Pollen 101

Did you have a flashback to science class when you saw Spike, the titan arum? I sure did.

PHOTO: Tim Pollak and Dr. Shannon Still point out plant parts of the titan arum to the gathered crowd of visitors.
With Spike’s frilly spathe removed, Tim Pollak and Dr. Shannon Still had a rare opportunity to show the crowd the titan arum’s beautiful and astonishing inner plant parts.

At my not-really-science-minded high school, botany (the study of plants) was taught as a subsection of biology (the study of all life) class. During the botany rotation, we learned a bit about plant names and plant parts, sprouted a few seeds, and dissected a plant. That was about it for my formal plant-science education.

PHOTO: A young girl sniffs the titan arum's removed spathe.
Hands-on plant science at the Garden: a young visitor gets a whiff of Spike’s removed spathe, looking for that telltale stench.

Flash forward a couple of decades and, despite now being an avid gardener, I found myself struggling to keep up with the scientists who were looking deep into Spike’s structures and processes. By the time Dr. Shannon Still and floriculturist Tim Pollak removed the spathe (the frilly bract that never opened) from Spike’s spadix (the flower tower that grew to 6 feet tall), I’d had to learn all about the titan arum’s morphology (see below) and crack open books and laptops to review the basics about male and female flowers.

And then they started talking pollen.

Flashback: What is pollen?

PHOTO: Closeup of pollen emerging from male Amorphophallus titanum flowers.
Tiny squiggles of pollen emerge from the male flowers about three days after Spike’s spathe was removed.

Think of a grain of pollen as a tiny packet of one plant’s genetic material that needs to meet up with another flower’s female genetic material. Technically, pollen is a haploid or gamete, the cell that carries the male half of the plant’s chromosomes.

The covering of a pollen grain is directly related to how the pollen travels to the next flower. That’s why wind-pollinated plants like sweet corn or oak trees have pollen as dry and fine as dust (indeed, the word “pollen” derives from the Latin for fine flour or dust). Orchids have developed waxy balls of pollen (pollinia) that stick to the heads and bodies of the many insects, hummingbirds, and mammals they use as pollinators. And, notoriously, the pollen of ragweed is a tiny spike—the better to hold on to moist spots like the inside of human nasal passages, where the grains never germinate, but cause all sorts of sneezing and snuffling.

Honeybee-pollinated plants (like many fruits, nuts, and vegetables) have evolved along with the bees themselves, offering up both nectar and pollen as food in exchange for the movement of pollen from plant to plant.

Flashback: Why are insects pollinators?

In a word, efficiency. Plants that rely on the wind are at the mercy of the wind: much of the pollen is wasted, as it never lands anywhere near a female flower’s stigma. Ditto for plants that rely on water. Insects are much more reliable, traveling directly from one flower to another, greatly increasing the chance of pollination. Bees are especially reliable, as they prefer to work an entire plant or crop of the same flower rather than skipping from one kind of flower to another. (That’s why attentive beekeepers can get a harvest of “pure” clover or linden blossom honey, rather than a wildflower mix.)

In nature, Spike’s pollinators are carrion beetles and dung flies—insects that would be attracted by the titan arum’s rotten smell and nighttime bloom.

Flashback: How does pollen work?

PHOTO: A single female flower from titan arum Spike lies in Dr. Shannon Still's hand.
Dr. Shannon Still shows the crowd gathered around Spike one of the titan arum’s female flowers .

When a grain of pollen lands in the right place—the tip of the female flower’s reproductive structure, called the stigma—the pollen grain chemically tests the landing ground via proteins that signal genetic compatibility…or not. If deemed to be a good place to germinate, the pollen grain sends a rootlike sprout down into the style (the tube with the stigma on top), eventually reaching all the way down inside the ovary and ovule…where the male chromosomes and female chromosomes meet for fertilization and seed development.

Flash forward: What’s next for Spike?

Spike’s pollen never got the chance to hitch a ride on a carrion beetle’s back to the next titan arum in the rainforest. That’s why “Titan Tim” Pollak collected the pollen when it developed a couple of days after Spike’s operation.

Pollak says that they didn’t collect much of the bright yellow, talc-like powder—just a few test tubes’ worth (further proof that Spike ran out of energy). The pollen will be mixed with powdered milk—yes, powdered milk—in order to absorb moisture and separate the grains. Next, it will be frozen at minus 20 degrees Fahrenheit and stored in the freezer at the Garden’s seed bank.

PHOTO: As the spadix collapses from age, horticulturist Tim Pollak harvests the pollen from Spike's male flowers.
As the spadix collapses from age, horticulturist Tim Pollak harvests the pollen from Spike’s male flowers.

Spike’s pollen could then be shared with other botanical gardens or arboreta that would like to pollinate their blooming titan arums. The American Public Gardens Association has a listserve that shares notice of pollen needed or available; the Chicago Botanic Garden is a contributing member. By sharing Spike’s pollen, the hope is to increase diversity among the rare flowers blooming outside of Sumatra, the titan’s native habitat.

Pollen means that Spike lives on! Can’t wait for the next titan arum to bloom (we have seven more besides Spike in our production area)…and for the next plant flashback.

So you want to be a plant scientist?

PHOTO: Amorphophallus titanum pollen in a test tube.
An Amorphophallus titanum pollen sample is ready to be stored for future pollination.

The science of botany runs deep; at our Daniel F. and Ada L. Rice Plant Conservation Science Center, you can see scientists in many of the fields below in action. Got a STEM-minded kid? Perhaps he or she would like to study this list, which was compiled by Boyce Tankersley, director of living plant documentation, in response to the question, “What is the study of flowers called?”

  • Botany is the study of plants.
  • Arboriculture is the study of trees.
  • BioInformatics is the art and science of recording biological information.
  • Cellular biology is the study of cell constituents.
  • Floristics refers to the geographic distribution of plants.
  • Genetics is the study of gene interactions.
  • