March 3, 2021 by awkwardbotany

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.

via wikimedia commons; user: Redmarkviolinist

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

Additional Resources:

Morton Arboretum You Tube Channel – “The Ups and Downs of Acorn Crops: A Comparison of Mast Seeding Among Oaks”
Pearse, I.S, et al. (2016). Mechanisms of mast seeding: resources, weather, cues, and selection. New Phytologist 212: 546-562.
Appalachian Mountain Club – Mystery of the Mast Year

August 26, 2020 by awkwardbotany

Flowers Growing Out of Flowers (Things Are Getting Weird Out There)

I’m sure that anyone living through the events of 2020 would agree, these are truly wild times. So, when I stumbled across some purple coneflowers that appeared to be growing flowers out of flowers, I thought to myself, “Of course! Why not!?!” The world is upside down. Anything is possible.

As it turns out, however, this phenomenon occurs more frequently than I was aware. But it’s not necessarily a good thing, particularly if you’re concerned about plant health. We’ll get to that in a minute. First, what’s going on with these flowers?

Flowers in the aster family are unique. They have the appearance of being a single flower but are actually a cluster of two types of much smaller flowers all packed in together. Purple coneflower (Echinacea purpurea) is a great example of this. Its flower heads are composed of dozens of disc flowers surrounded by a series of ray flowers. The minuscule disc flowers form the cone-like center of the inflorescence. The petals that surround the cone are individual ray flowers. This tight cluster of many small flowers (or florets) is known as a composite. Sunflowers are another example of this type of inflorescence.

Flowers are distinct organs. Not only are they the reproductive structures of flowering plants, but unlike the rest of the plant, they exhibit determinate growth. Flowers are, after all, plant shoots that have been “told” to stop growing like other shoots and instead modify themselves into reproductive organs and other associated structures. Unlike other shoots, which continue to grow (or at least have the potential to), a flower (and the fruit it produces) is the end result for this reproductive shoot. This is what is meant by determinate growth. However, sometimes things go awry, and the modified shoots and leaves that make up a flower don’t develop as expected, producing some bizarre looking structures as a result.

An example of this is a double flower. Plants with double flowers have mutations in their genes that cause disruptions during floral development. This means that their stamens and carpels (the reproductive organs of the flowers) don’t develop properly. Instead, they become additional petals or flowers, resulting in a flower composed of petals upon petals upon petals – a look that some people like, but that have virtually nothing to offer the pollinators that typically visit them. Because of their ornamental value, double-flowered varieties of numerous species – including purple coneflower – can be found in the horticultural trade.

double-flowered purple coneflower

Genetic mutations are one way that odd looking flowers come about. It is not the cause, however, of the freak flowers that I recently came across. What I witnessed was something called phyllody and was the result of an infection most likely introduced to the plant by a leafhopper or some other sap-sucking insect. Phyllody, which has a variety of causes, is a disruption in plant hormones that leads to leaves growing in place of flower parts. As a result, the flowers become sterile and green in color. In the case of purple coneflower, leafy structures are produced atop shoots arising from the middle of ray and/or disc florets. In other species, shoots aren’t visible and instead the inflorescence is just a cluster of leaves. In a sense, the reproductive shoot has returned to indeterminate growth, having switched back to shoot and leaf production.

Phyllody can have either biotic or abiotic causes. Biotic meaning infection by plant pathogens – including certain viruses, bacteria, and fungi – or damage by insects. Abiotic factors like hot weather and lack of water can result in a temporary case of phyllody in some plants. Phyllody plus a number of other symptoms made it clear that the purple coneflower I encountered had a fairly common disease known as aster yellows. This condition is caused by a bacterial parasite called a phytoplasma, and is introduced to the plant via a sap-sucking insect. It then spreads throughout the plant, infecting all parts. The phyllody was a dead give away, but even the flowers that weren’t alien-looking were discolored. The typical vibrant purple of the ray flowers was instead a faded pink color. The flowers that had advanced phyllody – along with the rest of the plant – were turning yellow-green.

This inflorescence isn’t exhibiting phyllody yet, but the purple color in the ray flowers is quickly fading.

Hundreds of plant species are susceptible to aster yellows, and not just those in the aster family. Once a plant is infected with aster yellows, it has it for good and will never grow or reproduce properly. For this reason, it is best to remove infected plants from the garden to avoid spreading the infection to other plants. As cool as the flowers may look, infected plants just aren’t worth saving.

