

coltsfoot (Tussilago farfara) – another one of the 89 plant species looked at in the study

Regulating the sale of plants is beyond most of our control, and how much regulation we should be enforcing on nurseries in the first place is a debate we should be having. Outside of those questions, there is a responsibility that we should take as gardeners and as residents of the planet. If we choose to grow plants, it is crucial that we get to know them. We should be taking the time to observe the degree to which they spread and how they are being dispersed. When they do move around our yards, where are they going, and are they able to grow outside of our care? Are they leaving our properties and coming up elsewhere? If we choose to plant non-native species, we should be mindful of how they might affect nearby, wild landscapes if they were to escape our yards and establish themselves in these locations. We should also be aware of where we live in the city. If our gardens are in the middle of a dense urban landscape, perhaps there is less concern that our plants will move beyond the borders of our gardens. But if we garden near natural areas, we should be significantly more selective about the things we plant, and we ought to be more observant as to what those plants are up to.

Nurseries generally sell the plants that gardeners want to buy, which means we can choose not to buy problematic plants and instead demand alternatives to these plants. Seeking out nurseries that sell the types of plants that are better suited for our regions and do not exhibit invasive behaviors can send a message to other growers that they should phase out certain plants and start growing the plants that gardeners are asking for. This may be a simplistic take, and as with most things, it’s complicated. While one of the goals of this research is to help influence regulators, another goal is simply to “[share] information about high-risk ornamental invaders across states and regions, and [work] with horticulture and community members to reduce the escape of ornamental species into natural areas.” This is precisely the area where gardeners can make a difference.

On that note, I will be starting a new series of posts to discuss some of the ornamental species that have gone weedy. By getting to know the plants that find themselves in this predicament, we can be better situated to make informed decisions about what to do about them.

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Weeds of Boise: Neglected Parking Lot Islands at Post Office on 13th Street

Boise’s summers are decidedly hot and dry. Months can pass without any measurable precipitation, meanwhile temperatures regularly peak in the 90’s. In the heat of the summer, multiple days in a row above 100 degrees Fahrenheit is not unheard of. Under these conditions, irrigation is a must if you intend to keep plants alive, particularly plants not adapted to our climate. Skipping out on watering or having something go awry with the irrigation system quickly becomes noticeable as the soil goes bone dry and plants begin to wither away. If this goes on for too long, many plants will not recover, including established trees and shrubs. However, the toughest plants among us, particularly the weeds, will move in to take their place.

You can see an example of this at the United States Postal Service building at 13th Street and Shoreline Lane in Boise, Idaho. The islands in the parking lot are not being watered, which has clearly been the case for quite some time because even the trees and shrubs are dying off. Apart from occasional mowing, very little maintenance is occurring, and our wild urban flora is about all that remains.

parking lot island at the corner of 13 Street and Shoreline Lane

Parking lots are not ideal locations for growing plants. Asphalt and cement dominate – two major contributors to the urban heat island effect – and automobile pollution is concentrated on account of all the cars coming and going on a regular basis. Many parking lots include islands where plants (often poorly maintained), along with other features like signs and lights, are placed. In general, these islands are far too small for trees, but trees are planted nonetheless in a desperate attempt to shade these formidable environments. In locations where snow is common, the snow from parking lots is often piled up on these islands to clear room for cars, while road salts and other ice melts are heavily applied in order to keep people and cars from sliding around. Parking lot plants have to endure all this and more, so it’s no surprise that they usually look pretty rough.

The stresses of added heat, pollution, trampling, and poor care are enough for plants to put up with. Cut off their irrigation supply, and parking lot plants are sure to give up the ghost. A situation like this is an excellent place to familiarize yourself with your wild urban flora. Many weeds seemingly have no problem tolerating these conditions. To demonstrate this, I inventoried the weeds found in neglected parking lot islands at the post office on 13th Street and Shoreline Lane. What follows are a few photos and a list of the weeds I’ve identified so far. Like all posts in the Weeds of Boise series, this list may be updated as I continue to check back in on this location.

spring draba (Draba verna)
shepherd’s purse (Capsella bursa-pastoris)
dandelion (Taraxacum officinale)
black medic (Medicago lupulina)
crabgrass (Digitaria sanguinalis)
annual sow thistle (Sonchus oleraceus)
snag (aka standing dead tree) at post office on 13th Street
  • Anthriscus caucalis (bur chervil)
  • Bromus tectorum (cheatgrass)
  • Capsella bursa-pastoris (shepherd’s purse)
  • Ceratocephala testiculata (bur buttercup)
  • Chondrilla juncea (rush skeletonweed)
  • Claytonia perfoliata (miner’s lettuce)
  • Convolvulus arvensis (field bindweed)
  • Conyza canadensis (horseweed)
  • Digitaria sanguinalis (crabgrass)
  • Draba verna (spring draba)
  • Elymus repens (quackgrass)
  • Epilobium ciliatum (willowherb)
  • Erodium cicutarium (redstem filare)
  • Euphorbia maculata (spotted spurge)
  • Holosteum umbellatum (jagged chickweed)
  • Hordeum jubatum (foxtail barley)
  • Lactuca serriola (prickly lettuce)
  • Lamium amplexicaule (henbit)
  • Malva neglecta (common mallow)
  • Medicago lupulina (black medic)
  • Parthenocissus quinquefolia (Virginia creeper)
  • Poa annua (annual bluegrass)
  • Polygonum aviculare (prostrate knotweed)
  • Portulaca oleracea (purslane)
  • Senecio vulgaris (common groundsel)
  • Sonchus oleraceus (annual sow thistle)
  • Taraxacum officinale (dandelion)
  • Tragopogon dubius (salsify)
  • Tribulus terrestris (puncturevine)
  • Trifolium sp. (clover)

Where there are parking lot islands, there are bound to be weeds whether the islands are being maintained or not. What have you found growing in the parking lot islands in your city? Feel free to share in the comment section below.

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Weeds of Boise: Boise State University Campus, part two

In part one of this two part series, I introduced you to the Boise State University campus, located in the heart of Boise, Idaho. I’ve been spending the past year walking the campus and cataloging the weeds that I find there. Boise has a fairly mild climate compared to the rest of Idaho, so weeds are generally easy to find just about any time of year. What weeds are present depends on what time of year it is. To get a complete picture of the suite of weeds that can be found on a site, it’s important to make observations throughout the year. Weeds can also come and go, with certain species becoming more abundant in some years than others, so making observations over multiple years also helps. This is why I try to update posts that are part of the Weeds of Boise series as I make return visits and encounter additional weed species.

What follows is the second half of the list of weeds I’ve documented so far at Boise State University. I’m including a photograph for each month of the year (July – December), as well as a list of what I’ve encountered up to this point. I’m also including a list of weeds that I didn’t come across but that are documented on iNaturalist.

birdsfoot trefoil (Lotus corniculatus) at BSU in July 2023
yellow nutsedge (Cyperus esculentus) at BSU in August 2023
velvetleaf (Abutilon theophrasti) at BSU in September 2023
chicory (Cichorium intybus) at BSU on October 2023
puncturevine (Tribulus terrestris) at BSU in November 2023
bull thistle (Cirsium vulgare) at BSU in December 2023

Additional weeds found on the BSU campus from July – December 2023:

  • Abutilon theophrasti (velvetleaf)
  • Cichorium intybus (chicory)
  • Cirsium vulgare (bull thistle)
  • Cyperus esculentus (yellow nutsedge)
  • Eragrostis cilianensis (stinking lovegrass)
  • Lotus corniculatus (birdsfoot trefoil)
  • Medicago sativa (alfalfa)
  • Melilotus alba (white sweetclover)
  • Solanum nigrum (black nightshade)
  • Sonchus asper (prickly sowthistle)
  • Tribulus terrestris (puncturevine)

Additional weeds observed on the BSU campus by iNaturalist users as of December 2023:

  • Aegilops cylindrica (jointed goatgrass)
  • Bromus diandrus (ripgut brome)
  • Cerastium nutans (nodding chickweed)
  • Chorispora tenella (blue mustard)
  • Elymus repens (quackgrass)
  • Hypericum perforatum (St. John’s wort)
  • Lepidium perfoliatum (clasping pepperweed)
  • Matricaria discoidea (pineappleweed)
  • Ornithogalum umbellatum (star-of-Bethlehem)
  • Vicia tetrasperma (four-seeded vetch)
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Weeds of Boise: Boise State University Campus, part one

If you live in a major city (or even a minor one), there is a good chance it is home to a college or university (perhaps several). Universities tend to take up a lot of space, which means there is often a plethora of landscaping accompanying their buildings, hardscaping, and other impervious surfaces. Among all the turf, flower beds, tree wells, and other greenspaces, there is bound to be a fair share of weeds. In spite of how hard the groundskeepers may work, the campus is not likely to ever be completely weed-free. Lucky for us, this means that institutions of higher learning are excellent places to familiarize ourselves with many of the weed species that occur in our cities, particularly weeds that are common in garden beds and turfgrass.

