Attempts to Avenge the Acts of Cirsium arvense – A Biocontrol Story

Some weeds are so noxious, their crimes so heinous, and their control so challenging that desperation leads us to introduce other non-native organisms to contain them. Alien vs. alien duking it out in a novel environment. It seems counterintuitive – if an introduced species has reached the status of invasive, is it worth the risk of bringing in yet another foreign species in attempt to defeat it? We all know what happened to the old lady who swallowed the spider to catch the fly, yet for decades now we have been doing just this. It’s something we call classical biological control – introducing pathogens, insects, or other organisms to help control the spread of problematic ones.

Such attempts mostly fail, but we keep trying. The attempts made on Cirsium arvense exemplify this. The trouble is that even when such efforts fail, they aren’t always benign, as we shall see.

Canada thistle, a misnomer for Cirsium arvense, is a European native that has been acting in the role of noxious weed for centuries, even in its native land. First introduced accidentally to eastern North America sometime in the 1600’s, it has made its way across the continent and has since become one of our worst weeds in both natural and agricultural settings, as well as in our yards and gardens. Its seeds get around, carried by wind and water, attached to animals or deposited in their dung, stowing away as contaminants in crop seed or passengers in the ballast water of ships. But casual dispersal by seed isn’t quite as troubling as what it does once it takes root.

Several related species of thistle are also pesky weeds, but unlike Cirsium arvense, they are mostly annuals or biennials, spreading only by seed. Cirsium arvense is a perennial plant with roots that spread deep and wide. New shoots form readily along the spreading roots, forming a veritable thicket of stems that can be dozens of feet wide and giving the plant a more appropriate common name, creeping thistle.

The stems of creeping thistle can grow more than four feet tall and are adorned with alternately arranged, prickly, lobed leaves. Groups of small, urn-shaped flowerheads are born at the tops of stems. Flowers are pink to purple, sweet smelling, and favored by pollinators. Individual plants either produce all male flowers or all female flowers, and since individual plants are actually large colonies, an adjacent colony of the opposite sex is necessary in order for the production of viable seeds. Like other plants in the aster family, the seeds come with a feathery pappus, suggesting wind dispersal. However, the pappus is often weakly attached, sloughing off without seeds in tow, leaving them to the fate of gravity.

flowers of creeping thistle (Cirsium arvense) via eol

It comes as no surprise that when plants readily spread by root, stolon, or rhizome, they are well suited to become some of our most bothersome weeds. Eliminating their seed heads does little to reduce their spread. Pulling them out of the ground is futile; you will never get all the roots. Tilling them under only aids in their dispersal since chopped up roots and stems now have the chance to produce new plants. Herbicide treatments can set them back, but they must be repeated on a long-term and exacting schedule in order to thoroughly kill the roots. Considering what we’re up against when it comes to plants like creeping thistle, it makes sense why we would introduce foreign fighters to do our bidding, especially if such fighters are enemies of the plant in their native land.

The list of insects that have been employed (or at least considered) in the fight against creeping thistle is extensive. It includes thistle tortoise beetle (Cassida rubiginosa), seedhead weevil (Rhinocyllus conicus), thistle crown weevil (Trichosirocalus horridus), thistle gall fly (Urophora cardui), thistle stem weevil (Ceutorhynchus litura), thistle bud weevil (Larinus planus), seedhead fly (Orellia ruficauda), thistle flea beetle (Altica carduorum), thistle leaf beetle (Lema cyanella), painted lady (Vanessa cardui), and sluggish weevil (Cleonus piger). Unfortunately, and perhaps not surprisingly, as Bugwood reports, “biocontrol currently provides little or no control of Canada thistle populations, although some agents weaken and kill individual plants.” Despite the fact that there are well over 100 known organisms that consume or attack Cirsium arvense, nothing manages to do long-term damage.

thistle tortoise beetle (Cassida rubiginosa) – a common biocontrol agent of invasive thistle species (via wikimedia commons)

The status of creeping thistle biocontrol efforts on two South Dakota wildlife refuges was reported on in a 2006 issue of Natural Areas Journal. Multiple introductions of at least half a dozen different insect species had occurred beginning in 1986. Nearly 20 years later, they were not found to have had a significant effect on creeping thistle populations. The authors concluded stating they “do not advocate further releases or distribution in the northern Great Plains of the agents” examined in their study. They also advised that “effectiveness be a primary consideration” of any new biocontrol agents and expressed concern that some introduced insects have the potential to attack native thistles.