The Hidden Flowers of Viola

Violas keep a secret hidden below their foliage. Sometimes they even bury it shallowly in the soil near their roots. I suppose it’s not a secret really, just something out of sight. There isn’t a reason to show it off, after all. Showy flowers are showy for the sole purpose of attracting pollinators. If pollinators are unnecessary, there is no reason for showy flowers, or to even show your flowers at all. That’s the story behind the cleistogamous flowers of violas. They are a secret only because unless you know to look for them, you would have no idea they were there at all.

Cleistogamy means closed marriage, and it describes a self-pollinating flower whose petals remain sealed shut. The opposite of cleistogamy is chasmogamy (open marriage). Most of the flowers we are familiar with are chasmogamous. They open and expose their sex parts in order to allow for cross-pollination (self-pollination can also occur in such flowers). Violas have chasmogamous flowers too. They are the familiar five-petaled flowers raised up on slender stalks above the green foliage. Cross-pollination occurs in these flowers, and seed-bearing fruits are the result. Perhaps as a way to ensure reproduction, violas also produce cleistogamous flowers, buried below their leaves.

an illustration of the cleistogamous flower of Viola sylvatica opened to reveal its sex parts — via wikimedia commons

Flowers are expensive things to make, especially when the goal is to attract pollinators. Colorful petals, nectar, nutritious pollen, and other features that help advertise to potential pollinators all require significant resources. All this effort is worth it when it results in the ample production of viable seeds, but what if it doesn’t? Having a method for self-pollination ensures that reproduction will proceed in the absence of pollinators or in the event that floral visitors don’t get the job done. A downside, of course, is that a seed produced via self-pollination is essentially a clone of the parent plant. There will be no mixing of genes with other individuals. This isn’t necessarily bad, at least in the short term, but it has its downsides. A good strategy is a mixture of both cross- and self-pollination – a strategy that violas employ.

The cleistogamous flowers of violas generally appear in the summer or fall, after the chasmogamous flowers have done their thing. The fruits they form split open when mature and deposit their seeds directly below the parent plant. Some are also carried away by ants and dispersed to new locations. Seeds produced in these hidden flowers are generally superior and more abundant compared to those produced by their showy counterparts. People who find violas to be a troublesome lawn weed – expanding far and wide to the exclusion of turfgrass – have these hidden flowers to blame.

That being said, there is a defense for violas. In the book The Living Landscape by Rick Darke and Doug Tallamy, Tallamy writes: “Plants such as the common blue violet (Viola sororia), long dismissed by gardeners as a weed, can be reconstituted as desirable components of the herbaceous layer when their ecosystem functionality is re-evaluated. Violets are the sole larval food source for fritillary butterflies. Eliminating violets eliminates fritillaries, but finding ways to incorporate violets in garden design supports fritillaries.”

sweet violet (Viola odorata)

In my search for the cleistogamous flowers of viola, I dug up a sweet violet (Viola odorata). I was too late to catch it in bloom, but the product of its flowers – round, purple, fuzzy fruits – were revealed as I uprooted the plant. Some of the fruits were already opening, exposing shiny, light brown seeds with prominent, white elaiosomes, there to tempt ants into aiding in their dispersal. I may have missed getting to see what John Eastman calls “violet’s most important flowers,” but the product of these flowers was certainly worth the effort.

Fruits formed from the cleistogamous flowers of sweet violet (Viola odorata)

Up close and personal with the fruit of a cleistogamous flower

The seeds (elaiosomes included) produced by the cleistogamous flower of sweet violet (Viola odorata)

Weeds of Boise: Abandoned Pizza Hut on Ann Morrison Park Drive

There is an old Pizza Hut on the corner of Ann Morrison Park Drive and Lusk Street. I’m not sure how long it’s been closed (if someone knows for sure, please let me know), but it has to be well over a year – probably several years. It’s clear that the landscaping has not been maintained for a while. The turf grass in the hellstrips is now mostly weeds, the Callery pears and crabapples are in need of some serious pruning, and the mugo pines and horizontal junipers are slowly dying off. On the other hand, the Oregon grapes and barberries look just fine. They never really needed our help anyway.

I like checking out lots with recently abandoned buildings because you can see in real time just how quickly weeds take over once humans stop their meddling. As the months and years pass, and as the plants that humans intentionally placed there decline, it becomes increasingly obvious that weeds truly are the wild flora of our cities.

