Dr. Beal’s Seed Viability Experiment

In 1879, Dr. William J. Beal buried 20 jars full of sand and seeds on the grounds of Michigan State University. He was hoping to answer questions about seed dormancy and long-term seed viability. Farmers and gardeners have often wondered: “How many years would one have to spend weeding until there are no more weeds left to pull?” Seeds only remain viable for so long, so if weeds were removed before having a chance to make more seeds, the seed bank could, theoretically, be depleted over time. This ignores, of course, the consistent and persistent introduction of weed seeds from elsewhere, but that’s beside the point. The question is still worth asking, and the study still worth doing.

When Dr. Beal set up the experiment, he expected it would last about 100 years, as one jar would be tested every 5 years. However, things changed, and Dr. Beal’s study is now in its 140th year, making it the longest-running scientific experiment to date. If things go as planned, the study will continue until at least 2100. That’s because 40 years into the study, a jar had to be extracted in the spring instead of the fall, as had been done previously, and at that point it was decided to test the remaining jars at 10 year intervals. In 1990, things changed again when the period was extended to 20 years between jars. The 15th jar was tested in 2000, which means the next test will occur in the spring of next year.

In preparing the study, Dr. Beal filled each of the 20 narrow-necked pint jars with a mixture of moist sand and 50 seeds each of 21 plant species. All but one of the species (Thuja occidentalis) were common weeds. He buried the jars upside down – “so that water would not accumulate about the seeds” – about 20 inches below ground. Near each bottle he also buried seeds of red oak and black walnut, but they all rotted away early in the study.

After the retrieval of each bottle, the sand and seed mixture is dumped into trays and exposed to conditions suitable for germination. The number of germinates are then counted and recorded. Over the years, the majority of the seeds have lost their viability. In 2000, only three species germinated  – Verbascum blattaria, a Verbascum hybrid, and Malva rotundifolia. There were only two individuals of the Verbascum hybrid, and only one Malva rotundifolia. The seeds of Verbascum blattaria, however, produced 23 individuals, suggesting that even after 120 years, the seeds of this species could potentially remain viable long into the future.

moth mullein (Verbascum blattaria)

In the 2000 test, the single seedling of Malva rotundifolia germinated after a cold treatment. Had the cold treatment not been tried, germination may not have occurred, which begs the question, how many seeds in previous studies would have germinated if subjected to additional treatments? Dr. Beal himself had wondered this, expressing that the results he had seen were “indefinite and far from satisfactory.” He admitted that he had “never felt certain that [he] had induced all sound seeds to germinate.”

There are also some questions about the seeds themselves. For example, the authors of the 2000 report speculate that poor germination seen in Malva rotundifolia over most of the study period could be “the result of poor seed set rather than loss of long-term viability.” The presence of a Verbascum hybrid also calls into question the original source of those particular seeds. A report published in 1922 questions whether or not the seeds of Thuja occidentalis were ever actually added to the jars, and also expresses uncertainty about the identify of a couple other species in the study.

Despite these minor issues, Dr. Beal’s study has shed a great deal of light on questions of seed dormancy and long-term seed viability and has inspired numerous related studies. While questions about weeds were the inspiration for the study, the things we have been able to learn about seed banks has implications beyond agriculture. Seed bank dynamics are particularly important in conservation and restoration. If plants that have disappeared due to human activity have maintained a seed bank in the soil, there is potential for the original population to be restored.

In future posts we will dive deeper into seed banks, seed dormancy, and germination. In the meantime, you can read more about Dr. Beal’s seed viability study by visiting the following links:

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Eating Weeds: Blue Mustard

Spring is here, and it’s time to start eating weeds again. One of the earliest edible weeds to emerge in the spring is Chorispora tenella, commonly known by many names including blue mustard, crossflower, and musk mustard. Introduced to North America from Russia and southwestern Asia, this annual mustard has become commonplace in disturbed areas, and is particularly fond of sunny, dry spots with poor soil. It can become problematic in agricultural areas, but to those who enjoy eating it, seeing it in large quantities isn’t necessarily viewed as a problem.

rosettes of blue mustard (Chorispora tenella)

The plant starts off as a rosette. Identifying it can be challenging because the shape of the leaves and leaf margins can be so variable. Leaves can either be lance-shaped with a rounded tip or more of an egg shape. Leaf margins are usually wavy and can be deeply lobed to mildly lobed or not lobed at all. Leaves are semi-succulent and usually covered sparsely in sticky hairs, a condition that botanists refer to as glandular.