North America is home to quite a few native thistles, several of which are rare or threatened. A USDA guide to managing creeping thistle in the Southwest highlights the importance of protecting native thistles – “especially rare or endangered species” – from biocontrol agents and gives two examples of endangered thistles in New Mexico that are at risk of such agents.

The federally threatened species, Pitcher’s thistle (Cirsium pitcheri), which is restricted to sand dune shorelines along the upper Great Lakes, has quite a bit working against it. An added blow came a few years ago when it was discovered that the flowerheads of Pitcher’s thistle were being damaged by the thistle bud weevil (Larinus planus), a biocontrol agent employed against creeping thistle in the area. A paper published in Biological Conservation in 2012 examining the extent of weevil damage on the rare thistle cautioned that, “although some biological control agents may benefit some rare plant taxa, the negative impacts of both native insects and introduced herbivores are well documented.”

Pitcher’s thistle (Cirsium pitcheri) via eol

Classical biological control, if and when it works, can be quite valuable, especially if it reduces the need for other management inputs like herbicides and cultivation. Unfortunately, it is rarely successful and can have unintended consequences. Goldson et al. report in a 2014 issue of Biological Conservation that the success rate is only around 10% and that even that 10% is at risk of failing at some point. In his book, Where Do Camels Belong?, ecologist Ken Thompson cites that “only about one in three species introduced as biological controls establish at all, and only half of those that do establish (i.e. about 16% of total attempts) control the intended enemy,” adding that “biological control is just another invasion, albeit one we are trying to encourage rather than prevent, and its frequent failure is another example of how poorly we understand the effects of adding new species to ecosystems.”

Still, while some warn against being too optimistic, others argue that it is an essential tool in the war against invasive species and, while acknowledging that a few introductions have gone awry, assert that “significant non-target impacts” are rare. Clearly, this is a rich topic ripe for healthy debate and one that I will continue to explore. If you have thoughts or resources you’d like to share, please do so in the comment section below.

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This post was inspired in part by episode six of The Shape of the World podcast. I highly recommend listening to the entire series.

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Eating Weeds: Dandelion Flowers

Mention weeds, and the first plant most of us think of is dandelion. It is essentially the poster child when it comes to weeds and one of the few weeds that entire books have been written about. Its notoriety partly comes from being so ubiquitous and recognizable, but it also comes from its utility. It has a long history of being used medicinally and culinarily, and, surprising to some I’m sure, is still grown agriculturally today.

Dandelion is an attractive and useful plant whose main offense is being so accomplished and proficient at staying alive, reproducing, and moving itself around. The principal thing it gets accused of is invading our lawns. With its brightly colored flowers on tall stalks and its globe of feathery seeds, it makes itself obvious, unlike other lawn invaders that tend to blend in more. Once it makes itself at home, it refuses to leave, adding to the frustration. Consider the vats of herbicide that have been applied to turf grass in an attempt to wipe out dandelions. The fact that they hang around, taunting those who care about that sort of thing, helps explain why they are so hated.

common dandelion (Taraxacum officinale)

As Ken Thompson writes in The Book of Weeds, dandelions are “too familiar to need describing,” and since there is already so much written about them, I don’t feel the need to write much myself. Below, instead, are a few excerpts from a handful of books that discuss them.

“It seems many of us possess a conscious will not to believe anything good about this remarkable harbinger of spring which, by its ubiquity and persistance, make it the most recognized and most hated of all ‘weeds.'” — The Dandelion Celebration by Peter Gail

“Dandelion heads consist entirely of overlapping ray florets. … Each floret has its own male and female organs, the (female) style surmounting the (male) stamens. Stamens are unnecessary, however, for the plant to produce seed; much, if not most dandelion seed reproduction occurs asexually (apomixis), without pollen fertilization or any genetic involvement of male cells. But insect pollination (each floret produces abundant nectar in its tubular base) and self-pollination, plus vegetative reproduction via sprouting of new plants from roots and root fragments, also occurs – so this plant has all reproductive fronts covered, surely an important reason for its wide abundance and distribution.” — The Book of Field and Roadside by John Eastman