Near downtown Boise, on the southside of the Boise River, you will find the ever-expanding campus of Boise State University, home of the Broncos and their famous blue turf. According to the internet’s favorite encyclopedia, the campus is 285 acres in size, plenty of space for weeds to grow and abudant opportunities to hunt them out. Tallying the number of weed species in a place like this takes time. The benefit of botanizing for weeds is that you can find them at just about any time of year. While some species only show up in certain seasons, others can be seen practically year-round.

In order to document the weeds of Boise State University, I’m spending the entire year walking the campus listing and photographing the weeds I find. What follows is the first half of what’s been documented so far. I’m including a photograph for each month of the year, as well as a list of what I’ve encountered. In part two, I’ll share a list of any additional weeds found throughout the remainder of the year. While you’re waiting for that, check out the other posts in the Weeds of Boise series.

common groundsel (Senecio vulgaris) at BSU in January 2023
chickweed (Stellaria media) at BSU in February 2023
hairy bittercress (Cardamine hirsuta) at BSU in March 2023
ivyleaf speedwell (Veronica hederifolia) at BSU in April 2023
black medic (Medicago lupulina) at BSU in May 2023
creeping thistle (Cirsium arvense) at BSU in June 2023

List of weeds found on the campus of Boise State University as of June 2023:

  • Ailanthus altissima (tree of heaven)
  • Anthriscus caucalis (bur chervil)
  • Amaranthus retroflexus (redroot pigweed)
  • Arctium minus (lesser burdock)
  • Bassia scoparia (kochia)
  • Bromus tectorum (cheatgrass)
  • Capsella bursa-pastoris (shepherd’s purse)
  • Cardamine hirsuta (hairy bittercress)
  • Ceratocephala testiculata (bur buttercup)
  • Chenopodium album (lamb’s quarters)
  • Chondrilla juncea (rush skeletonweed)
  • Cirsium arvense (creeping thistle)
  • Claytonia perfoliata (miner’s lettuce)
  • Convolvulus arvensis (field bindweed)
  • Conyza canadensis (horseweed)
  • Descurainia sophia (flixweed)
  • Digitaria sanguinalis (crabgrass)
  • Draba verna (spring draba)
  • Epilobium ciliatum (willowherb)
  • Erodium cicutarium (redstem filare)
  • Euphorbia maculata (spotted spurge)
  • Galium aparine (cleavers)
  • Geum urbanum (herb Bennet)
  • Holosteum umbellatum (jagged chickweed)
  • Hordeum jubatum (foxtail barley)
  • Lactuca serriola (prickly lettuce)
  • Lamium purpureum (purple deadnettle)
  • Lepidium sp. (whitetop)
  • Malva neglecta (common mallow)
  • Medicago lupulina (black medic)
  • Oxalis corniculata (creeping woodsorrel)
  • Parthenocissus quinquefolia (Virginia creeper)
  • Plantago lanceolata (narrowleaf plantain)
  • Plantago major (broadleaf plantain)
  • Poa annua (annua bluegrass)
  • Poa bulbosa (bulbous bluegrass)
  • Polygonum aviculare (prostrate knotweed)
  • Portulaca oleracea (purslane)
  • Prunella vulgaris (self-heal)
  • Ranunculus repens (creeping buttercup)
  • Senecio vulgaris (common groundsel)
  • Sonchus sp. (sow thistle)
  • Stellaria media (chickweed)
  • Taraxacum officinale (dandelion)
  • Tragopogon dubius (salsify)
  • Trifolium repens (white clover)
  • Ulmus pumila (Siberian elm)
  • Veronica hederifolia (ivyleaf speedwell)
  • Vulpia myuros (rat’s tail fescue)

Do you frequent the BSU campus? Have you seen anything not on my list? Comment below or send me a message and let me know what you’ve seen and where.

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What Is Cheatgrass and Why Should I Care?

To understand the current state of rangeland wildfires in the Intermountain West, you must first familiarize yourself with a plant commonly referred to as cheatgrass. This annual grass moved into the region over a century ago, and its spread has had a massive impact on the environment, as well as the economy and our way of life. Just the very mention of cheatgrass in the West will get some people’s blood boiling. It’s a menace, a scourge, a pest, and yet it’s here to stay. It’s a result of us being here, yet somehow it’s the invader. Its success is largely due to the way we’ve chosen to operate in this region, yet it’s the one to blame for our troubles. When you really start to learn about this plant, it’s hard not to develop an appreciation for it, despite the tragic ways in which it has shaped our region for the worse. It’s not a plant that is showy or grandiose in any significant way. Everything about its appearance screams for it to be dismissed and overlooked, yet it’s story – at least here in the American West – is larger than life.

cheatgrass (Bromus tectorum) – illustration credit: Selected Weeds of the United States, Agriculture Handbook No. 366 (ARS/USDA)

