Eating Weeds: Cleavers Coffee

One of the world’s most beloved beverages comes from a species of plant found in the fourth largest family of flowering plants. Rubiaceae, also known as the coffee or bedstraw family, consists of around 13,500 species, placing it behind just Asteraceae, Orchidaceae, and Fabaceae for the most number of species. Coffea arabica, and other species in the genus Coffea, are grown for their fruits which are used to make coffee. This makes Rubiaceae one of the most economically important plant families. A family this size is bound to be home to a weed or two, and in fact, one of the most widespread and obnoxious weeds is also a member of Rubiaceae.

Galium aparine, known commonly by a slew of names including cleavers, occurs naturally across large portions of Europe, Asia, North Africa, and possibly even parts of North America. It has been introduced as a weed in many locations across North America, South America, Australia, New Zealand, Japan, and parts of Africa. It is of particular concern in agricultural settings where its lengthy, sprawling branches and sticky leaves get tangled up in harvesting equipment, while its tiny, prickly fruits get mixed in with seeds of similar size like canola.

Galium aparine

Sticky willy, as it is also known, is an annual plant that, in some cases, can have two generations per year – one in the spring (having germinated the previous fall) and one in the summer. Its stems are square, though not as sharply square as plants in the mint family, and can grow to around six feet long. They are weak, brittle, and don’t stand upright on their own; instead they are found scrambling across the ground or, when given the opportunity, climbing up the lengths of other plants in order to reach the sunlight. Leaves occur in whorls of six to eight and are simple and slender with entire margins. Flowers are produced at leaf axils along the lengths of the branches and are tiny, four-petaled, star-shaped, and greenish white. Fruits are borne in pairs and are round, single-seeded, indehiscent nutlets. The stems, leaves, and fruits are covered in stiff, hooked hairs or trichomes, earning it other names like catchweed bedstraw, grip grass, stickyweed, and velcro plant.

flowers and immature fruit on Galium aparine

Galium aparine is a climbing plant, but unlike other climbing plants, it doesn’t twine up things or produce structures like tendrils to hold itself up. Instead, its ability to climb is made possible by its abundant bristly hairs. A paper published in Proceedings of the Royal Society B (2011) investigates the way G. aparine climbs up other plants using the hairs on its leaves. A close inspection of the leaves reveals that the trichomes on the top of the leaf (the adaxial leaf surface) differ significantly from those found on the bottom of the leaf (the abaxial leaf surface). Adaxial trichomes curve towards the tip of the leaf, are hardened mainly at the tip, and are evenly distributed across the leaf surface. Abaxial trichomes curve towards the leaf base, are hardened throughout, and are found only on the midrib and leaf margins.

Having different types of hairs on their upper and lower leaf surfaces gives cleavers an advantage when it comes to climbing up neighboring plants. The authors of the paper describe the technique as a “ratchet mechanism.” When the upper surface of their leaf makes contact with the lower surface of another plant’s leaf, the flexible, outwardly hooked trichomes inhibit it from slipping further below the leaf and allow it to easily slide out from underneath it. When the lower surface of their leaf makes contact with the upper surface of another plant’s leaf, the stiff, inwardly hooked trichomes keep it attached to the leaf even if the other leaf starts to slip away and allows it to advance further across the leaf for better attachment and coverage. Using this ratchet mechanism, cleavers climb up the leaves of other plants, keeping their leaves above the other plant’s leaves, which gives them better access to sunlight. The basal stems of cleavers are highly flexible, which keeps them from breaking as the plant sways in the wind, tightly attached to their “host” plant.

fruits of Galium aparine

The hooked trichomes on the tiny fruits of cleavers readily attach to the fur and clothing of passing animals. The nutlets easily break free from the plants and can be transported long distances. They can also be harvested and made into a lightly caffeinated tea. Harvesting the fruit takes time and patience. I spent at least 20 minutes trying to harvest enough fruits for one small cup of cleavers coffee. The fruits don’t ripen evenly, and while I tried to pick mostly ripe fruits, I ended up with a selection of fruits in various stages of ripeness.

To make cleavers coffee, first toast the seeds for a few minutes in a pan heated to medium high, stirring them frequently. Next, grind them with a mortar and pestle and place the grinds in a strainer. Proceed as you would if you were making tea from loose leaf tea.