“Wild violets are too limp and their flowers to insipidly small, too prone to damp, dark corners, as if lacking upright amour propre; in contrast, dandelions are too lush and healthy, their vigorous, indestructible roots, gaudy flowers, and too-plentiful seed heads all too easily spawned with their easygoing means of reproduction by parachute-like seeds, landing where they will, suggesting something of human sexual profligacy.” — Weeds by Nina Edwards

Charles Voysey “The Furrow” (© Victoria and Albert Museum, London

“Dandelions demonstrate evolution in action on suburban lawns. Over several seasons of mowing, the only dandelions that can flower are short-stemmed plants that duck the blade. Mowing thus becomes a selective factor, and in time most of the yard’s surviving dandelion flowers hug the ground.” — The Book of Field and Roadside by John Eastman

“When you stop seeing them as villains, many weeds can be considered as useful plants and certainly have been in the past. Dandelions produce fresh, green leaves nearly all year round. They make a nice addition to a salad, although most people find them too bitter to eat in any quantity. … Dandelion roots are edible too, and have been used in the past as a coffee substitute. If you can find some nice fat burdock roots to go with them, you could even make your own old-fashioned dandelion and burdock drink.” — The Alternative Kitchen Garden by Emma Cooper

“Early medieval Arabian physicians recognized the medicinal properties of dandelion, recorded in Egyptian tombs and described by Theophrastus. Its diuretic effects are mirrored in the common names of pissabed and the French pissenlit; it is recommended for the liver, kidneys, and gallbladder, and even for the treatment of diabetes. In India it is also a traditional remedy for snakebites and its milky sap is said to cure surface tumors and warts, and even unsightly moles and freckles.” — Weeds by Nina Edwards

I ate dandelion flowers blended up with eggs and cooked like scrambled eggs. Its a simple recipe that I adapted from instructions found in the The Dandelion Celebration by Peter Gail. The flowers taste more or less the way they smell. They have a bitterness to them that is akin to their leaves but isn’t nearly as strong. I have eaten dandelion leaves several times and I like them, so the bitterness doesn’t really bother me. If I were to make this again I would use a higher egg to dandelion flower ratio, because even though I enjoyed the flavor, it was a little strong.

Eating Weeds: Clovers

If you ever spent time hunting for four-leaf clovers in the lawn as a kid, in all likelihood you were seeking out the leaves of Trifolium repens or one of its close relatives. Commonly known as white clover, the seeds of T. repens once came standard in turfgrass seed mixes and was a welcome component of a healthy lawn thanks to its ability to fix atmospheric nitrogen and provide free fertilizer. But around the middle of the 20th century, when synthetic fertilizers and herbicides became all the rage, clover’s reputation shifted from acceptable to disreputable. Elizabeth Kolbert, in an article in The New Yorker about American lawns, recounts the introduction of the broadleaf herbicide 2,4-D: “Regrettably, 2,4-D killed not only dandelions but also plants that were beneficial to lawns, like nitrogen-fixing clover. To cover up this loss, any plant that the chemical eradicated was redefined as an enemy.”

white clover (Trifolium repens) in turf grass

This particular enemy originated in Europe but can now be found around the globe. It has been introduced both intentionally and accidentally. Commonly cultivated as a forage crop for livestock, its seeds can be found hitchhiking to new locations in hay and manure. Clover honey is highly favored, and so clover fields are maintained for honey production as well. Its usefulness, however, doesn’t protect it from being designated as a weed. In Weeds of North America, white clover is accused of being “a serious weed in lawns, waste areas, and abandoned fields.”

White clover is a low-growing, perennial plant that spreads vegetatively as well as by seed. It sends out horizontal shoots called stolons that form roots at various points along their length, creating a dense groundcover. Its compound leaves are made up of three, oval leaflets, and its flower heads are globe-shaped and composed of up to 100 white to (sometimes) pink florets. Rich in nectar, the flowers of white clover draw in throngs of bees which assist in pollination. Closely related and similar looking strawberry clover, Trifolium fragiferum, is distinguished by its pink flowers and its fuzzy, rounded seed heads that resemble strawberries or raspberries. Red clover, T. pratense, grows more upright and taller than white and strawberry clovers and has red to purple flowers.

leaves and seed heads of strawberry clover (Trifolium fragiferum)

Clovers are tough plants, tolerating heat, cold, drought, and trampling. Lawns deprived of water go brown fairly quickly, revealing green islands of interlopers, like clover, able to hang in there throughout dry spells. These days, many of us are reconsidering our need for a lawn. Lawns are water hogs that require a fair amount of inputs to keep them green and free of weeds, pests, and diseases. The excessive amounts of fertilizers and pesticides dumped on them from year to year is particularly troubling.