My first few visits to this site were on March 21st, 25th and 28th of 2020. During those visits, I made a list of all the weeds that I could easily identify and noted a few individuals that I will need to come back to. What follows are photos of a few of the weeds I came across, along with a list of the weeds I was able to identify.

Every lot needs a dandelion (Taraxacum officinale).

Common mallow (Malva neglecta) in mulch.

The turf grass in the hellstrips has been replaced by several different weeds including tiny, early spring favorites like bur buttercup (Ceratocephala testiculata) pictured here and spring draba (Draba verna).

Common groundsel (Senecio vulgaris) is prolific in a bed on the north side of the building. On the east side, this plant had already flowered and gone to seed by mid-March.

The tough taproot of alfalfa (Medicago sativa) easily works its way into cracks in pavement and concrete.

A bull thistle rosette (Cirsium vulgaris) perhaps?

Cheatgrass (Bromus tectorum) was common on the site, including (perhaps not surprisingly) in this parking block.

horseweed seedling (Conyza canadensis)

Weeds found at the abandoned Pizza Hut on Ann Morrison Park Drive:

Bromus tectorum (cheatgrass)
Ceratocephala testiculata (bur buttercup)
Cirsium vulgare (bull thistle)
Conyza canadensis (horseweed)
Draba verna (spring draba)
Hordeum murinum ssp. glaucum (smooth barley)
Lactuca serriola (prickly lettuce)
Malva neglecta (common mallow)
Medicago sativa (alfalfa)
Poa bulbosa (bulbous bluegrass)
Rumex crispus (curly dock)
Senecio vulgaris (common groundsel)
Taraxacum officinale (dandelion)
Ulmus pumila (Siberian elm)

This post will be updated as I identify more of the weeds and capture more photos. I also anticipate that this lot will not be abandoned for that much longer. It’s located near Boise State University in an area that has seen a lot of development in the past few years. I can’t imagine prime real estate like this will stay feral indefinitely. Until something is done with it, I’ll keep checking in.

October 24, 2018 by awkwardbotany

Field Trip: UBC Botanical Garden and VanDusen Botanical Garden

Last week, we found ourselves in Vancouver, British Columbia for a work-related conference put on by American Public Gardens Association. In addition to learning heaps about plant collections and (among other things) the record keeping involved in maintaining such collections, we got a chance to visit two Vancouver botanical gardens. Both gardens were pretty big, so covering the entire area in the pace we generally like to go in the time that was allotted was simply not possible. Still, we were smitten by what we were able to see and would happily return given the chance. What follows are a few photos from each of the gardens.

UBC Botanical Garden

UBC Botanical Garden is located at the University of British Columbia. Established in 1916, it is Canada’s oldest university botanical garden. We saw a small fraction of the Asian Garden, which is expansive, and instead spent most of our time in other areas, including the Alpine Garden, the Carolinian Forest Garden, the Food Garden, and one of my favorite spots, the BC Rainforest Garden. The Rainforest Garden is a collection of plants native to British Columbia, which was the original focus of UBC Botanical Garden’s first director, John Davidson.

fall foliage of redvein enkianthus (Enkianthus campanulatus)

Franklin tree in bloom (Franklinia alatamaha) in the Carolinian Forest Garden

alpine troughs

bellflower smartweed (Aconogonon campanulatum)

cutleaf smooth sumac (Rhus glabra ‘Laciniata’) in the BC Rainforest Garden

the fruits of Gaultheria pumila in the E.H. Lohbrunner Alpine Garden

Himalayan blueberry (Vaccinium moupinense) in the E.H. Lohbrunner Alpine Garden

VanDusen Botanical Garden

VanDusen Botanical Garden is a 55 acre garden that opened in 1975 and is located on land that was once a golf course. It features an extensive collection of plants from around the world accompanied by a series of lakes and ponds as well as lots of other interesting features (like a Scottish Shelter, a Korean Pavilion, an Elizabethan Maze, and more). Our time there was far too brief. The whirlwind tour we joined, led by the education director, was a lot of fun, and if the threat of missing our bus wasn’t looming, we would have been happy to stay much longer.