A leafy flower stalk rises from the rosette and reaches between 6 and 18 inches tall. Like all plants in the mustard family, the flowers are four-petaled and cross-shaped. They are about a half inch across and pale purple to blue in color. Soon they turn into long, slender seed pods that break apart into several two-seeded sections. Splitting apart crosswise like a pill capsule rather than lengthwise is an unusual trait for a plant in the mustard family.

blue mustard (Chorispora tenella)

Multiple sources comment on the smell of the plant. Weeds of North America calls it “ill-scented.” Its Wikipedia entry refers to it as having “a strong scent which is generally considered unpleasant.” The blog Hunger and Thirst comments on its “wet dish rag” smell, and Southwest Colorado Wildflowers claims that its “peculiar odor” is akin to warm, melting crayons. Weeds of the West says it has a “disagreeable odor,” and warns of the funny tasting milk that results when cows eat it. All this to say that the plant is notorious for smelling bad; however, I have yet to detect the smell. My sense of smell isn’t my greatest strength, which probably explains why I’m not picking up the scent. It could also be because I haven’t encountered it growing in large enough quantities in a single location. Maybe I’m just not getting a strong enough whiff.

Regardless of its smell, for those of us inclined to eat weeds, the scent doesn’t seem to turn us away. The entire plant is edible, but the leaves are probably the part most commonly consumed. The leaves are thick and have a mushroom-like taste to them. They also have a radish or horseradish spiciness akin to arugula, a fellow member of the mustard family. I haven’t found them to be particularly spicy, but I think the spiciness depends on what stage the plant is in when the leaves are harvested. I have only eaten the leaves of very young plants.

The leaves are great in salads and sandwiches, and can also be sauteed, steamed, or fried. I borrowed Backyard Forager’s idea and tried them in finger sandwiches, because who can resist tiny sandwiches? I added cucumber to mine and thought they were delicious. If you’re new to eating weeds, blue mustard is a pretty safe bet to start with – a gateway weed, if you will.

blue mustard and cucumber finger sandwiches

For more information about blue mustard, go here.

Eating Weeds 2018:

Tiny Plants: Idahoa

This is a post I wrote three years ago as a guest writer for a blog called Closet Botanist. That blog has since dissolved, hence the re-post.

This year, we returned to the location in the Boise Foothills where I encountered the plant that inspired this post. I found what might be seedlings of the tiny plant. If that’s the case, the phenology is a bit delayed compared to three years ago. I’ll check again in a week or so. Until then, meet Idahoa.

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I have taken a real liking to tiny plants. So many of the plants we regularly interact with are relatively big. Large trees loom above us. Tall shrubs greet us at eye level. Flowering perennials come up around our knees or higher. But how often do we get down low and observe the plants that hug the ground or that reach just a few centimeters above it? Turf grass is ubiquitous and groundcovers are common, but among such low growing plants (or plants kept low), even more diminutive species lurk.

It was a hunt for a tiny plant that sent me down a certain trail in the Boise Foothills earlier this spring. Listening to a talk by a local botanist at an Idaho Native Plant Society meeting, I learned about Idahoa scapigera. A genus named after Idaho!? I was immediately intrigued. Polecat Gulch was the place to see it, so off I went.

Commonly known as oldstem idahoa, flatpod, or Scapose scalepod, Idahoa scapigera is the only species in its genus. It is an annual plant in the mustard family, which means it is related to other small, annual mustard species like Draba verna. It is native to far western North America and is distributed from British Columbia down to California and east into Montana. It occurs in a variety of habitat types found in meadows, mountains, and foothills.

Idahoa scapigera is truly tiny. Before it flowers, it forms a basal rosette of leaves that max out at about 3 centimeters long. Next it sends up several skinny flower stalks that reach maybe 10 centimeters high (some are much shorter). One single flower is born atop each stalk. Its petite petals are white and are cupped by red to purple sepals. Its fruit is a flat round or oblong disk held vertically as though it is ready to give neighboring fruits a high five. Happening upon a patch of these plants in fruit is a real joy.