Along with our reconsideration of the lawn has come clover’s return to popularity, and turfgrass seed mixes featuring clover are making a comeback. To keep clover around, herbicde use must be curbed, and so lawns may become havens for weeds once more. Luckily, many of those weeds, including clover, are edible, so urban foragers need only to step out their front door to find ingredients for their next meal.

The leaves and flowers of clover can be eaten cooked or raw. Fresh, new leaves are better raw than older leaves. That being said, clover is not likely to be anyone’s favorite green. Green Deane refers to it as a “survival or famine food” adding that “only the blossoms are truly pleasant to human tastes,” while “the leaves are an acquired or tolerated taste.” In The Book of Field and Roadside, John Eastman remarks: “As humanly edible herbs, clovers do not rank as choice. Yet they are high in protein and vitamins and can be eaten as a salad or cooked greens and in flower head teas. Flower heads and leaves are much more easily digested after boiling.”

I tried strawberry clover leaves and flower heads in a soup made from a recipe found in the The Front Yard Forager by Melany Vorass Herrara. Around two cups of clover chopped, cooked, and blended with potatoes, scallions, and garlic in vegetable or chicken broth is a fine way to enjoy this plant. I don’t anticipate eating clover with great frequency, partly because it is included in a list of wild edible plants with toxic compounds in The North American Guide to Common Poisonous Plants and Mushrooms and also because I have to agree with the opinions of the authors quoted above – there are better tasting green things. Either way, it’s worth trying at least once.

clover soup

More Eating Weeds Posts on Awkward Botany:

Eating Weeds: Burdock

If we agree that weeds can be famous while simultaneously being infamous, a list of famous weeds must include burdock. Its fame largely comes from being an inspiration for the hook-and-loop fastener, Velcro. The idea for this revolutionary product came when Swiss inventor, George de Mestral, was removing burs – the dried inflorescences of burdock – from his dog in the early 1940’s. Most of us have experienced this, pulling out burs from animal hair or our own clothing, but few have felt inspired to develop a new product. Infamy reigns supreme.

But burdock’s fame isn’t tied to Velcro. Its tenacious, sticky burs, which house the seeds, have been attaching themselves to humans and other animals for centuries, frustrating those who have to remove them but finding new places to grow in the process. And what better way to pay tribute to this phenomenon than to dress oneself in hundreds of burs and parade around town calling yourself the Burry Man? Lest you think I’m crazy, just such a thing has been part of an annual celebration for over 300 years in a town outside of Edinburgh, Scotland.

burs of common burdock (Arctium minus)

Of course, burdock is more than its burs. Other, perhaps less celebrated features, are its edible roots and shoots. Its leaves are also edible, but most people find them too bitter to bother. Green Deane suggests wrapping the leaves around food to cook on a campfire. Both the roots and shoots can be eaten raw or cooked, and the fermented roots along with dandelion roots are traditional ingredients in the British beverage, dandelion and burdock. The roots, shoots, and leaves of burdock have also had a wide variety of medicinal uses.

Two species of burdock have become naturalized in North America – Arctium minus and Arctium lappa. Both species are biennials or short-lived perennials. They start out as rosettes of large leaves with woolly undersides. The leaves grow to a foot or more long and wide. At this stage burdock is similar in appearance to rhubarb. Burdock has a large taproot, which can extend down to three feet in the ground. The taproot continues to grow as the rosette expands. When the plant has reached a certain size it begins to put up a branching flower stalk. It is in the rosette stage, before the plant bolts, that the taproot should be harvested.

As the flower stalk grows, the plant takes on a pyramidal shape, with the leaves along the stalk getting increasingly smaller with height. The plant can reach several feet tall, with one source describing them as towering up to ten feet. The stalks should be harvested before the plants start flowering. Multiple flower heads are produced at the ends of the branching stalk. The inflorescences are composed of purple, tubular, disc florets that are encased and encircled in a series of hooked bracts. The flower heads resemble thistle flowers, but the plant is easy to distinguish from thistles due to its large, soft leaves. Speaking of the leaves, one photographer found them alluring enough to compile a series of photos of them.

