Meet Erigeron linearis

Erigeron is a genus of herbaceous, flowering plants consisting of between 390 and 460 species and is a member of the aster/sunflower family (Asteraceae). Plants in this genus are annuals, biennials, or perennials and are mainly found in temperate regions around the world. At least 163 species occur in the contiguous United States. Erigeron diversity is particularly high in western states; however, each state is home to at least one Erigeron species.

A common name for plants in this genus is fleabane. This name comes from an outdated belief that the plants can be used to repel or poison fleas, flies, gnats, and other tiny insects, a belief for which there is no evidence. In Ancient Greek, the name Erigeron is said to mean something akin to “old man in the early morning,” likely referring to the appearance of the seed heads which look like little tufts of white hair. Some Erigeron species are also commonly referred to as daisies.

desert yellow fleabane (Erigeron linearis)

One species of Erigeron that I would like you to meet is Erigeron linearis. While most of the plants in this genus have flowers that are white, pink, or various shades of purple, E. linearis is a yellow-flowered species, hence the common name, desert yellow fleabane. Another common name for this plant is narrow leaved fleabane, a reference to its linear leaves. E. linearis is a small plant with a prominent taproot that reaches up to 20 centimeters tall and forms a leafy, rounded mat or cushion of whitish or gray-green, alternately arranged leaves. The white appearance is due to numerous, fine, appressed hairs on the leaves and stems. Flower stalks are produced in abundance in late spring through early summer and are mostly leafless. They reach above the mound of leaves and are each topped with at least one flower head, which nods at first, but then straightens out as the flowers open. Each flower head is about 2 centimeters wide and is typical of plants in the sunflower family, with a cluster of deep yellow disc florets in the center, surrounded by ray florets that are lighter in color. Both disc and ray florets are fertile; however, the disc florets have both “male” (stamens) and “female” (pistils) flower parts, while the ray florets have only “female” parts. The involucre, which sits at the base of the flowers, is egg-shaped or hemispheric and made up of a series of tiny, fuzzy bracts called phyllaries.

the flower head of desert yellow fleabane (Erigeron linearis)

The fruit of Erigeron linearis is called a cypsela, an achene-like fruit that is characteristic of plants in the sunflower family. The fruits are miniscule and topped with a pappus composed of short outer bristles and longer, pale, inner bristles. The two types of pappus bristles (or double pappus) must be the reason for the scientific name this species was originally given in 1834, Diplopappus linearis. While the seeds of more than 80% of flowering plant species found in dryland regions exhibit some form of dormancy, a study published in Plant Biology (2019), found that E. linearis is one of the few species with non-dormant seeds. This means that for those of us interested in growing plants native to the Intermountain West, E. linearis is a pretty easy one to grow and is a great addition to water-wise gardens, pollinator gardens, and rock gardens.

Erigeron linearis seedling

Erigeron linearis is distributed across several western states and into Canada. It is found in northern California, eastern Oregon and Washington, southern British Columbia, across Idaho and east into southern Montana, western Wyoming and northwestern Utah. It is found at low to moderate elevations in open, rocky foothills, grasslands, sagebrush steppe, and juniper woodlands. It prefers well-drained soils and full sun. It is one of many interesting plants found on lithosols (also known as orthents), which are shallow, poorly develop soils consisting of partially weathered rock fragments. In the book Sagebrush Country, Ronald Taylor calls lithosols “the rock gardens of the sagebrush steppe,” and refers to E. linearis and other members of its genus as “some of the more colorful components of the lithosol gardens.” E. linearis is a food source for pronghorn, mule deer, and greater sage-grouse, and the flowers are visited by several species of bees and butterflies. The plant is also a larval host for sagebrush checkerspots.

desert yellow fleabane (Erigeron linearis)

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Weeds of Boise: iNaturalist Observations

So far, the lists of weeds at each of the Weeds of Boise sites look pretty similar, with several weed species showing up at nearly every site and other species only occasionally making an appearance. This isn’t a surprise really. The flora of any region typically has several species that are dominant, along with species that occur less frequently. Wild urban flora – or in other words, the naturalized weeds in urban areas – may follow a similar pattern. My unscientific and infrequent surveys, all of which have been pretty close to where I live, aren’t yet representative of the Boise area as a whole. However, something like iNaturalist might help with that. For this reason, I took a look at iNaturalist observations to get a better idea as to which species dominate the wild urban flora of Boise, Idaho.

iNaturalist is a website and app that allows users to identify, map, and share observations of living things with the rest of the world. It has been in use for over a decade and is easily one of the most popular community science, biodiversity mapping, and identification apps around. Even though it is not the primary mission of iNaturalist, the information gathered from user observations is frequently used in scientific research and conservation efforts. With over 80 million observations worldwide, iNaturalist offers a pretty decent picture of the plants, animals, fungi, and other living things found in just about any given location. You don’t even need to a registered user to browse the observations and find out what has been spotted near you or across the globe.