Bromus tectorum goes by more than a dozen common names, but the ones you tend to hear most often are downy brome and cheatgrass. Downy because of how fuzzy its leaf blades can be and cheat because its presence on wheat farms cheats farmers of their yield. It is distributed widely across Europe, eastern Asia, and northern Africa where it originates, and was introduced to North America in the mid-19th century. How and why it got here isn’t totally clear. It likely had multiple introductions, both as a contaminant in seeds and attached to fur, clothing, packaging materials, etc., as well as intentionally as a forage crop for livestock. Regardless, it managed to establish readily in the east and then quickly spread across the country, spanning the continent by the early 20th century. It found the Great Basin particularly habitable due to its hot, dry summers and cold, wet winters and largely treeless landscape.

Apart from the climate, a significant factor behind cheatgrass’s establishment in the Intermountain West are all the cows. For a number of reasons, the Great Basin isn’t really suitable for largescale farming operations, but livestock grazing is another story. Many of the animals native to the region are grazing animals after all, so why not graze cattle and sheep? But there is a limit. Too many animals stuck in one spot for too long leads to overgrazing, and overgrazed sites take time for the native vegetation to recover. Cheatgrass exploits this opportunity by establishing itself quickly in disturbed and overgrazed locations and begins the process of outcompeting nearby plants for limited water and nutrients. Once it begins to dominate these sites, it has another trick up its sleeve.

Cheatgrass actually makes good forage for livestock early in the spring when it’s green and tender, but that quickly changes as the plants start to dry out and go to seed. By early summer, cheatgrass has completed its lifecycle and what’s left is a dried-up plant that, due to the silica in its cells, does not break down readily. Where cheatgrass is abundant, this means large swaths of standing brown grass as far as the eye can see. What’s more, this dead vegetation is highly flammable, and the slightest spark can set off a roaring blaze that moves quickly across the landscape, igniting everything in its path. In a region where fires once occurred decades apart, they now occur on a nearly annual basis. And because fire had been historically infrequent, the native vegetation is not adapted to regular fire and can take years to recover, whereas cheatgrass bounces right back, again exploiting the void left by the decimation of native plants and is flowering again the following spring. It’s a self-perpetuating cycle, and cheatgrass excels at it.

cheatgrass on fire

Cheatgrass is a winter annual, meaning that it germinates in the fall as soon as moisture becomes available. It then lies mostly dormant, its shallow, fibrous roots still growing as long as the ground isn’t frozen. Employing this strategy means cheatgrass is ready to resume growth at a quick pace as soon as the weather warms in the spring. Its roots spread horizontally in the soil and essentially rob water from nearby, more deeply rooted native vegetation. Its deep green, hairy leaves form a little tuft or rosette and provide early spring forage for livestock, gamebirds, and other grazing animals. As the spring progresses flower stalks form and the plants reach heights of around 2 feet (60 centimeters). Their inflorescence is a prominently drooping, open panicle and each spikelet has between 4-8 florets, each with a single, straight awn. The flowers of cheatgrass are cleistogamous, which means they don’t ever open. Self-pollination occurs inside the closed floret, and viable seeds soon develop. As the plant matures, it takes on a purple-reddish hue, after which it turns crispy and light brown as the seeds disperse.

The stiff awns remain on the seeds and aid in dispersal. They also cause injury to animals that dare consume them, poking into the soft tissues of their mouths. Passing animals are also injured when the awns work their way into their feet, ears, and other vulnerable body parts. The ability of the awns to attach so easily to fur and clothing is one of the reasons why cheatgrass spreads so readily. Wind also helps distribute the seed. A single plant can produce hundreds, if not thousands, of seeds, which are ready to germinate upon dispersal. They remain viable in the soil for only a few short years, but since they germinate so easily and are produced so abundantly, their short lifespan isn’t much of a downside.

dried inflorescence of cheatgrass (Bromus tectorum)

In many ways, cheatgrass is the perfect weed. It is able to grow under a broad range of conditions. Its seeds germinate readily, and the plant grows during a time when most other plants have gone dormant. It excels at capturing water and nutrients. It self-pollinates and produces abundant viable seed, which are reliably and readily dispersed thanks to persistent awns. Disturbed areas are ripe for a plant like cheatgrass, but even nearby undisturbed areas can be invaded as seeds are dispersed there. With the help of fire, cheatgrass also creates its own disturbance, which it capitalizes on by then growing even thicker, more abundant stands with now even less competition from native vegetation. And because it is available so early in the season and is readily consumed by livestock and gamebirds, what motivation is there for humans to totally replace it with something else? As James Young and Charlie Clements ask in their book, Cheatgrass, “How can we come to grips with the ecological and economic consequences of this invasive alien species that can adapt to such a vast range of environmental conditions?” In another section they lament, “cheatgrass represents a stage in transition toward an environment dominated by exotic weeds growing on eroded landscapes.”