The toasted fruits and resulting tea should smell similar to coffee. The smell must not be strong, because my poor sense of smell didn’t really pick up on it. The taste is coffee-like, but I thought it was more similar to black tea. Sierra tried it and called it “a tea version of coffee.” If the fruits were easier to collect, I could see myself making this more often, but who has the time?

The leaves and stems of Galium aparine are also edible, and the plant is said to be a particular favorite of geese and chickens, bringing about yet another common name, goosegrass. In the book Weeds, Gareth Richards discusses the plant’s edibility: “It’s edible for humans but not that pleasant to eat; most culinary and medicinal uses center around infusing the plant in liquids.” Cooking with the leaves or turning them into some sort of spring tonic is something I’ll consider for a future post about eating cleavers.

More Eating Weeds Posts on Awkward Botany

Randomly Selected Botanical Terms: Glochids

The spines of a cactus are an obvious threat. They are generally sharp, smooth, and stiff; as soon as you are stabbed by one, it is immediately clear that you’ve gotten too close. Sitting at the base of the spines – or in place of spines – on many species of cacti is a less obvious, but significantly more heinous threat. Unless you’re looking closely, this hazard is practically invisible, and the pain and irritation that can come as a result of close contact has the potential to last significantly longer than the sharp poke of a spine. This nefarious plant part is called a glochid, and if you’ve ever made contact with one (or more likely several dozen of them), it’s not something you will soon forget.

Opuntia polyacantha x utahensis

The spine of a cactus is actually a leaf. The area from which a spine emerges from the fleshy, photosynthetic stem of a cactus is called an areole, which is equivalent to a node or bud on a more typical stem or branch from which leaves emerge. In place of typical looking leaves, a cactus produces spines and glochids. Like spines, glochids are also modified leaves, although they appear more like soft, little tufts of hair. However, this unassuming little tuft is not to be trifled with.

Close inspection of a glochid (with the help of a microscope) reveals why you don’t want them anywhere near your skin. While the surface of a cactus spine is often smooth and free of barbs, glochids are covered in backwards-facing barbs. The miniscule size of glochids combined with their pliable nature and retrose barbs, make it easy for them to work their way into your skin and stay there. Unlike spines, glochids easily detach from a cactus stem. Barely brushing up against a glochid-bearing cactus can result in getting stuck with several of them.

Opuntia basilaris var. heilii

Because glochids can be so fine and difficult to see, you may not even be aware they are there. You probably won’t even feel them at first. Removing them is a challenge thanks to their barbs, and since you may not be able to remove them all, the glochids that remain in your skin can continue to cause irritation for days, weeks, or even months after contact. For this reason, cactuses are generally best seen and not touched, or at the very least, handled with extreme care.

Apart from being a good form of defense, the glochids of some cactus species can serve an additional function. Most cactus species occur in arid or semi-arid climates, where access to water can be quite limited. In order to increase their chances of getting the water they need, some desert plants are able to collect water from the air. A few species of cactus do this, and glochids are a critical component in making this happen.

Cylindropuntia whipplei

A study published in the Journal of King Saud University – Science (2020) examined the dew harvesting ability of Opuntia stricta, commonly known as erect prickly pear. As described above, the spines of O. stricta are smooth, while the glochids are covered in retrose barbs. Both structures are waterproof due to hardened cell walls and cuticles. However, due in part to the conical shapes of both the glochids and their barbs, water droplets from the air are able to collect on the tips of the glochids. From there, the researchers observed the droplets in their travel towards the base of the glochids. As they moved downward, small droplets combined to form larger droplets.

At the base of the glochids are a series of trichomes, which are small hair-like outgrowths of the epidermis. The trichomes do not repel water, but rather are able to absorb the droplets as they reach the base of the glochids. For a plant species that receives very little water from the soil, being able to harvest dew from the air is critical for its survival, and this is thanks in part to those otherwise obnoxious glochids.

See Also: Prickles

Flowers Strips Bring All the Pollinators to the Yard

The longer I garden the more I gravitate towards creating habitats for creatures that rely on plants for survival. I’ve always been more interested in functional gardens rather than gardens that are simply “plants as furniture” (as Sierra likes to say) – a manicured, weed-free lawn, a few shrubs shaped into gumdrops, sterile flowers for color – and that interest has grown into a way of life. A garden should be more than just something nice to look at, and for those of us who’ve embraced the “messy ecosystems” approach, what’s considered “nice to look at” has shifted dramatically.