Which brings me to my hunt. It was the morning of March 20th (the first day of Spring) when I headed down the Polecat Gulch trail in search of Idahoa, among other things. The trail forms a loop around the gulch and is about 6 miles long with options for shortening the loop by taking trails that cut through the middle. I have yet to make it all the way around. Stopping every 10 yards to look at plants, insects, and other things makes for slow hiking.

I was about a half mile – 1 hour or more – into the hike when Idahoa entered my view. A group of them were growing on the upslope side of the trail, greeting me just below waist level. Many of them had already finished flowering and had fresh green fruits topping their thin stalks. At this location they are a late winter/early spring ephemeral. I made a mental note of the site and decided to return when the fruits had matured. Next year, I will head out earlier in hopes of catching more of them in flower.

On the way to Idahoa, I noted numerous other small, green things growing in the sandy soil. It turns out there are countless other tiny plants to see and explore. It got me thinking about all the small things that go unnoticed right underneath our feet or outside of our view. I resolved to move slower and get down lower to observe the wonders I’ve been overlooking all this time.

Further Reading:

Poisonous Plants: Red Squill

Humans have been at war with rats since time immemorial. Ridding ourselves of their nuisance behavior is increasingly unlikely, and in fact, some scientists believe that, following human extinction, rats will be poised to take our place as the most dominant species on earth. Despite being thwarted repeatedly, we make tireless attempts to control rat populations. One major weapon in our arsenal is poison, and one of the most popular rat poisons was derived from a plant with a formidable bulb.

Urginea maritima (known synonymously as Drimia maritima, among other Latin names) is a geophyte native to the Mediterranean Basin, where it survives the hot, dry summer months by going dormant, waiting things out underground. Growth occurs in the cooler months, its bulb expanding annually before it finally flowers late one year after reaching at least 6 years old. Its flower stalk rises to as tall as 2 meters, extending heavenward from a bulb that can weigh as much as a kilogram. Its inflorescence is long, narrow, and loaded with small flowers that are generally white, but sometimes pink or red.

The oversized bulb of Urginea maritima — via wikimedia commons

Urginea maritima is commonly known as red squill or white squill (and sometimes simply, squill). Other common names include sea onion, sea squill, and giant squill. It is related the squill referred to in the Harry Potter universe, which is known botanically as Scilla. However, plants in the genus Scilla are much more dimunutive and generally flower in the spring rather than the fall. Like red squill, Scilla species are known to be poisonous; however, they don’t have the reputation for producing deadly rat poison that red squill does.

Like so many poisonous plants, red squill has a long history of being used medicinally to treat all sorts of ailments. As with any folk remedy or natural medicine, a doctor should be consulted before attempting to treat oneself or others. A 1995 report tells of a woman who ate red squill bulbs to treat her arthritic pain. She exhibited symptoms characteristic of ingesting cardiac glycosides – the toxic compound found in red squill – including nausea, vomiting, and seizures. She died 30 hours after eating the bulbs.

red squill (Urginea maritima) — via wikimedia commons

Toxic compounds are found throughout the plant, but are particularly concentrated in the bulb (especially its core) and the roots. Toxicity is at its highest during summer dormancy and when the plant is flowering and fruiting. The compound used to poison rats is called scilliroside. Bulbs are harvested in the summer, chopped up, and dried. The chips are then ground down to a powder and added to rat bait. Results are highly variable, so to increase its effectiveness, a concentrate can be made by isolating the toxic compound using solvents.

Red squill was introduced to southern California in the 1940’s as a potential agricultural crop. The region’s Mediterranean climate and the plant’s drought tolerance made it ideal for the area. The bulbs can be grown for manufacturing rat poison, and the flowers harvested for the cut flower industry. Breeding efforts have been made to produce highly toxic varieties of red squill for rat poison production.

the flowers of red squill (Urginea maritima) — via wikimedia commons

Around the time red squill was being evaluated as an agricultural crop, studies were done not only on its toxicity to rats, but to other animals as well. A 1949 article details trials of a red squill derived poison called Silmurine. It was fed to rats as well as a selection of farm animals.  Results of the study where “not wholly satisfactory” when it came to poisoning rats. Silmurine was less effective on Rattus rattus than it was on Rattus norvegicus. Thankfully, however, it was found to be relatively safe for the domestic animals it was administered to. Most puked it up or avoided it. Two humans accidentally became part of the study when they inadvertently inhaled the poison powder. Ten hours later they experienced headaches, vomiting, and diarrhea, “followed by lethargy and loss of appetite,” but “no prolonged effects.”