The topic of cheatgrass and other introduced annual grasses, as well as the even broader topic of rangeland wildfires, is monstrous, but it is one that I hope to continue to cover in a series of posts over the coming months and years. It’s not an easy (or necessarily fun) thing to tackle, but it’s an important one, especially for those of us who call the cheatgrass sea our home.

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Weeds of Boise: Hellstrip on Jefferson Street

Growing plants in urban areas comes with a variety of challenges. Soil conditions aren’t always ideal; shade thrown by buildings and other structures can be difficult to work around; paved surfaces lead to compaction and, among other things, can increase temperatures in the immediate area; and in locations where water is limited, keeping plants hydrated is a constant concern. One location that tends to be especially difficult for gardeners is the hellstrip – the section of ground between a roadway and a sidewalk. Much can be said about gardening in hellstrips, so much that there is even a book about it called Hellstrip Gardening by Evelyn Hadden, which I spent several posts reviewing a few years back.

The difficulty of maintaining a hellstrip (and perhaps questions about who is responsible for maintaining it in the first place) can result in it being a piece of property frequently subject to neglect. In urban areas, neglected land is the perfect place for weeds to take up residence. The conditions in a hellstrip being what they are – hot, dry, frequently trampled, and often polluted – also gives weeds a chance to show what they can do. It’s a wonder that any plant can survive in such conditions, but the wild flora of our cities consists of some pretty tough plants, and a hellstrip is an excellent location to familiarize yourself with some of these plants.

On a walk with Kōura, I came across a weedy hellstrip on Jefferson Street in downtown Boise. Many of the classic hellstrip challenges are present there – it’s surrounded by paved surfaces, there is lots of foot traffic in the area, parking is permitted on the roadside, urban infrastructure (street signs, parking meters, stoplights) is present within the strip. It’s clear that at one point the area was being maintained as irrigation is installed and there are remnants of turfgrass. Three honey locusts were also planted in the strip, one of which has clearly died. Now that maintenance seems to have ceased, weeds have become the dominant flora in this hellstrip. What follows are a few photos and a list of the weeds I’ve identified so far. Like all posts in the Weeds of Boise series, this list may be updated as I continue to check back in on this location.

shepherd’s purse (Capsella bursa-pastoris) and prickly lettuce (Lactuca serriola)
dandelion (Taraxacum officinale)
salsify (Tragopogon dubius)
seed head of salsify
knotweed (Poylgonum sp.)
prickly lettuce (Lactuca serriola)
mallow (Malva neglecta)
orchard grass (Dactylis glomerata)
  • Bromus tectorum (cheatgrass)
  • Capsella bursa-pastoris (shepherd’s purse)
  • Dactylis glomerata (orchard grass)
  • Epilobium brachycarpum (tall willowherb)
  • Lactuca serriola (prickly lettuce)
  • Malva neglecta (dwarf mallow)
  • Polygonum sp. (knotweed)
  • Salsola sp. (Russian thistle)
  • Taraxacum officinale (dandelion)
  • Tragopogon dubius (salsify)
  • Trifolium repens (white clover)
  • Vulpia myuros (rattail fescue)

Are there unkept hellstrips in your neighborhood? If so, what weeds have you seen taking up residence there?

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Weeds of Boise: Vacant Lot on West Kootenai Street

Every urban area is bound to have its share of vacant lots. These are sites that for whatever reason have been left undeveloped or were at one point developed but whose structures have since been removed. The maintenance on these lots can vary depending on who has ownership of them. Some are regularly mowed and/or treated with herbicide, while others go untouched for long periods of time. Even when there is some weed management occurring, vacant lots are locations where the urban wild flora dominates. Typically no one is coming in and removing weeds in an effort to cultivate something else, and so weeds run the show.

As with any piece of land populated by a diverse suite of wild plants, vacant lots are dynamic ecosystems, which you can read all about in the book Natural History of Vacant Lots by Matthew Vessel and Herbert Wong. The impact of humans can be seen in pretty much any ecosystem, but there are few places where that impact is more apparent than in a vacant lot. In lots located in bustling urban centers, human activity is constant. As Vessel and Wong write, “numerous ecosystem interactions are affected when humans intervene by spraying herbicides or insecticides, by trampling, by physically altering the area, or by depositing garbage and waste products.” These activities “can abruptly alter the availability and types of small habitats; this will in turn affect animal as well as plant diversity and population dynamics.” The dynamic nature of these sites is a reason why vacant lots are excellent places to familiarize yourself with the wild urban flora.