Japanese anemone (Anemone x hybrida ‘Whirlwind’)

fall color on the shore of Heron Lake

knees of bald cypress (Taxodium distichum) in R. Roy Forster Cypress Pond

witch hazel (Hamamelis x intermedia ‘Pallida’)

a grove of giant redwoods (Sequoiadendron giganteum)

We tried the fruit of dead man’s fingers (Decaisnea insignis). It tastes a bit like watermelon.

Japanese stewartia (Stewartia pseudocamellia)

More Awkward Botany Field Trips:

October 10, 2018 by awkwardbotany

Botany in Popular Culture: The Tan Hua Flowers in Crazy Rich Asians

When a flower blooms, a celebration is in order. Flowers abound for much of the year, which means parties are called for pretty much non-stop (something Andrew W.K. would surely endorse). Since we can’t possibly celebrate every bloom, there are certain plants we have decided to pay more attention to – plants whose flowers aren’t so prolific, predictable, or long-lived; or plants whose flowers come infrequently or at odd times of the day (or night).

This is the case with the flowers of the night blooming cactus, Epiphyllum oxypetalum, which goes by many names including Dutchman’s pipe cactus, queen of the night, orchid cactus, night blooming cereus, and tan hua. Tan hua is the Chinese name for the plant, and this is how it is referred to in the book, Crazy Rich Asians by Kevin Kwan.

In the book, Nick Young brings his American girlfriend, Rachel Chu, to meet his ridiculously wealthy family in Singapore. Before the trip, Rachel was in the dark about the Young’s wealth. She first meets the family and their gargantuan mansion when Nick’s grandma, seeing that her tan hua flowers are about to bloom, throws an impromptu (and lavish) party. Nick refers to the flowers as “very rare,” blooming “extremely infrequently,” and “quite something to witness.”

In a seperate conversation, Nick’s cousin, Astrid, tries to convince her husband to attend the party by claiming, “it’s awfully good luck to see the flowers bloom.” Later, another one of Nick’s cousins tells Rachel, “it’s considered to be very auspicious to witness tan huas blooming.”

Tan hua (Epiphyllum oxypetalum) via wikimedia commons

Native to Mexico and Guatemala, E. oxypetalum was first brought to China in the 1600’s. Its beauty and intrigue along with its relative ease of cultivation helped it become popular and widespread across Asia and other parts of the world. Watching it bloom is considered a sacred experience by many, including in India, where it is said to bring luck and prosperity to households who are fortunate enough to see theirs bloom.

Epiphyllums are epiphytic, meaning they grow non-parasitically on the surfaces of other plants, such as in the crevices of bark or the crotches of branches. Like other cacti, they are essentially leafless, but their stems are broad, flat, and leaf-like in appearance. Showy, fragrant flowers are born along the margins of stems. The flowers of tan hua, as described in Crazy Rich Asians, appear as “pale reddish petals curled tightly like delicate fingers grasping a silken white peach.” A report (accompanied by photos) published by Sacred Heart University describes watching tan hua flowers progess from bud formation to full bloom, a process that took more than two weeks.

via wikimedia commons

Tan huas are certainly not rare, as Nick described them. A number of Epiphyllum species and their hybrids are commonly cultivated; there is even an Epiphyllum Trail at San Diego Zoo’s Safari Park. Listed as “least concern” on the IUCN Red List, their popularity as ornamentals is noted but is not seen as affecting wild populations. Night blooming plants, while fascinating, aren’t all that rare either. Such plants have adapted relationships with creatures, like bats and moths, that are active during the night, employing their assistance with pollination. A paper published in Plant Systematics and Evolution describes the floral characteristics of Epiphyllum and similar genera: “The hawkmoth-flower syndrome, consisting of strongly-scented, night-blooming flowers with white or whitish perianths and long slender nectar-containing floral tubes is present in Cereus, Trichocereus, Selenicereus, Discocactus, Epiphyllum, and a number of other cactus genera.”

That being said, the specialness of a short-lived, infrequent, night blooming flower should not be understated, and really, parties being thrown in honor of any plant are something I can certainly get behind. Sitting in the courtyard late at night, the Young family and their guests watched as “the tightly rolled petals of the tan huas unfurled like a slow-motion movie to reveal a profusion of feathery white petals that kept expanding into an explosive sunburst pattern.” The look of it reminds Astrid of “a swan ruffling its wings, about to take flight.”

Later, “the tan huas began to wilt just as swiftly and mysteriously as they had bloomed, filling the night air with an intoxicating scent as they shriveled into spent lifeless petals.”

via wikimedia commons

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