Vomiting is key. Ingesting scilliroside induces vomiting, which helps expel the poison. However, rodents can’t vomit (surprisingly), which is why the poison is generally effective on them.

Today, squill is available as an ornamental plant for the adventurous gardener. For more about that, check out this video featuring a squill farmer:

More Poisonous Plants posts on Awkward Botany:

Podcast Review: Botanical Mystery Tour

My interest is piqued any time plants are featured or plugged in popular culture. Hence my ongoing series of posts, Botany in Popular Culture, featuring Futurama, Saga of the Swamp Thing, etc. Plants just don’t get enough airtime, so it must be celebrated when they do. Which is why I was excited to learn about Chicago Botanic Garden‘s new podcast, Botanical Mystery Tour, in which the plants referenced in pop culture take center stage.

The hosts, as they state in each episode’s introduction, “dive into the botany hidden in our favorite stories.” To help with the discussion, they bring in experts that work at Chicago Botanic Garden to explore the science (and fiction) behind the plant references. In addition to discussing pop culture and the related science, the guests share details about the work they do at the Garden and some of the research they are working on.

In the first episode, Jasmine and Erica ask Paul CaraDonna about the drone bees featured in an episode of Black Mirror. Since many bee species are in decline, will we have to resort to employing robot bees to pollinate plants that rely on bee-assisted pollination? A great discussion about native bees and colony collapse disorder ensues.

(But maybe the idea of autonomous drone insects isn’t too far-fetched…)

In episode two, the hosts ask why humans are so obsessed with corpse flowers. Thousands of people flock to botanical gardens to see these humongous, stinky flowers on the rare occasions they are in bloom, so what is so appealing about Amorphophallus titanum? Patti Vitt joins the discussion to share details about this fascinating plant.

A corpse flower in bloom is a brief and uncommon occurrence, reminiscent of the Sumatran Century Flower in The Simpsons and the 40 Year Orchid in Dennis the Menace.

 

The third episode features the sarlaccs of Star Wars. It turns out, sarlaccs are carnivorous plants. This discovery spawns an interesting discussion with horticulturist Tom Weaver about what defines a carnivorous plant and the various ways that different carnivorous plant species capture and kill their prey.

The fourth (and latest) episode is an exploration into the magical world of mushrooms. In Alice in Wonderland, Alice encounters a large, hookah-smoking caterpillar sitting atop a giant mushroom. Are there mushrooms big enough that a person could actually sit on them like Alice does? Greg Mueller joins the podcast to address this and many other mycology-based questions. The conversation includes a great discussion about why a botanical garden (whose main focus is plants) would be interested in fungus.

The discussions in this podcast are fun and enlightening. The hosts shine the spotlight on often overlooked characters in popular media, and with the help of their guests, lead captivating conversations about the science related to these characters. With only a handful of episodes available so far, it will be easy to get caught up. And then you, like me, will find yourself anxiously looking forward to embarking on another Botanical Mystery Tour.

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Is there a plant-themed podcast or podcast episode you would like to recommend? Please do so in the comment section below.

Seed Oddities: Vivipary

Seeds house and protect infant plants. When released from their parent plant, they commence a journey that, if successful, will bring them to a suitable location where they can take up residence (upon germination) and carry out a life similar to that of their parents. Their seed coats (and often – in the case of angiosperms – the fruits they were born in) help direct them and protect them in this journey. Physical and chemical factors inhibit them from germinating prematurely – a phenomenon known as dormancy. Agents of dispersal and mechanisms of dormancy allow seeds to travel through time and space — promises of new plants yet to be realized.

There is rarely a need for a seed to germinate immediately upon reaching maturity. In many cases, such as in temperate climates or in times of drought or low light, germinating too soon could be detrimental. The most vulnerable time in a plant’s life comes when it is a young seedling. Thus, finding the right time and space to get a good start is imperative.