Thankfully, I’m not alone in this thinking. Gardens focused on pollinators, birds, habitats, native plants, etc. seem to be gaining in popularity. The question is, is it making a difference? At least one study, referred to below, seems to suggest that it is. And as more gardens like these are planted and more studies like this are done, perhaps we will get a clearer picture of their impact.

In 2017, eight 1000 square meter flower strips were planted in Munich, Germany. The sites had previously been lawn or “roadside greenery,” according to the report published in the Journal of Hymenoptera Research (2020). An additional flower strip, planted in 2015, was included in the study. Over the next year, an inventory of the number of bee species found in these nine flower strips was taken and compared both to the number of bee species that had been recorded in Munich since 1795 (324 species) and the number of bee species recorded in the 20 years prior to the planting of the flower strips (232 species).

In just a year’s time, these newly planted flower strips quickly attracted a surprising number of bees. The researchers identified 68 different species (which is 21% and 29% of the two categories of previously recorded species). As they had expected, most of the bees they identified were common, non-threatened, generalist species; however, they were surprised to also find several species that specialize on pollen from specific groups of plants. Future studies are needed to determine whether or not such flower strips help increase the populations of pollinators in the city, but it seems clear that they are a simple way to increase the amount of food for pollinators, if nothing else.

But perhaps these results shouldn’t be that surprising. Urban areas are not necessarily the biodiversity wastelands that the term “concrete jungle” seems to imply. Though fragmented and not always ideal, plenty of wildlife habitat can be found within a city. In his book, Pollinators and Pollination, Jeff Ollerton lists a number of studies that have been carried out in cities across the world documenting an impressive number of pollinating insects living within their borders [see this report in Conservation Biology (2017), for example]. As Ollerton writes, these studies “show that urbanization does not mean the total loss of pollinator diversity, and may in fact enhance it.” After all, “many of us city dwellers see every day, nature finds a home, a habitat, a place to thrive, wherever it will.”

In a chapter entitled, “The Significance of Gardens,” Ollerton continues to explore the ways in which cities can host a wide variety of flower visiting insects and birds. “Planted patches” don’t necessarily need to be managed as pollinator gardens in order to provide resources for these creatures, nor do all of the plants need to be native to the region to be effective. Rather, diversity in flower structure and timing seems to be key; “floral diversity always correlates with pollinator diversity regardless of the origin of the plants,” Ollerton writes in reference to pollination studies performed in British cities. The more “planted patches,” the better, as “a large and continuous floral display in gardens is the only way to maximize pollinator abundance and diversity.” Add to that, “if you allow some areas to become unmanaged, provide other suitable nesting sites or areas for food plants, and other resources that they need, a thriving oasis for pollinators can be created in any plot.”

ground nesting bee emerging from burrow

Bees and other pollinating insects are finding ways to live within our cities. There is no need to go to the lengths that I like to go in order to help them out. Simply adding a few more flowering plants to your yard, balcony, or patio can do the trick. Eliminating or limiting the use of pesticides and creating spaces for nesting sites are among other things you can do. Learning about specific pollinators and their needs doesn’t hurt either. The continued existence of these creatures is critical to life on earth, and this is one important issue where even simple actions can make a real difference.


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Awkward Botany on Outdoor Idaho (plus Send Us Your Questions)

I spend a lot time on this blog putting weeds in the spotlight, celebrating them for their successes and the unique and interesting plants they are. It’s rare that I get to share these sentiments outside of this particular venue, but I was given such an opportunity recently when asked to talk about weeds for an episode of Outdoor Idaho, a long running show on Idaho Public Television that covers Idaho’s natural history. The theme of this particular episode is wildflowers, so I was intrigued by the idea of coming on to discuss urban weeds. For many, the term “wildflowers” may invoke native plants blooming in natural areas in places far removed from the hustle and bustle of the city. But a wildflower doesn’t have to be a native plant, nor does it have to be growing in the wild. Any plant occurring naturally on its own without the assistance of humans can be a wildflower, and that includes our wild urban flora. I appreciated the chance to share this particular thought with the viewers of Outdoor Idaho.

photo credit: Jay Krajic

Along with me waxing on about weeds, the Wildflowers episode features a host of other Idahoans sharing their thoughts, expertise, and experiences with wildflowers. The episode is brief – coming in at under 30 minutes – but the producers packed in a ton of great wildflower content, and overall I found it to be an excellent representation of the flora of Idaho and a convincing argument for why we should appreciate and elevate these plants. The flora of any region is special and important in its own right, and Idaho’s flora is no different, including its weeds.