Kōura relaxing in a vacant lot

On our morning walks, Kōura and I have been visiting a small vacant lot on West Kootenai Street. We have watched as early spring weeds have come and gone, summer weeds have sprouted and taken off, perennial weeds have woken up for the year, and grass (much of which appears to have been intentionally planted) has grown tall and then been mowed with some regularity. Someone besides us is looking after this vacant lot, and it’s interesting to see how the plant community is responding. As Vessel and Wong note, “attempts to control weedy plants by mowing, cultivating, or spraying often initiate the beginning of a new cycle of growth.” For plants that are adapted to regular disturbance, measly attempts by humans to keep them in check are only minor setbacks in their path to ultimate dominance.

What follows are a few photos of some of the plants we’ve seen at the vacant lot on Kootenai Street, as well as an inventory of what can be found there. This list is not exhaustive and, as with other Weeds of Boise posts, will continue to be updated as I identify more species at this location.

dandelion (Taraxacum officinale)
grape hyacinth (Muscari armeniacum)
henbit (Lamium amplexicaule)
wild barley (Hordeum murinum) backed by cheatgrass (Bromus tectorum)
narrowleaf plantain (Plantago lanceolata) and broadleaf plantain (Plantago major)
perrennial sweet pea (Lathyrus latifolius) surrounded by redstem filaree (Erodium cicutarium)
whitetop (Lepidium sp.)
white clover (Trifolium repens)
  • Bromus tectorum (cheatgrass)
  • Capsella bursa-pastoris (shepherd’s purse)
  • Ceratocephala testiculata (bur buttercup)
  • Convolvulus arvensis (field bindweed)
  • Descurainia sophia (flixweed)
  • Draba verna (spring draba)
  • Erodium cicutarium (redstem filaree)
  • Geum urbanum (wood avens)
  • Holosteum umbellatum (jagged chickweed)
  • Hordeum murinum (wild barley)
  • Lactuca serriola (prickly lettuce)
  • Lamium amplexicaule (henbit)
  • Lathyrus latifolius (perennial sweet pea)
  • Lepidium sp. (whitetop)
  • Malva neglecta (dwarf mallow)
  • Medicago lupulina (black medic)
  • Muscari armeniacum (grape hyacinth)
  • Plantago lanceolata (narrowleaf plantain)
  • Plantago major (broadleaf plantain)
  • Poa bulbosa (bulbous bluegrass)
  • Poa pratensis (Kentucky bluegrass)
  • Rumex crispus (curly dock)
  • Taraxacum officinale (dandelion)
  • Tragopogon dubius (salsify)
  • Trifolium repens (white clover)
  • Veronica sp. (speedwell)

If you live in an urban area, chances are good there is a vacant lot near you. What have you found growing in your neighborhood vacant lot? Feel free to share in the comment section below.

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In Praise of Vagabond Plants – A Book Review

A weed is a highly successful plant that shares a close relationship with humans. In many instances, weeds are seen as nuisance plants, interfering with the goals and intentions we have for a piece of land. In natural areas, they are blamed for, among other things, threatening the existence of the native flora, despite the fact that human activity and disturbance brought them there in the first place and continued human disturbance helps keep them there. In some instances, such as a vacant lot in an urban area, they pose no threat and their existence causes little if any harm, yet they are disparaged for being unsightly, hazardous, and out of place. Nevermind the fact that they are offering a number of ecosystem services free of charge.

For all these reasons and more, weeds get called some pretty nasty things and are the recipient of an unduly amount of ire. The extent that some of us will go to vilify a plant is a bit disturbing to me, so it’s always refreshing to come across a more reasonable approach to weeds. That tempered take is what I found in Gareth Richards’ book, Weeds: The Beauty and Uses of 50 Vagabond Plants, a production of the Royal Horticultural Society and whose vast archives were used to beautifully illustrate the book.

There seems to be a growing trend in the U.K. and other parts of Europe to be more accepting of weeds, to see them as part of our urban, suburban, and exurban flora, and to focus on the value they may bring rather than constantly reviling them as interlopers and thus trying to blast them out of existence with chemical warfare. (See also Wild About Weeds by Jack Wallington). I hope this is true, and I hope the trend continues and catches on in other parts of the world. As Richards writes, “Often the only crime a plant has committed is growing too well.” Thankfully, books like this help bring awareness to these highly fecund and robust plants and their many redeeming qualities.