The fruits (and accompanying seeds) of doubleclaw (Proboscidea parviflora) are well equipped for long distance dispersal. (via wikimedia commons)

In rare instances, dispersal via seeds offers little advantage; instead, dispersal of live seedlings or propagules is preferable. For this select group of plants, vivipary is part of the reproductive strategy. In vivipary, seeds lack dormancy. Rather than waiting to be dispersed before germinating, viviparous seeds germinate inside of fruits that are still attached to their parent plants.

Occasionally, seeds are observed germinating inside tomatoes, citrus, squash, and other fruits; however, these fruits are usually overripe and often detached from the plant. In these instances, what is referred to as “vivipary” is not a genetic predisposition or part of the reproductive strategy. It’s just happenstance – a fun anomaly. The type of vivipary discussed in this post is actually quite rare, occurring in only a handful of species and prevalent in a select number of environments.

There are three main types of vivipary: true vivipary, cryptovivipary, and pseudovivipary. In true vivipary, a seed germinates inside the fruit and pushes through the fruit wall before the fruit is released. In cryptovivipary, a seed germinates inside the fruit but remains inside until after the fruit drops or splits open. Pseudovivipary is the production of bulbils or plantlets in the flower head. It does not involve seeds and is, instead, a form of asexual reproduction that will be discussed in a future post.

True vivipary is commonly seen among plant communities located in shallow, marine habitats in tropical or subtropical regions, such as mangroves or seagrasses. The term mangrove is used generally to describe a community of plants found in coastal areas growing in saline or brackish water. It also refers more specifically to the small trees and shrubs found in such environments. While not all mangrove species are viviparous, many of them are.

Seedlings of viviparous mangrove species emerge from the fruit and drop from the plant into the salty water below. From there they have the potential to float long or short distances before taking root. They may land in the soil upright, but often, as the tide recedes, they find themselves lying horizontally on the soil. Luckily, they have the remarkable ability to take root and quickly stand themselves up. Doing this allows young plants to keep their “heads” above water as the tides return. It also helps protect the shoot tips from herbivory.

Viviparous seedlings emerging from the fruits of red mangrove (Rhizophora mangle) via wikimedia commons

Another example of vivipary is found in the epiphytic cactus (and close relative of tan hua), Epiphyllum phyllanthus. Commonly known as climbing cactus, this species was studied by researchers in Brazil who harvested fruits at various stages to observe the development of the viviparous seedlings. They then planted the seedlings on three different substrates to evaluate their survival and establishment.

Epiphyllum phyllanthus is cryptoviviparous, so the germinated seeds don’t leave the fruit until after it splits open. In a sense, the mother plant is caring for her offspring before sending them out into the world. The researchers see this as “a form of parental care with subsequent conspecific [belonging to the same species] nursing.” Since the plant is epiphytic – meaning that it grows on the surface of another plant rather than in the soil – local dispersal is important, since there is no guarantee that seeds or propagules dispersed away from the host plant will find another suitable site. That being said, the researchers believe that “vivipary involves adaptation to local dispersal,” since “the greater the dispersal distance is, the higher the risk and the lower the probability of optimal dispersion.”

Epiphyllum phyllanthus via Useful Tropical Plants

While some viviparous seedlings of mangroves can travel long distances from their parent plant and don’t always root into the ground immediately, they maintain their advantage over seeds because they can root in quickly upon reaching a suitable site and lift themselves up above rising tide waters. As the authors of the Epiphyllum study put it, vivipary is “a reproductive advantage that, in addition to allowing propagules to root and grow almost immediately, favors quick establishment whenever seedlings land on suitable substrates.”

There is still much to learn about this unusual and rare botanical feature. The research that does exist is relatively scant, so it will be interesting to see what more we can discover. For now, check out the following resources:

Also, check out this You Tube video of :

Seed Oddities: Apomixis and Polyembryony

Plants have uncanny ways of reproducing themselves that are unparalleled by most other living things. Offshoots of themselves can be made by sending out modified stems above or beneath the ground which develop roots and shoots (new plants) at various points along the way. Various other underground stem and root structures can also give rise to new plants. Small sections of root, stem, or leaf can, under the right conditions, push out new plantlets in a fashion that seems otherworldly. (Picture chopping off a bit of your finger and growing a whole new you from it.)