In order to come up with a list of weeds that have been observed in Boise by iNaturalist users, I entered “Boise City Metropolitan Area, ID, USA” into the Location field. It is possible to narrow your search to individual neighborhoods or even broaden your search to include a larger area. Clicking on the map allows you to see the area represented in your search. For my purposes, I figured that the number of observations would change if the area covered was either smaller or larger, but the list of weed species would largely remain the same. After you select your search area, you can filter out the results. Clicking on the plant icon limits the search to plants. At first I selected only introduced plants, but that seemed to eliminate a few of the plants that I would consider weeds, so instead I scanned through the entire list of plants and made a list of each of the weed species and how many times each had been observed.

There are of course limitations to using iNaturalist to create species lists, the main one being that you are relying on decisions made by iNaturalist users when it comes to what gets reported. In my case, in which I’m looking for a list of weed species found in Boise, I know there are plenty of weeds that iNaturalist users either aren’t noticing or aren’t bothering to report. The reported observations are also not likely to match the frequency at which they occur in the environment. Still, it’s interesting to see what gets reported and how often. It’s also interesting to see reports of things that I haven’t seen before. By clicking on individual observations, you can see where those observations were made, which means I know where I can go to find species I haven’t yet encountered.

What follows is a list of the top 25 weeds in the Boise area based on the number of iNaturalist observations, along with photos of some of the most reported weeds. A few of the species on the list, like cornflower, straddle the line between weed and desirable plant. I included them anyway because they are known to be naturalized outside of garden borders, even though some of the reported observations may have been intentionally planted within garden borders.

bittersweet nightshade (Solanum dulcamara)
pink-flowered field bindweed (Convolvulus arvensis)
great mullein (Verbascum thapsus)

Top 25 Weeds in the Boise City Metropolitan Area According to iNaturalist Observations (as of September 21, 2021)

  1. great mullein (Verbascum thapsus) – 110 
  2. common dandelion (Taraxacum officinale) – 98
  3. redstem stork’s-bill (Erodium cicutarium) – 83
  4. chicory (Cichorium intybus) – 62
  5. heart-podded hoary cress (Lepidium draba) – 61
  6. cornflower (Centaurea cyanus) – 58
  7. rush skeletonweed (Chondrilla juncea) – 56
  8. purple loosestrife (Lythrum salicaria) – 49
  9. bittersweet nightshade (Solanum dulcamara) – 47
  10. alfalfa (Medicago sativa) – 46
  11. common soapwort (Saponaria officinalis) – 43
  12. dwarf mallow (Malva neglecta) – 42
  13. donkey tail (Euphorbia myrsinites) – 40 
  14. poison hemlock (Conium maculatum) – 39
  15. field bindweed (Convolvulus arvensis) – 39 
  16. bulbous meadow-grass (Poa bulbosa) – 39
  17. yellow salsify (Tragopogon dubius) – 38
  18. crested wheatgrass (Agropyron cristatum) – 37 
  19. cheatgrass (Bromus tectorum) – 36
  20. moth mullein (Verbascum blattaria) – 36 
  21. hound’s-tongue (Cynoglossum officinale) – 31
  22. Virginia creeper (Parthenocissus quinquefolia) – 30
  23. catnip (Nepeta cataria) – 29
  24. white clover (Trifolium repens) – 29
  25. yellow iris (Iris pseudacorus) – 28
Virginia creeper (Parthenocissus quinquefolia)
catnip (Nepeta cataria)
common soapwort (Saponaria officinalis)

Awkward Botanical Sketches #5: Leaves of Yellowstone Edition

Earlier this month, I met up with Eric LoPresti and others at Yellowstone National Park to help take a census of Abronia ammophila, a rare plant endemic to the park and commonly referred to as Yellowstone sand verbena. Abronia (a.k.a. the sand-verbenas) is a small genus of plants in the family Nyctaginaceae that is native to western North America. Several species in the genus have fairly limited distributions, and as the common name implies, members of this genus generally occur in sandy soils. A. ammophila is no exception. A report written by Jennifer Whipple and published in 2002 described it as “restricted to stabilized sandy sites that lie primarily just above the maximum splash zone along the shoreline of [Yellowstone Lake].” Despite the large size of the lake, A. ammophila is not widespread. Most individuals are found along the north shore of the lake, and even there it has been declining. According to Whipple’s report, “Yellowstone sand verbena has been extirpated from a significant portion of its original range along the shoreline of the lake due largely to human influences.”

Like other sand verbenas, A. ammophila has sticky leaves to which sand particles easily adhere, a phenomenon known as psammophory and an act that may help in defense against herbivory. The plant grows prostrate across the sand and produces attractive, small, white, trumpet-shaped flowers in groups of up to 20 that open wide when light levels are low, such as in the evening and in times of heavy cloud cover. The flowers are self-fertile, but insects may also play a role in pollination. It is imperative that questions surrounding its pollination biology, seed dispersal, and other factors regarding its life history are answered in order to halt any further decline of the species and ensure its survival for generations to come.