Check out Outdoor Idaho’s Wildfowers episode here.

In other news…

If you want to see more of me on the screen (and I’m not sure why you would), Sierra (a.k.a. Idaho Plant Doctor) and I are doing monthly Q&A videos in which we answer your questions about plants, gardening, pests and diseases, insects, or any other topic you might be curious about. You can tune in to those discussions on Sierra’s instagram. If you have questions of your own that you would like us to address, please leave them in the comments section below, or send them to me via the contact page or my instagram.

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)
  • 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)
  • 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.

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:

Dispersal by Open Sesame!

In certain instances, “open sesame” might be something you exclaim to magically open the door to a cave full of treasure, but for the sesame plant, open sesame is a way of life. In sesame’s case, seeds are the treasure, which are kept inside a four-chambered capsule. In order for the next generation of plants to have a chance at life, the seeds must be set free. Sesame’s story is similar to the stories of numerous other plant species whose seeds are born in dehiscent fruits. But in this instance, the process of opening those fruits is fairly unique.

Sesamum indicum is a domesticated plant with a 5000 plus year history of cultivation. It shares a genus with about 20 other species – most of which occur in sub-Saharan Africa – and belongs to the family Pedaliaceae – the sesame family. Sesame was first domesticated in India and is now grown in many other parts of the world. It is an annual plant that is drought and heat-tolerant and can be grown in poor soils and locations where many other crops might struggle. However, the best yields are achieved on farms with fertile soils and adequate moisture.

image credit: wikimedia commons

Depending on the variety and growing conditions, sesame can reach up to 5 feet tall and can be unbranched or highly branched. Its broad lance-shaped leaves are generally arranged directly across from each other on the stem. The flowers are tubular, similar in appearance to foxglove, and are typically self-pollinated and short-lived. They come in shades of white, pink, blue, and purple and continue to open throughout the growing season as the plant grows taller, even as fruits formed earlier mature. The fruits are deeply-grooved capsules with at least four separate chambers called locules. Rows of tiny, flat, teardrop shaped seeds are produced in each chamber. The seeds are prized for their high oil content and are also used in numerous other ways, both processed and fresh. One of my favorite uses for sesame seeds is tahini, which is one of the main ingredients in hummus.

The fruits of sesame are dehiscent, which means they naturally split open upon reaching maturity. Compare this to indehiscent fruits like acorns, which must either rot or be chewed open by an animal in order to free the seeds. Dehiscence is also called shattering, and in many domesticated crop plants, shattering is something that humans have selected against. If fruits dehisce before they can be harvested, seeds fall to the ground and are lost. Selecting varieties that hold on to their seed long enough to be harvested was imperative for crops like beans, peas, and grains. In domesticated sesame, the shattering trait persists and yield losses are often high.

Most of the world’s sesame crop is harvested by hand. The plants are cut, tied into bundles, and left to dry. Once dry, they are held upside down and beaten in order to collect the seeds from their dehisced capsules. When harvested this way, naturally shattering capsules may be preferred. But in places like the United States and Australia, where mechanical harvesting is desired, it has been necessary to develop new, indehiscent varieties that can be harvested using a combine without losing all the seed in the process. Developing varieties with shatter-resistant seed pods, has been challenging. In early trials, seed pods were too tough and passed through threshers without opening. Additional threshing damaged the seeds and caused the harvest to go rancid. Mechanically harvested varieties of sesame exist today, and improvements in these non-shattering varieties continue to be made.