These are some of the ways in which plants reproduce asexually, and it’s kind of freaky if you think about it. Plants can clone themselves. But one major disadvantage of reproducing this way is that clonal offspring are genetically identical to the parent plant, which truncates any advantage that might be gained by genetic mixing between two separate plants. For one, it means that a plant population composed of all clones is at risk of being wiped out if something in the environment comes along (such as a disease or change in climate) and none of the plants in the population have adapted any sort of resistance to it.

New plants forming along the lateral stems of Ranunculus flammula – via wikimedia commons

That’s where seeds come in. Seeds are produced sexually, when the gametes of one plant fuse with the gametes of another. Genetic recombination occurs, and a genetically unique individual is born, housed within a seed. Unless, of course, that seed is produced asexually. Then the seed is a clone, and we’re back to where we started.

Apomixis is the process by which seeds are produced asexually. In flowering plants, this means that viable seeds are formed even when flowers haven’t been pollinated. In some cases, pollination stimulates apomixis or is required to produce endosperm; but either way, the result is the same: an embryo containing an exact copy of the genes of its single parent plant.

To understand this process, it’s important to familiarize yourself with the basic anatomy of an ovule, the part of a plant where embryos are formed and which ultimately becomes a seed. In gymnosperms, ovules sit inside cones; in angiosperms, they are surrounded by an ovary. The wall of the ovule is called an integument. A small opening at the top of the ovule, known as a micropyle, is where the pollen tube enters. Diploid cells of the nucellus compose the interior of the ovule, and within the nucellus resides the megasporocyte, which is where meiosis occurs and egg cells are produced. In sexual reproduction, a germ cell introduced through the pollen tube fuses with the egg cell to form a zygote and eventually an embryo. In the case of apomixis, the fusion of germ cells isn’t necessary for an embryo to form.

ovule anatomy via wikimedia commons

There are three main types of apomixis: diplospory, apospory, and adventitious embryony. In diplospory, the megasporocyte skips meiosis and produces diploid cells instead of haploid cells (germ cells). These unreduced cells go on to form an embryo inside of the embryo sac, just like an egg cell would if it had been fertilized with a pollen cell. Additional unreduced cells go on to form endosperm, and the ovule then matures into a seed. This type of apomixis is common in dandelions (Taraxacum officinale). As much as bees love visiting dandelion flowers, their pollination services are not required for the production of viable seeds. Yet another reason you are stuck with dandelions in your yard whether you like it or not.

In apospory, an embryo develops inside of an embryo sac that has been formed from cells in the nucellus. Embryo development within the megasporocyte is bypassed; however, pollination is usually necessary for endosperm to form. Plant species in the grass family commonly produce seeds using this type of apomixis.

Adventitous embryony is also known as sporophytic apomixis because an embryo is formed outside of an embryo sac. Cells from either the integument or the nucellus produce an embryo vegetatively. In this case, a sexually produced embryo can form along with several vegetatively produced embryos. Extra embryos die off and a single, surviving embryo is left inside the mature seed. But not always. Two or more embryos occasionally survive, including the sexually produced one. The mature seed then consists of multiple embryos. This phenomenon is called polyembryony and is common in citrus and mangoes. When it comes to plant breeding, polyembryony is incredibly useful because the asexually derived seedlings are exact copies of their parent, which means the desirable traits of a specific cultivar are retained.

Depiction of seed with three viable embryos after germination.

Polyembryony can occur in a number of ways, and not always as a result of apomixis. In some species, additional embryos “bud off” from the sexually produced embryo. This is called cleavage polyembryony and is known to happen frequently in the pine family (Pinaceae), as well as other plant families. Another common form of polyembryony in gymnosperms is simple polyembryony, in which several egg cells in a single ovule are fertilized resulting in the development of multiple embryos. This doesn’t always mean there will be multiple seedlings sprouting from a single seed. Most embryos usually fail to mature, and only one prevails. However, sometimes more than one survives, and if you’re lucky, you’ll find a seed with multiple plant babies pushing out from the seed coat.

Up Next: Vivipary!