Richards’ book starts out with a brief introduction and then proceeds with short profiles of 50+ different plant species that are commonly considered weeds. The focus of the book is on weeds found in the U.K.; however, weeds being what they are, at least a few (if not most) of the plants covered are bound to be growing near you regardless of where you live in the world. While there is some discussion of the invasive nature of a few of the plants profiled and the illegality of growing or transporting them – see Japanese knotweed, Himalayan balsam, and pontic rhododendron for example – the focus is not on management nor control. Instead, the discussion revolves around interesting aspects of the plants that makes them worth getting to know rather than something to simply eliminate.

As is often the case when discussing specific plants, medicinal uses and edibility feature heavily in Richards’ plant profiles. It’s interesting to learn about the many ways that humans have thought about and used plants historically, and some of the ways they were historically used are certainly still relevant today; however, many medicinal claims don’t stand the test of time nor do they have empirical evidence to back them up. For this reason, I generally take medicinal uses of plants with a grain of a salt and a healthy dose of skepticism. Edibility, on the other hand, has always been interesting to me, and just when I thought I had heard all the ways that dandelions can be eaten, Richards introduces me to another: “You can even harvest the flower buds for pickling; they make a useful homegrown caper substitute.”

What follows are a few excerpts from the book with accompanying photos of the plants in question.

Ground elder (Aegopodium podagraria) was originally introduced to gardens for its medicinal and edible qualities, but its aggressive behavior can be frustrating. Richards notes, “A useful plant for brave gardeners!”
The rhizomatous nature of yarrow (Achillea millefolium) makes it an excellent addition or alternative to turf grass, and thanks to its drought-tolerance, Richards asserts, “certainly lawns containing yarrow stay greener for longer in dry spells.
Speaking of lawns, “Creeping buttercup (Ranunculus repens) in your lawn is generally a sign that it’s too wet for short grass to thrive.” Richards recommends letting it become a meadow instead. “Sometimes the most rewarding way of gardening is to let nature do it for you.”
Regarding teasel (Dipsacus spp.), Richards writes: “It’s not only bees that adore them; when the seeds ripen they’re loved by birds, especially goldfinches. Try planting some in your garden as a homegrown alternative food source to replace shop-bought nyjer seed.” (photo credit: Sierra Laverty)
“Cats and dogs seek out couch grass (Elymus repens) when they want to chew on something – either for its minerals or to help them vomit to clear their stomachs, often of furballs.” Kōura can frequently be found chewing on it.
“Like many weeds, herb bennet (Geum urbanum) has some clever adaptations. Its nondescript leaves blend seamlessly with other plants, never drawing attention to themselves. And those [clove-scented] roots are really tough, making plants physically difficult to pull up by hand. … The seeds have small hooks and readily attach themselves to fur and clothing to hitch a free ride to pastures new.”

Regardless of how you feel about weeds, if you’re interested in plants at all, this book is worth getting your hands on and these plants are worth getting to know. They may not be the plants you prefer to see growing on your property, but they have interesting stories to tell and, in many cases, may not be as big of a problem as you originally thought. In discussing Spanish bluebells (Hyacinthoides hispanica) and its weedy relatives, Richards hits on a point that for me is one of the main takeaways of this book: “In an age where gardens are becoming wilder and the countryside ever more fragmented, and nature is on the march due to climate change, perhaps we should just learn to treasure the wild plants that thrive in the the new conditions we have made – wherever they originally came from.”

More Weeds Themed Book and Zine Reviews:

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The Wonderful World of Plantlets, Bulbils, Cormlets, Tubercles, and Gemmae

Probably the most well known strategy that plants have for dispersal is by way of seeds. Seeds are plants in embryo, and new generations of plants are born when seeds, released from their parent plants, find suitable locations to germinate. But one of the most amazing things about plants in general is that they have the ability to reproduce in a variety of different ways, and many plant species are not limited to seeds as their only means of dispersal. A paper by Scott Zona and Cody Coyotee Howard, published in Flora (February 2022), introduces us to the intriguing world of aerial vegetative diaspores – just one of the many ways that plants have to get around.

A diaspore is a plant structure that facilitates dispersal. Seeds are diaspores, as are spores, which are produced by non-seed bearing plants like mosses and ferns. If you’ve ever planted bulbs, you’ve handled another type of diaspore. Bulbs and corms, which many spring flowering plants are grown from, form little offshoots called bulblets and cormels that, when detached from their parent structure, can grow into new individuals. These vegetative diaspores are produced below ground. Aerial vegetative diaspores, on the other hand, are formed on above ground plant parts. This clunky term encompasses a number of different structures that are often simply called bulbils, which Zona and Howard explain is used as “a catch-all term that obscures their morphological identity.”