In order to develop these new varieties, breeders have had to gain an understanding of the mechanisms behind dehiscence and the genes involved in this process. This research has helped us appreciate the unique way that the capsules of the sesame plant dehisce. As in the seed bearing parts of many other plant species, the capsules of sesame exhibit hygroscopic movements. That is, their movements are driven by changes in humidity. The simplest form of hygroscopic movement is bending, which can be seen in the opening and closing of pine cone scales. A more complex movement can be seen in the seed pods of many species in the pea family, which both bend and twist as they split open. In both of these examples, water is evaporating from the plant part in question. As it dries it bends and/or twists, thereby releasing its contents.

dehisced capsules of sesame (Sesamum indicum); photo credit: wikimedia commons (Dinesh Valke)

The cylindrical nature and cellular composition of sesame fruits leads to an even more complex form of hygroscopic movement. Initially, the capsule splits at the top, creating an opening to each of the four locules. The walls of each locule bend outward, then split and twist as the seed falls from the capsule. In a study published in Frontiers in Plant Science (2016), researchers found that differences in the capsule’s inner endocarp layer and outer mesocarp layer are what help lead to this interesting movement. The endocarp layer is composed of both transvere (i.e. circumferential) and longitudinal fiber cells, while the mesocarp is made up of soft parenchyma cells. The thicknesses of these two layers gradually changes along the length of the capsule. As the mesocarp dries, the capsule initially splits open and starts bending outwards, but as it does, resistance from the fiber cells in the endocarp layer causes further bending and twisting (see Figure 1 in the report for an illustration). As the researchers write, “the non-uniform relative thickness of the layers promotes a graded bi-axial bending, leading to the complex capsule opening movement.”

All this considered, a rock rolling away from the entrance of a cave after giving the command, “Open sesame!” almost seems simpler than the “open sesame” experienced by the fruit of the sesame plant.

See Also: Seed Shattering Lost – The Story of Foxtail Millet

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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Winter Trees and Shrubs: Tulip Tree

At first glance, a tulip and a tulip tree couldn’t be more different. One is a bulb that puts out fleshy, green leaves in the spring, topped with colorful, cup-shaped flowers, barely reaching a foot or so tall. The other is a massive, deciduous tree with a broad, straight trunk that can grow to nearly 200 feet tall. But if you can get a look at the flowers, seed heads, and even the leaves of this enormous tree, you might see a resemblance – at least in the shape of these features – to one of our most popular spring flowering geophytes.

Tulip tree (Liriodendron tulipifera) is distributed across the eastern United States and has been planted widely outside of its native range. Also commonly known as tulip poplar, yellow poplar, and whitewood, it is a member of the magnolia family and is one of two species in its genus (the other being Liriodendron chinense – a tree found mainly in China). Many (if not most) deciduous trees of North America have small, inconspicuous flowers, but tulip trees – like its close relatives, the magnolias – have relatively large, showy flowers. The trouble is actually getting to see them since, at least on mature trees, they are borne in a canopy that is considerably taller than the average human.

Tulip tree flowers are cup-shaped, yellow-green and orange, with a series of prominent stamens surrounding the carpels which are attached to a long, slender receptacle giving it a cone-shaped appearance. As the flower matures into fruits, the tulip shape of the inflorescence is maintained as the seeds with their wing-like appendages form a tight, cone-like cluster that opens as the seeds reach maturity. The wings aid in dispersal as the seeds fall from the “cone” throughout the winter.

seed head of tulip tree (Liriodendron tulipifera)

The four-lobed leaves of tulip trees also form a vague tulip shape. They are alternately arranged, bright green, and up to five or six inches long and wide, turning yellow in the fall. Two prominent, oval-shaped stipules surround the stem at the base of the petiole of each leaf. These stipules come into play when identifying the leafless twigs of tulip trees during the winter months.

leaf of tulip tree (Liriodendron tulipifera) in late summer

The winter twigs of tulip trees are easily recognizable thanks to their duck bill shaped buds which are made up of two wine-red, violet, or greenish bud scales. The terminal buds are considerably larger and longer than the lateral buds, some of which are on little stalks. The twigs are smooth, olive-brown or red-brown, with just a few, scattered, white lenticels. Leaf scars are rounded with a dozen or so bundle scars that are either scattered or form an irregular ellipse. Pronounced stipule scars encircle the twig at the location of each leaf scar. Twigs can be cut lengthwise to reveal pale white pith that is separated by a series of diaphragms.

winter twig of tulip tree (Liriodendron tulipifera)
top right: the chambered pith of black walnut (Juglans nigra); bottom left: diaphragmed pith of tulip tree (Liriodendron tulipifera)