While in Yellowstone, I enjoyed looking at the all plants, several of which were new to me. I decided to sketch a few of the leaves that I found common around our campsite. I was particularly interested in discolored, diseased, drought-stressed, and chewed-on leaves, since they are more interesting to sketch and color. While I was at it, I attempted to draw a Yellowstone sand verbena seedling as well.

wild strawberry (Fragaria sp.)
Richardson’s geranium (Geranium richardsonii)
lodgepole pine (Pinus contorta)
veiny dock (Rumex venosus)
cinquefoil (Potentilla sp.)
seedling of Yellowstone sand verbena (Abronia ammophila)

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Book Review: In Defense of Plants

Many of us who are plant obsessed didn’t connect with plants right away. It took time. There was a journey we had to go on that would ultimately bring us to the point where plants are now the main thing we think about. After all, plants aren’t the easiest things to relate to. Not immediately anyway. Some of us have to work up to it. Once there, it’s pretty much impossible to go back to our former lives. What was once just a background of green hues is now a rich cast of characters, each with their own name, unique features, and distinct story to tell. Essentially, we went through what Matt Candeias refers to as our ” green revolution.” Candeias – author and host of the long-running blog and podcast, In Defense of Plants – shares his story of learning to love plants and offers a convincing arguement for why you should love them too in his new book, aptly titled, In Defense of Plants.

It’s hard to picture Candeias as anything but a plant lover. If you’ve been following his work, you’ll know he makes it a point to put plants at center stage. It seems that much of the popular content available about plants focuses on the usefulness of plants as they pertain to humans. In many cases it can be easier to find out how to grow a certain plant species than to learn about where it’s from and what it’s like in the wild. Candeias let’s the plants speak for themselves by giving them a voice through his blog, podcast, and now his book. Through the stories he shares we get a peek into the way Candeias sees plants, with the hope being that others might also “be bitten by the botanical bug.”

One of the first plants that captured the attention of Candeias was perennial blue lupine (Lupinus perennis). While assisting with a habitat restoration project at a sand and gravel quarry, Candeias was tasked with improving the establishment of lupine, which is the host plant for the caterpillars of an endangered species of butterfly called Karner blue. The work he did at the quarry and the botanical research that went into it helped Candeias realize that plant’s aren’t at all boring, but are “incredibly interesting organisms worthy of respect and admiration” and that “plants can be both surprisingly relatable and incredibly alien all at once.” His “green revolution” had begun.

The seeds of lupine are dispersed ballistically. As the seed pods dry, tension builds. Then, as Matt Candeias writes in In Defense of Plants, “with an audible pop, the pods eventually explode, catapulting the seeds out into the environment.”

In each chapter of In Defense of Plants we get a peak into the experiences that brought Candeias to where he is now as he discovers the wonder of plants. His personal stories help introduce the main topic of each chapter. Topics include plant sex, plant dispersal, plant defenses, carnivorous plants, and parasitic plants. From countless possible examples, Candeias selects a few of his favorite plant species to help illustrate each topic. Along the way, the reader is presented with various other interesting plant-related facts as Candeias discusses the behaviors of some of the world’s most fascinating plants. In the chapter on dispersal, for example, unlikely agents of seed dispersal (like catfish!) are introduced, as well as phenomena like geocarpy, in which plants are essentially planting themselves.

Carnivorous plants provide an excellent gateway into convincing people who claim to have no interest plants that they actually do. It’s difficult to deny the impressive nature of a meat-eating plant. In the carnivorous plant chapter, Candeias introduces us to the various ways such plants capture and consume their prey, and even wonders if some of these plants should be considered omnivores. After all, certain butterworts digest pollen that falls onto their sticky leaves, and some bladderworts suck in plenty of algae and possibly gain nutrients from the act. If capturing insects inside leaves modified to look like pitchers or on leaves covered in digestive enzyme-producing glands doesn’t impress you, consider the carnivorous actions of corkscrew plants, which drill their leaves into the soil to go after soil-dwelling organisms like protozoans and worms.

Parasitic plants should also excite a reluctant plant lover. These are plants that take all or most of what they need to survive from another plant or host organism. Mistletoes are one of the more familiar parasitic plants, and Candeias describes several, including one that lives almost entirely within the stems of cacti. In fact, “you would never know a cactus had been infected until the mistletoe living within decides to flower,” at which point the flowers push their way out through the sides of the cactus. Dodder is another fairly common, highly specialized, and easy to identify parasitic plant. It basically looks like “a tangled pile of orange spaghetti tossed over the surrounding vegetation.” Orchids, a favorite of Candeias, are known for being mycoheterotrophs, which essentially means they parasitize fungi. Their seeds come unequipped with the energy stores needed to get going, so they borrow resources from mycorrhizal fungi in order to get their start. Years pass before the orchid can offer anything in return.

Datura is a genus of plants that produces toxic compounds like scopolamine and atropine. In his book, In Defense of Plants, Matt Candeias warns, “it would only take a small amount of these chemicals to completely ruin your week and slightly more to put you in a grave.”