Common burdock (Arctium minus): the woolly undersides of the leaves and the tops of the taproots

While burdock can be nuisance plant, it is not particularly noxious. In The Book of Field and Roadside, John Eastman writes, “Burdock cannot be labeled a truly invasive weed, for it rarely intrudes into cultivated fields. Tilling usually controls and eradicates burdock populations. Its favored havens are the disturbed soils of roadsides, railroads, fence rows, vacant lots, and around sheds and old buildings.” In Wild Urban Plants of the Northeast, Peter Del Tredici also comments on burdock’s preference for minimally maintained locations including “vacant lots and rubble dump sites; the edges of emergent woodlands; the sunny borders of freshwater wetlands, ponds, and streams; and on unmowed highway banks and median strips with frequent salt applications.”

I harvested my burdock roots along an unmaintained fence line surrounding a series of raised flower beds. I chose a simple recipe for making burdock chips that involved peeling the roots, cutting them into thin slices, dressing them with olive oil and salt, and baking them in the oven. Since the author of this recipe mentioned buying burdock from a store, they were probably using Arctium lappa, or greater burdock, which is commonly cultivated, especially in Asian countries. Both species can be prepared in similar ways.

burdock roots

The burdock chips had a pleasant nutty flavor, but they were also a little stringy and tough to chew. If I were to do it again, I would probably use a recipe like this one that involves parboiling and then frying. Sierra suggested grating the roots and frying them in bacon grease, which would probably do the trick. There are also recipes for pickled burdock roots, which would be fun to try.

Because the plants I harvested were still in their rosette stage and there weren’t any other plants in the area that were bolting, I didn’t try the shoots. But I’ll keep my eye out, and when I find some I may have to write a part two.

Eating Weeds: Lambsquarters

Last year during the Summer of Weeds I inadvertently wrote about several edible weeds, one of which I even ate. It’s not surprising that so many weeds are edible; there are plenty of plants out there – both native and introduced – that are, despite the fact that most of us stick with whatever is made available at the grocery store. Some edible weeds, dandelion included, were once commonly grown for food, while other weeds are close relatives of present day agricultural crops. The more I read about these things and the more my weeds obsession grows, the more I feel compelled to eat them (the edible ones, at least). Hence, a new series of posts: Eating Weeds.

I might as well start with an easy one. Chenopodium album, or lambsquarters, which I wrote about last summer, is a close relative of a number of common crops and a spitting image of quinoa. It happily grows alongside other plants in our vegetable gardens without even being asked to. It is highly nutritious and palatable – particularly the young leaves – and can be eaten raw or cooked. It is often compared to spinach and can be prepared and used in similar ways.

lambsquarters seedling (Chenopodium album)

For the purposes of this post, I decided to try lambsquarters pesto. While pesto is traditionally made using basil leaves, all kinds of other leaves – or combinations thereof – can be substituted. I have made pesto with parsley, which was interesting, as well as watercress, which was delicious. The possibilities are endless. So, why not lambsquarters?

Making pesto is incredibly simple. Blend together a combination of leaves, garlic, nuts or seeds, Parmesan cheese (or something similar), olive oil, salt, and pepper. Pine nuts are traditionally used to make pesto, but like the leaf component, a number of different nuts or seeds can be substituted. I rarely make pesto with pine nuts because, despite being delicious, they are pricey.

lambsquarters pesto

I made two batches of lambsquarters pesto. For the first I used walnuts, and for the second I used sunflower seeds. Both batches were delicious. How could they not be with all of that garlic and cheese in there? Lambsquarters is not a very bitter or strong-tasting green, so lambsquarters pesto might be perfect for anyone who is otherwise not fond of pesto (although that is a stance that I personally cannot fathom).

This is definitely something I will make again. I understand the frustration people have with lambsquarters. It can be prolific and hard to eliminate from a garden. Luckily, it makes an excellent pesto.

Resources:

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This series of posts was inspired in part by the book Dandelion Hunter, in which the author, Rebecca Lerner, attempts to go a full week eating only things she is able to forage in her hometown of Portland, Oregon. As you might imagine, many of the plants she forages are weeds.  