The bark of tulip trees can be easily confused with that of ash trees. Young bark is smooth and ash-gray to grayish green with pale, vertical cracks. As the tree matures, the cracks develop into furrows with flat-topped ridges. The ridges grow taller and more peaked, and the furrows grow deeper as the tree reaches maturity. In the book Winter Botany, William Trelease compares the mature bark of tulip trees to a series of parallel mountain ranges with deep gullies on either side.

maturing bark of tulip tree (Liriodendron tulipifera)

Perhaps even as tulips are blooming, the buds of tulip trees break to reveal their tulip-shaped, stipule bearing leaves. This makes for an interesting show. In The Book of Forest and Thicket, John Eastman describes it this way: “from terminal buds shaped like duck bills, successions of bills within bills uncurl and unfold, revealing a marvel of leaf packaging.”

More Winter Trees and Shrubs:


The photos of tulip tree were taken at Idaho Botanical Garden in Boise, Idaho.

Burr Tongue, or The Weed That Choked the Dog

It is said that the inspiration for Velcro came when Swiss inventor, George de Mestral, was removing the burrs of burdock from his dog’s coat, an experience we had with Kōura just days after adopting her. I knew that common burdock was found on our property, and I had made a point to remove all the plants that I could easily get to. However, during Kōura’s thorough exploration of our yard, she managed to find the one plant I had yet to pull due to its awkward location behind the chicken coop.

I knew when I saw the clump of burrs attached to her hind end that we were going to spend the evening combing them out of her fur. However, not long after that we discovered that Kōura had already started the process and in doing so had either swallowed or inhaled some. What tipped us off was her violent hacking and gagging as she moved frantically around the living room. She was clearly distraught, and so were we. Recognizing that she had probably swallowed a burr, we made a quick decision to take her to an emergency vet. This was our unfortunately timed (this happened on Christmas Eve) introduction to burr tongue and all the frightening things that can happen when a dog swallows burdock burrs.

The roots, shoots, and leaves of both greater burdock (Arctium lappa) and common burdock (Arctium minus) are edible, which I have already discussed in an Eating Weeds post. The burrs, on the other hand, are clearly not. While sticking to the fur of animals and the clothing of people is an excellent way for a plant to get their seeds dispersed, the sharp, hooked barbs that facilitate this are not something you want down your throat. When this occurs, the natural response is to try to hack them up, which Kōura was doing. Salivating heavily and vomiting can also help. In many cases, this will be enough to eliminate the barbs. However, if they manage to work their way into the soft tissues of the mouth, tongue, tonsils, or throat and remain there, serious infection can occur.

burr of common burdock (Arctium minus)

A paper published in The Canadian Veterinary Journal in 1973 describes the treatment for what is commonly known as burr tongue and technically referred to as granular stomatitis. The paper gives an account of what can happen when “long-haired breeds of dogs … run free in areas where [burdock] grows” and the hooked scales of the burrs consequently “penetrate the mucous membrane of the mouth and tongue.” Dogs with burrs imbedded in their mouths may start eating less or more slowly, drinking more water, and drooling excessively. As infection progresses, their breath can start to stink. A look inside the mouth and at the tongue will reveal lesions where the burrs have embedded themselves. Treatment involves putting the dog under anesthesia, scraping away the infected tissue, and administering antibiotics. Depending on the severity of the lesions, scar tissue can form where the barbs were attached.

To prevent infection from happening in the first place, a veterinarian can put the dog under anesthesia and use a camera inside the dog’s mouth and throat to search for pieces of the burr that may have gotten lodged. There is no guarantee that they will find them all or be able to remove them, and so the dog should be monitored over the next several days for signs and symptoms. At our veterinary visit, the vet also warned us that if any burrs were inhaled into the lungs, they could cause a lung infection, which is another thing to monitor for since it would be practically impossible for an x-ray or a camera to initially find them.

Luckily, now more than three weeks later, Kōura appears to be doing fine, and the offending burdock has been taken care of. One thing is for sure, as someone who is generally forgiving of weeds, burdock is one weed that will not be permitted to grow at Awkward Botany Headquarters.


For more adventures involving Kōura, be sure to follow her on Instagram @plantdoctordog.