After spending more than 200 pages celebrating plants and their amazing abilities and diversity, it’s fitting that Candeias spends the final chapter of his book mourning some of the ways the actions of humans threaten the existence of so many plants. He remarks how unfortunate it is that “plants with their unseeing, unhearing, unfeeling ways of life usually occupy the lowest rung of importance in our society.” Many of us barely notice the loss, yet “plants are the foundation of functioning ecosystems.” Due to that fact, “destroying plant communities causes disastrous ripples that reverberate throughout the entire biosphere of our planet.” Everything suffers when plants are lost. Fortunately, the book doesn’t end on this dark note. Candeias’s overall message is hopeful. When we learn to understand, appreciate, and care about plants, we will want to do everything we can to protect and restore them. With any luck, after reading this book, you too will want to offer your time, energy, and resources in defense of plants.

Listen to Matt talk about his new book on this episode of his podcast.

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Tea Time: Linden Flower Tea

Lindens make great trees for urban areas. A few species and hybrids in particular are commonly planted in parks, yards, and along the streets of cities across the northern hemisphere and have been for decades – centuries even. They cast dense shade, are tolerant of a variety of climates and soil conditions, and are generally easy to maintain. For much of the year as you move throughout the city you live in, you likely pass by dozens of lindens without thinking twice about them. They are ubiquitous, conventional, ordinary, common. Unless they’re in bloom. For a few weeks in early to mid-summer, flowering lindens produce an impossibly sweet fragrance that can’t be ignored. Along with the scent comes the sound of hundreds of buzzing bees collecting pollen and nectar from the pendulous blooms.

Lindens are trees and shrubs in the family Malvaceae and genus Tilia. Around 30 or so species are found in temperate regions across the northern hemisphere, mostly in Europe and Asia. Depending on who you ask, there are between one and three species native to North America. Tilia caroliniana and Tilia heterophylla are considered by some to be varieties of Tilia americana, or American basswood, which is distributed across central and eastern United States and north into parts of Canada. Another common name for linden is lime because words used to refer to the tree in older languages were similar to the word lime. The name basswood comes from the tree’s fibrous inner bark, known as bast.

Linden leaves are generally heart-shaped and asymmetrical with serrate margins. Small clusters of little yellow to white flowers form at the end of a slender stem attached to a narrow, ribbon-like, yellow-green bract. The bract aids in seed dispersal by helping the fruits float on the wind away from the parent tree in a manner similar to the samaras of maple trees. The fruits are small, round, hardened drupes that resemble little peas. The fragrant, nectar-rich flowers are not only favored by beekeepers for honey production, but also have a long history of being harvested for making tea (i.e. tisane). Linden flower tea is said to have a number of medicinal uses and health benefits, all of which I take with a grain of salt. This series of posts isn’t meant to be an investigation into the health claims of plants, but instead an opportunity for me – out of sheer curiosity – to try making tea out of a variety of different plants . If medicinal uses interest you, I encourage you to seek out credible, peer-reviewed sources.

I made linden flower tea from flowers I collected from Tilia cordata, commonly known as littleleaf linden. It was an easy one to find due to its popularity as an urban tree. The natural distribution of littleleaf linden extends from Britain across Europe and into western Asia. Its triangular-ovate shaped leaves are 4-10 centimeters long, glossy green on top, and pale green on the bottom with tufts of orange hairs along the leaf veins, concentrated at the base of the leaf where the leaf blade meets the petiole. The tree can reach up to 21 meters tall and has an oval or rounded-pyramidal shape, though many trees in urban areas are cultivars and can be smaller and more compact.

I harvested the flowers – bracts and all – in late June. It’s advised that they not be harvested directly after a rain (or after being hit by sprinklers), and that they are harvested when the flowers are newly opened. I presume this is because the flowers are at their freshest at this point and will be the best for making tea. I layed the flowers out to dry on a clean kitchen towel on top of a metal cake rack. It only takes 2 or 3 days for them to dry. After drying I removed and saved all the flowers and threw out the bracts and stems, but apparently you can use the entire inflorescence if you’d like.

There are several linden flower tea recipes online. I went with 3 cups of boiling water poured over 1 tablespoon dried linden flowers, covered and steeped for 15 minutes. The resulting tea was an appealing pastel yellow color. I tried it plain as well as sweetened with a little bit of honey. I preferred it sweetened, but unsweetened wasn’t too bad, just a little bitter. It has a floral taste and pleasant smell. Sierra said it tasted earthy, like something she wasn’t supposed to be drinking. Despite that odd review, she said she liked it. Since several sources discussed the calming, sleep-inducing effects of the tea, I made sure to drink it in the evening when it would be normal for me to be feeling sleepy. I suggest you do the same.

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Drought Tolerant Plants: Blue Flax

“Lewis’s prairie flax is a pretty garden ornamental suited to hot, dry sites. Each morning delicate sky blue flowers open on slender arching stems, only to fall off in the afternoon and be replaced by others the next morning. In spite of its fragile appearance, it is quite sturdy and may put out a second flush of blossoms on new growth in late summer.”Common to the This Country: Botanical Discoveries of Lewis and Clark by Susan H. Munger


When selecting plants for a waterwise garden, it is imperative that at least a portion of the plants are easy to grow and maintain and are adapted to a wide variety of conditions. This will ensure a more successful garden, both functionally and aesthetically. Luckily, there are a number of drought-tolerant plants that pretty much anyone can grow without too much trouble. Blue flax, in my opinion, is one such plant.