Tiny Plants: Draba verna

Draba verna is a small but memorable plant. Common names for it include early whitlowgrass, vernal whitlowgrass, and spring whitlow-mustard. Sometimes it is simply referred to as spring draba. As these common names suggest, Draba verna flowers early in the spring. It is an annual plant that begins its life by germinating the previous fall. While its flowers are minuscule, multiple plants can be found packed into a single section of open ground, making their presence more obvious. This and the fact that it flowers so early, are what make it so memorable. After a cold, grey winter, our eyes are anxious for flowers, and even tiny ones can be enough.

Draba verna

Draba verna is in the mustard family (Brassicaceae), which is easy to determine by observing its flowers and fruits. The flowers are about 1/8 inch across, with four, deeply-lobed petals. The fruits are oblong, “football-shaped,” flattened capsules that are divided into two chambers and hold up to forty seeds or more. Flowers and fruits are borne at the tips of branched stems that are leafless, hairless, and very thin. Stems arise from a small rosette of narrow leaves that are green to purplish-red and slightly hairy. The plant itself is generally only an inch or two wide and a few inches tall, easily missed other than its aforementioned tendency to be found en masse.

flowers of Draba verna via eol.org

Draba verna occurs throughout much of eastern and western North America, but is said to be introduced from Eurasia. A few sources claim that it is native to North America, but as far as I can tell, that is unverified. Either way, it is naturalized across much of its present range, and even though many of us consider it a weed, it doesn’t seem to be causing too much concern. It’s too tiny and short-lived to really be a problem. It makes its home in disturbed and neglected sites – along roadsides; in fields, pastures, and garden beds; and in abandoned lots. The one place it may be trouble is in nurseries and greenhouses, where it might be able to compete with young plants in pots.

open capsule and seeds of Draba verna via eol.org

The flowers of Draba verna are self-fertile, but they are also visited by bees that have ventured out in early spring. The foliage might by browsed by rabbits and other small mammals, but otherwise this plant is of little use to other creatures. Being in the mustard family, it is likely edible, but again it is so small that harvesting it would hardly be worth it. Instead, maybe its best to leave it in place and enjoy it for what it is: a tiny, brave reminder that spring is on its way and an encouragement to get down low once in a while to admire the little things.

An attempt at sketching Draba verna fruits on a raceme.

See Also: Tiny Plants: Duckweeds

Spring Weeds in the Mustard Family

Is there a plant family that consists of more weedy species than the mustard family? Asteraceae and Poaceae, for sure. Fabaceae or Lamiaceae, perhaps. Regardless, Brassicaceae is replete with dozens of species – mostly annual – that are skilled at taking advantage of the disturbed environments that humans are in the habit of creating.

It helps that the mustard family is so large: 372 genera and over 4,000 species distributed across the globe. Around 55 genera are said to occur in North America. Most of the plants in this family are herbaceous; few are shrubs. Foliage is aromatic, especially when crushed. Flowers are particularly distinctive. Each flower has four petals – in some species petals are divided, giving the impression that there are more than four – arranged in the shape of a cross or “X.” Flowers are often small, have 4 tall stamens and 2 short stamens, and commonly come in white, yellow, pink, or purple. They are arranged on a raceme, which is typically either tall and straight or compact and flat-topped.

Fruits in the mustard family are capsules with two compartments separated by a clear membrane. The capsules may be at least three times longer than they are wide, in which case they are referred to as a silique; or they may be less than three times longer than they are wide and referred to as a silicle. This is a curious distinction, and it doesn’t tell you all that much. It’s more important to understand that the capsules of mustards can come in various sizes and shapes, and that some can be long and narrow while others are short and either round or angular.

mustard seeds via wikimedia commons

Despite the size or shape of the capsule, enclosed are numerous seeds – sometimes dozens. Surely one of the reasons why plants in the mustard family are so successful at proliferating is their ability to produce thousands, even tens of thousands, of seeds per plant. The seeds are typically tiny; and while they may not make it very far from the parent plant, they are numerous. Depending on the species, they can also remain viable for years, affording them the opportunity to sprout whenever conditions are right. You may have heard the biblical verse about faith the size of a mustard seed giving one the ability to move mountains. Size seems irrelevant here, so how about faith as tough, resilient, opportunistic, and resourceful as a mustard seed? If a mountain can be moved, mustards might be the one to do it.

While it isn’t the scope of this post, it’s worth mentioning the chemical compounds present in mustards that give them the flavors and health benefits we enjoy as well as the toxicity that can harm us and any other organisms that dare consume them. Glucosinolates, which are present in various concentrations depending on the species, are a defining characteristic of plants in the mustard family. They contribute to the spicy-ness of things like horseradish, radish, and condiment mustard while also acting as a natural insecticide, deterring herbivory.