Compiling a list of plant species that feature aerial vegetative diaspores is a difficult task when plant descriptions from various sources use a broad selection of terminology for the same or similar plant parts. To help complete this task, Zona and Howard defined five distinct types of aerial vegetative diaspores – plantlets, bulbils, cormlets, tubercles, and gemmae – and came up with a list of 252 taxa that are known to feature at least one of these structures.

plantlets on the leaf margin of Kalanchoe daigremontiana (wikimedia commons; Aurélien Mora)

Plantlets are miniature plants attached to another plant. Once mature, they have clearly visible leaves, stems, and roots (or root initials) and are non-dormant, meaning they are ready to grow on their own as soon as they’re given the opportunity. The tiny plants borne along the margins of the leaves of mother of thousands (Kalanchoe daigremontiana) is a great example of a plantlet.

A bulbil consists of a shortened stem surrounded by scale leaves modified for food and water storage. Sometimes root initials are visible at the base of the bulbil. Bulbils remain dormant until they are dispersed and conditions are suitable for growth. When bulbils start growing but remain attached to the plant, they become a plantlet. A good example of a bulbil can be found on bulbous bluegrass (Poa bulbosa).

Cormlets are comprised of stem tissue and, like plantlets and bulbils, have a single axis of polarity. They have highly reduced scale leaves and are dormant at dispersal. Bulbil bugle lily (Watsonia meriana), despite its misleading common name, is a good example of a plant that produces cormlets.

Tubercles are made up of swollen stem tissue and, like tubers (their underground counterparts), have multiple shoot buds and multiple axes of polarity (meaning there is no right side up like there is in plantlets, bulbils, and cormlets). They lack scale leaves and are dormant at dispersal. Air potato (Dioscorea bulbifera) is an example of a tubercle-producing plant. As you might guess from the common name, potato-like structures are produced aerially on this vining plant that was introduced to North America from Africa and is now invasive in Florida.

A gemma is a tiny cluster of undifferentiated cells. Gemmae are non-dormant and lack polarity. They are the smallest and least common form of aerial vegetative diaspore and can be found on Drosera pygmaea, a species of sundew native to parts of Australia and New Zealand.

Drosera pygmaea (wikimedia commons; Björn S…)

Zona and Howard’s list of plants with aerial vegetative diaspores is the most comprehensive list to date – although it is undoubtedly and understandably missing some – and includes representatives from 42 plant families and 21 plant orders. Plantlets are the most common form of aerial vegetative diaspore at 116 taxa, with bulbils coming in second at 72. Cormlets and tubercles are less common, with 25 and 16 taxa respectively. Their paper includes the full list and offers further information about many of the species listed. It’s worth taking time to explore and is a valuable resource for anyone interested in the topic. In addition, their discussion section highlights a number of questions that warrant further investigation.

Questions surrounding reproductive strategies and the dispersal of aerial vegetative diaspores are particularly interesting. Because these structures are vegetative, they are essentially clones of the parent plant, meaning there is no genetic mixing as occurs when seeds are produced. This can be an advantage when sexual reproduction isn’t possible due to lack of pollinators, environmental restrictions, or chromosomal/polyploidy anomalies. It also assures that new individuals are pre-adapted to the site, and it can help a species colonize an area quickly. This ability to rapidly colonize explains why several of the species on Kona and Howard’s list are known to be invasive in parts of the world outside of their native range.

A species that produces both seeds and aerial vegetative diaspores may have an advantage when it comes to dispersal since both types of diaspores have their strengths. Seeds can remain dormant in the soil and are likely to persist in the environment longer than vegetative diaspores, but vegetative diaspores can be produced without relying on pollinators and can establish new individuals quickly. The modes of dispersal between the two can also vary. Seeds can be dispersed by wind or carried away by animals, while vegetative diaspores often rely solely on gravity to get around. One exception is hitchhiker elephant ear (Remusatia vivipara), whose bulbils are equipped with tiny hooks that cling to animal fur and are transported in a similar manner to burs.

hooked bulbils of hitchhiker elephant ear (Remusatia vivipara) (wikimedia commons; Dinesh Valke)

When the advantages of aerial vegetative diaspores are considered, it is a wonder that we don’t see them more often. Many plants can be easily propagated by taking stem, leaf, and/or root cuttings and placing them in conditions that favor adventitious root and shoot growth. This may suggest that dormant genetic pathways for producing vegetative diaspores exist in most plants. Or maybe not. Genetic studies of species that feature these structures are needed in order to understand why they are found in some species and not others. Kona and Howard leave us with a slew of research questions like this, and it’s a topic I’ll continue to check in on.

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