You may be familiar with flax as a culinary plant, known for its edible seeds which are used to make flour (i.e. meal) and oil. Or perhaps you’ve used linseed oil, a product of flax seeds, to protect wooden, outdoor furniture or in other wood finishing projects. You may also think of linen when you think of flax; and you should, because linen is a textile made from the fibrous stems of the flax plant. All of these products generally come from a domesticated, annual flax known as Linum usitatissimum – a species that has been of benefit to humans for millenia. Various species of flax have also been planted for erosion control, fire breaks, forage for livestock, and in pollinator-friendly gardens. Flax seeds, a common ingredient in bird seed mixes, provide food for birds and other small animals. All this to say, humans and flax share a long history together, and it deserves a place in your garden.

The flax species profiled here is actually two species: Linum lewisii and Linum perenne. That’s because these two species look nearly identical and are both used as garden ornamentals and in wildflower seed mixes. They are also both known as blue flax, among myriad other common names. Due to their similiarity, L. lewisii is considered by some to be a subspecies of L. perenne.

Linum lewisii is found across western North America and received its name after being collected by a member of the Lewis and Clark Expedition. The plant collection was brought back from the expedition and determined to be new to western science. It was described and named by Frederick Pursh. Linum perenne is a European species which was introduced to North America as an ornamental and has since become widely naturalized. In 1980, a naturalized selection of L. perenne was released for use in restoration plantings under the cultivar name ‘Appar’ with the understanding that it was L. lewisii. A genetic study later revealed that the cultivar was instead L. perenne. The study also provided evidence that “North American Lewis flax and European perennial blue flax are reproductively isolated,” suggesting that they are indeed two separate species.

Despite being separate species, telling them apart can be a challenge. Blue flax plants grow from a taproot and woody base and are multistemmed, reaching two to three feet tall. The stems are thin yet stringy, wiry, and not easily torn, which helps explain why flax is such a good plant for making textiles. Short, slender leaves are alternately arranged along the length of the stems, while flower buds form at the ends of stems in loose clusters. Flowers bloom early in the day and are spent by the afternoon. They are 5-petaled, saucer-shaped, and a shade of blue – from whitish blue to deep blue – depending on the plant. Small, round, 10-chambered seed capsules form in the place of flowers, each chamber housing one or two flat, shiny, dark brown seeds. Flowers bloom daily in succession up towards the ends of stems even as the fruits of spent flowers lower on the stalk mature.

seed capsules of blue flax

A close look at their flower parts is really the only way you might be able to tell these two species apart. Blue flax flowers have five stamens topped with white anthers and five styles topped with little, yellow stigmas. The flowers of L. lewisii are homostlyous, which means their styles are all the same length and are generally taller than or about the same height as the stamens. The flowers of L. perenne are heterostylous, which means their flowers can either have styles that are much longer than their stamens or stamens that are much longer than their styles. Each plant in a population of L. perenne has either all long-styled flowers or all short-styled flowers. In a mixed population of L. perenne and L. lewisii, separating the long-styled L. perenne plants from the L. lewisii plants presents a challenge (at least for me).

long-styled blue flax flower
short-styled blue flax flower

Due to the similarity of these two species, it’s easy to see how the plants or seeds of blue flax could easily be mislabeled and sold as one species even though they are the other species. This could be a problem in a restoration planting where seed source and identity is critical, but in your garden, it’s really no big deal. Both species are great for waterwise and pollinator gardens. They are equally beautiful and easy to grow and care for. If nothing else, perhaps the challenge in identifying them will encourage you to take a closer look at your flowers and familiarize yourself with their tinier parts – an act all of us amateur botanists could stand to do more often.

The photos in this post were taken at Idaho Botanical Garden in Boise, Idaho.

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Eating Weeds: Japanese Knotweed

When I first learned that Japanese knotweed was edible, I had my doubts. Sure, lots of plants may be edible, but are they really something you’d want to eat? I know Japanese knotweed as one of the most notorious weeds on the planet. Its destructive, relentless, and prolific nature has landed it on the world’s 100 worst invasive species list, right up there with black rats, Dutch elm disease, and killer algae. Having encountered a fair number of Japanese knotweed stands, the first thing to come to mind has never been, “that looks delicious.” Mature stalks stand as tall as 3 meters with broad, leathery leaves and hollow, bamboo-like stems. Their late summer flowers – a mess of tiny white florets on sprawling flower stalks – are a pollinator’s delight and favored by beekeepers for their abundant nectar. I don’t doubt that the honey produced from such an encounter is tasty, but the plant itself? I needed convincing.