And now on to the cast of characters:

Whitetop (Lepidium spp.)

Garlic mustard (Alliaria petiolata) – a noxious weed in many parts of North America – is fortunately not an issue in southwestern Idaho, otherwise it would be first on the list. Instead, we deal with whitetop – a noxious weed in Idaho and several other states. As the common name suggests, individual plants – up to two feet tall – are topped with a dense cluster of tiny, white flowers. Seed production in this group isn’t as abundant as other mustards; instead, the tour de force are their rhizomes. Whitetop is a perennial plant that spreads aggressively via underground stems as well as root fragments and can easily form expansive, dense patches, outcompeting other plants in the area.

Another common name for this group is hoary cress on account of their gray-green, fuzzy foliage. They are further distinguished by the shape of their seed pods: lens-podded hoary cress (L. chalepense), heart-podded hoary cress (L. draba), and globe-podded hoary cress (L. applelianum).

white top (Lepidium sp.)

white top (Lepidium sp.)

Tansymustard (Descurainia spp.)

There are two species of tansymustard (also known as flixweed) that occur in my part of the world, one is native and the other is introduced from Europe. They are indistinguishable to my untrained eye. If I have seen them side by side, I wouldn’t have known it. They are both annuals and can be as short as a few inches to over two feet tall. They have highly dissected, fern-like leaves and tiny, pale yellow or green-yellow flowers. The seed pods are very skinny and around an inch long. Each pod can hold 40 seeds, and a large plant can produce over 75,000 seeds. They are quick to take advantage of disturbed soil and come up in abundance after a fire. I’m not sure what it is about this year, but they have been particularly prolific this spring.

tansymustard (Descurainia sp.)

tansymustard (Descurainia sp.)

Blue Mustard (Chorispora tenella)

Also known as musk mustard or crossflower, this sticky, stinky, annual plant apparently makes cow’s milk taste funny; however some people still enjoy eating it. It can get to about a foot and a half tall, and is adorned with pretty, little, blue-purple flowers. The pointy seed pods split crosswise rather than lengthwise, an uncommon trait in mustards.

blue mustard (Chorispora tenella)

blue mustard (Chorispora tenella)

Desert Madwort (Alyssum desertorum)

Like tansymustard, this species is very similar in appearance to another closely related species, Alyssum alyssoides (commonly known as pale madwort or yellow alyssum). Both are annuals under a foot tall, covered in tiny hairs, with minuscule yellow flowers, and numerous round seed pods. They are adapted to dry, neglected sites.

yellow alyssum (Alyssum dessertorum)

Annual Honesty (Lunaria annua)

If you don’t recognize this plant when it’s flowering, you will when its seed pods ripen. They are thin, round discs up to three inches across. Eventually, the outer layers of the seed pods fall away, and translucent membranes remain, sometimes with seeds still attached. This trait has earned this species common names like money plant and silver dollar. The plants are attractive, reach up to three feet tall, and produce showy, purple flowers, which explains why they are popular ornamentals. However, like other mustards, the proficiency with which they reproduce in abundance via seeds, means they also easily migrate into natural areas and neglected sites.

annual honesty (Lunaria annua)

Hairy Bittercress (Cardamine hirsuta)

This little, quick-growing, fast-spreading annual is a common nuisance in greenhouses and nurseries. On stalks above compact rosettes are borne clusters of white flowers that, as Ken Thompson writes in The Book of Weeds, “are so tiny they are almost invisible.” The slender seed pods burst open at maturity, sending minuscule seeds flying. Brush your hand over a patch of mature hairy bittercress and you will be bombarded.

hairy bittercress (Cardamine hirsuta)

And the list goes on…

I’ve observed several other weedy species in this family recently, but to keep the length of this post reasonable I will just list them here: shepherd’s purse (Capsella bursa-pastoris), clasping pepperweed (Lepidium perfoliatum), spring draba (Draba verna), tumble mustard (Sisymbrium altissimum), and pennycress (Thlaspi arvense). This list only scracthes the surface; there are many other weeds in the mustard family. All deserve to be mentioned, so perhaps another time.

See Also: In Defense of Plants – One Mustard, Many Flavors