Finally, I looked into it. I came across recipes of Japanese knotweed pickles and learned that it was the young, early emerging shoots that were sought after. That changed my perspective. Certainly you wouldn’t want to gnaw on a woody, 4 foot tall Japanese knotweed stalk, but the tender stems as they’re just beginning to re-emerge from the ground in the spring? Now those might be worth trying.

emerging stems of Japanese knotweed (Reynoutria japonica)

Japanese knotweed (Reynoutria japonica) was introduced to Europe from Japan in the 1800’s, arriving at Royal Botanic Gardens Kew by 1850. At that point, it was a prized ornamental. Its thick stems spotted with reds and purples, its broad, shiny leaves, and its showy flower heads all gave it garden appeal. It was also found to be useful for stabilizing hillsides and reducing erosion, honey production, and as a rhubarb substitute (it’s in the same plant family as rhubarb after all). Not long after that, it made its way to North America. Certainly people must have been aware of its propagative prowess as they moved the plant around. It readily roots from root and stem fragments, plus it produces extensive rhizomes, working their way as deep as 3 meters into the soil and as far as 7 meters away from the parent plant. Perhaps that should have been cause for alarm, but how could anyone have predicted just how aggressive and widespread it would soon become?

Thanks to the plant’s rhizomes, Japanese knotweed grows in thick, many-stemmed stands, pushing out, shading out, and leaving very little room for other plants. The rhizomes are also tough and can push up through gravel, cement, and asphalt. They are notorious for damaging foundations, pipes, and even pushing their way through floorboards. If that’s not enough, Japanese knotweed is pretty much impossible to kill. Herbicides may set it back, but they generally don’t take it out. Cutting it down repeatedly can slow it down, but it may also encourage it to grow more thickly and spread out more widely. Smothering it can work, but you have to be prepared to keep it smothered for quite a while. The deep rhizomes are slow to die, and they may eventually find their way outside of the smothered area, popping up to destroy your efforts to contain it. You can try to dig it out, but the amount of dirt you’d have to dig to get every last root and rhizome really isn’t feasible in most circumstances.

But hey, you can eat it, and perhaps you should. A quick internet search reveals a number of ways the plant can be consumed – purees, chutneys, compotes, sorbets. I chose to go with pickled Japanese knotweed. It seemed simple and approachable enough and a good way to determine if I was going to like it or not. Room temperature brine fermentation is pretty easy. You basically put whatever you’re wanting to pickle in a jar, add whatever spices and things you’d like, fill the jar with salty water, then seal it shut and let it sit there for a few days. Before you know it, you’ve got pickles.

There are several recipes for pickled Japanese knotweed to choose from. I went with this one. The seasonings I used were a bit different, and the stalks I had weren’t as “chubby” as recommended, but otherwise my approach was the same. After a few days, I gave them a try. I was pleasantly surprised. I thought they tasted a little like nopales. Sierra reluctantly tried them and was also surprised by how good they were. They reminded her of pickled asparagus. Other sources describe them as lemony, crunchy, tart and suggest serving them with fish, ramen, or even adding them to a cocktail made with purslane. Many of the weeds I’ve tried have been a fun experience, but not necessarily something I need to repeat. Japanese knotweed pickles, on the other hand, could become a spring tradition for me, and since we’re pretty much stuck with this plant, I’m sure to have a steady supply.

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To Fruit or Not to Fruit – The Story of Mast Seeding

Perennial plants that are able to reproduce multiple times during their lifetime don’t always yield the same amount of seeds each time they reproduce. For some of these plants, there is a stark difference between high-yield years and low-yield years, with low-yield years outnumbering the occasional high-yield years. In years when yields are high, fruit production can seem excessive. This phenomenon is called masting, or mast seeding, and it takes place at the population level. That is, during a mast year, virtually all individuals in a population of a certain species synchronously produce a bumper crop of seeds.

Plants of many types can be masting species. Bitterroot milkvetch (Astragalus scaphoides) and a tussock grass known as Chionochloa pallens are masting species, for example. However, this behavior is most commonly observed in trees, notably nut producing trees like oaks, beeches, and pecans. As you might imagine, the boom and bust cycles of mast seeding plant populations can have dramatic ecological effects. Animals that eat acorns, for example, are greeted with a veritable buffet in a mast year, which can increase their rate of reproduction for a spell. Then, in years when acorns are scarce, the populations of those animals can plummet.

How and why masting happens is not well understood. It is particularly baffling because masting populations can cover considerably large geographic areas. How do trees covering several square miles all “know” that this is the year to really go for it? While a number of possible explanations have been explored, there is still much to learn, especially since so many different species growing in such varied environments exhibit this behavior.

A popular explanation for mast seeding is predator satiation. The fruits and seeds of plants are important food sources for many animals. When a population of plants produces fruit in an unusually high abundance, its predators won’t possibly be able to eat them all. At least a few seeds will be left behind and can sprout and grow into new plants. By satiating their predators they help ensure the survival of future generations. However, even if a plant species has evolved to behave this way, it still doesn’t explain how all the plants in a particular population seem to know when it’s time for another mast year.

Predator satiation is an example of an economy of scale, which essentially means that individual plants benefit when the population acts as a whole. Another economy of scale that helps explain masting is pollen coupling. This has to do with the timing of flowering in cross pollinating species. If individuals flower out of sync with one another, the opportunities for cross pollination are limited. However, if individuals in a population flower simultaneously, more flowers will be pollinated which leads to increased fruit and seed production.  For this to happen, there are at least two factors that come into play. First, the plants have to have enough resources to flower. Making flowers is expensive, and if the resources to do so (like carbon, nitrogen, and water) aren’t available, it won’t happen. Second, weather conditions have to work in their favor. Timing of flowering depends, not only on daylength, but on temperature, rainfall, and other local weather conditions. If individuals across a population aren’t experiencing similar weather, the timing of their flowering may be off.

pollen-producing (male) flowers of pecan (Carya illinoinensis) — via wikimedia commons; Clemson University

Resource matching and resource budgeting are other proposed explanations for masting. Since plants can only use the resources available to them for things like growth and reproduction, they vary each year in how much growing or reproducing they do. Theoretically, if plants in a population are all going to flower in the same year, they all have to have access to a similar amount of resources. Often, the year following a mast year, there is a significant drop in fruit production, as though the plants have used up all of their available resources for reproduction and are taking a break. Some hypothesize that masting is a result of resource storage, and that plants save up resources for several years until they have what they need for yet another big year.

Another thing to consider is how plant hormones might play a role in masting. Gene expression and environmental cues both result in hormonal responses in plants. As Bogdziewicz, et al. write in Ecology Letters (2020), “if hormones and the genes that control them are hypersensitive to an environmental signal, masting can be at least partially independent of resource- and pollen-based mechanisms.” This and other potential explanations for masting are, at this point, largely theoretical. In their paper, Bogdziewicz, et al. propose a number of ways that theoretical predictions can be experimentally tested. If the “research agenda” outlined in their paper is carried out, they believe it will “take the biology of masting from a largely observational field of ecology to one rooted in mechanistic understanding.”

In her book, Braiding Sweetgrass, Robin Wall Kimmerer proposes an additional explanation for the mechanisms behind masting – the trees are talking to one another. Not in the way that you and I might converse, but rather by sending signals through the air via pheromones and underground via complex fungal networks. There is already evidence for this behavior when it comes to plants defending themselves from predators and in sharing resources, so why not in planning when to reproduce? As Kimmerer writes regarding masting, “the trees act not as individuals, but somehow as a collective.” The question now is how.

seedlings of European beech (Fagus sylvatica), a mast-seeding species — via wikimedia commons; user: Beentree

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Winter Trees and Shrubs: Northern Catalpa

The names of plants often contain clues that can either help with identification or that tell something about the plant’s history or use. The name, catalpa, is said to be derived from the Muscogee word, katałpa, meaning “winged head,” presumably referring to the tree’s winged seeds. Or maybe, as one writer speculates, it refers to the large, heart-shaped, floppy leaves that can make it look like the tree is “ready to take flight.” Or perhaps it’s a reference to the fluted, fused petals of the tree’s large, tubular flowers. I suppose it could mean any number of things, but I’m sticking with its seeds, which are packed by the dozens in the tree’s long, slender, bean-like fruits. The seeds are flat, pale brown, and equipped with paper thin, fringed appendages on either side that assist in wind dispersal – wings, in other words.

winged seeds of northern catalpa (Catalpa speciosa)

Catalpa speciosa, or northern catalpa, is a relatively fast growing, short-lived tree native to the Midwest and one of only two species in the genus Catalpa found in the United States. Its distribution prior to the arrival of Europeans appears to have been restricted to a portion of the central Mississippi River valley, extending west into Arkansas, east into Tennessee, and north into Illinois and Indiana. It has since been widely planted outside of its native range, naturalizing in areas across the Midwest and eastern US. Early colonizers planted northern catalpa for use as fence posts, railroad ties, and firewood. Its popularity as an ornamental tree is not what it once was a century ago, but it is still occasionally planted in urban areas as a shade tree. Its messiness – littering the ground below with large leaves, flowers, and seed capsules – and its tendency to spread outside of cultivation into natural areas are reasons why it has fallen out of favor with some people.

The oval to heart-shaped, 8 to 12 inch long leaves with long petioles rotting on the ground below the tree are one sure sign that you’ve encountered a catalpa in the winter time. The leaves are some of the first to fall at the end of the growing season, briefly turning an unmemorable yellow before dropping.

leaf of northern catalpa (Catalpa speciosa) in the winter with soft hairs on the underside still visible

The leaf arrangement on northern catalpa is whorled and sometimes opposite. The twigs are easy to identify due to several unique features. They are stout, round, and grayish brown with prominent lenticels. The leaf scars are large, rounded, and raised up on the twig, looking a bit like little suction cups. They are arranged in whorls of three, with one scar considerably smaller than the other two. A series of bundle traces inside the scar form an ellipse. The leaf buds are tiny compared to the scar and are protected by loose, pointed, brown bud scales. Northern catalpa twigs lack a terminal bud. In the winter, seed capsules or the stalk of an old inflorescence often remain attached to the terminal end of the twig. The pith inside of the twig is thick, white, and solid.

twig of northern catalpa (Catalpa speciosa)

pith inside twig of northern catalpa (Catalpa speciosa)

Another common name for Catalpa speciosa is cigar tree, a name that comes from its up to 18 inch long, cigar-like seed capsules that hang from the otherwise naked tree throughout the winter. The sturdy, cylindrical pod starts out green in the summer and turns dark brown by late fall. Seed pods that haven’t fallen or already split open will dehisce in the spring time, releasing their papery seeds to the wind.

fruits of northern catalpa (Catalpa speciosa) hanging from the tree in the winter

The young bark of northern catalpa is thin and easily damaged. As it matures, it becomes furrowed with either scaly ridges or blocky plates. Mature trees are generally twisted at the base but otherwise grow straight, reaching 30 to 60 feet tall (sometimes taller) with an open-rounded to narrow-oval crown.

maturing bark of northern catalpa (Catalpa speciosa)

Northern catalpa is one of the last trees to leaf out in the spring. In late spring or early summer, 10 inch long clusters of white, tubular flowers are produced at the tips of stems. Before the flowers open, they look a bit like popped popcorn, reminding me of a song from my childhood (which I will reluctantly leave right here). The margins of its trumpet-shaped petals are ruffled and there is yellow, orange, and/or purple spotting or streaking on the inside of the tubes.

flower of northern catalpa (Catalpa speciosa) just before it opens

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Winter Trees and Shrubs: Netleaf Hackberry

Boise, Idaho is frequently referred to as the City of Trees despite being located in a semiarid region of the Intermountain West known as the sagebrush steppe where few trees naturally grow. It earns this moniker partly because the name Boise is derived from the river that runs through it (the Boise River), which was named La Rivere Boisse, or The Wooded River, by early French trappers. Although it flows through a largely treeless landscape, The Wooded River was an apt name on account of the wide expanse of cottonwoods and willows that grew along its banks. The fervent efforts of early colonizers to plant trees in large numbers across their new city also helped Boise earn the title, City of Trees. Today, residents continue the legacy of planting trees, ensuring that the city will remain wooded for decades to come.

As is likely the case for most urban areas, the majority of trees being planted in Boise are not native to the region. After all, very few tree species are. However, apart from the trees that flank the Boise River, there is one tree in particular that naturally occurs in the area. Celtis reticulata, commonly known as netleaf hackberry, can be found scattered across the Boise Foothills amongst shrubs, bunchgrasses, and wildflowers, taking advantage of deep pockets of moisture found in rocky outcrops and draws.

The western edge of netleaf hackberry’s range extends to the northwest of Boise into Washington, west into Oregon, and down into California. The majority of its range is found south of Idaho, across the Southwest and into northern Mexico, then east into the prairie regions of Kansas and Oklahoma. Previously placed in the elm family, it is now considered a member of the family Cannabaceae (along with hemp and hops). It’s a relatively small, broad tree (sometimes a shrub) with a semi-rounded crown. It grows slowly, is long-lived, and generally has a gnarled, hardened, twisted look to it. It’s a tough tree that has clearly been through a lot.

The leaves of Celtis reticulata are rough, leathery, and oval to lance shaped with serrate or entire leaf margins. Their undersides have a distinct net-like pattern that gives the tree its common name. A very small insect called a hackberry psyllid lays its eggs inside the leaf buds of netleaf hackberries in the spring. Its larvae develop inside the leaf, feeding on the sugars produced during photosynthesis, and causing nipple galls to form in the leaves. It’s not uncommon to see a netleaf hackberry with warty-looking galls on just about every leaf. Luckily, the tree doesn’t seem to be bothered by this.

fallen leaves of netleaf hackberry (Celtis reticulata) with nipple galls

The fruit of netleaf hackberry is a pea-sized drupe that hangs at the end of a pedicel that is 1/4 to 1/2 inch long. Its skin is red-orange to purple-brown, and its flesh is thin with a large seed in the center. The fruits, along with a few random leaves, persist on the tree throughout the winter and provide food for dozens of species of birds and a variety of mammals.

persistent fruit of netleaf hackberry (Celtis reticulata)

Celtis reticulata is alternately branched. Its twigs are slender, zig-zagging, and often curved back towards the trunk. They are reddish-brown with several pale lenticels and have sparse, fine, short hairs that are hard to see without a hand lens. The leaf scars are small, half-round, and raised up from the twig. They have three bundle scars that form a triangle. The buds are triangle-shaped with fuzzy bud scales that are slightly lighter in color than the twig. The twigs are topped with a subterminal bud, and the pith (the inner portion of the twig) is either chambered or diaphragmed and difficult to see clearly without a hand lens. 

twigs of netleaf hackberry (Celtis reticulata)

The young bark of netleaf hackberry is generally smooth and grey, developing shallow, orange-tinged furrows as it gets older. Mature bark is warty like its cousin, Celtis occidentals, and develops thick, grey, corky ridges. Due to its slow growth, the bark can be retained long enough that it becomes habitat for extensive lichen colonies.

bark of young netleaf hackberry (Celtis reticulata)

bark of mature netleaf hackberry (Celtis reticulata)

Netleaf hackberry is one of the last trees to leaf out in the spring, presumably preserving as much moisture as possible as it prepares to enter another scorching hot, bone-dry summer typical of the western states. Its flowers open around the same time and are miniscule and without petals. Their oversized mustache-shaped, fuzzy, white stigmas provide some entertainment for those of us who take the time to lean in for a closer look.

spring flowers of netleaf hackberry (Celtis reticulata)

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Photos of netleaf hackberry taken at Idaho Botanical Garden in Boise, Idaho.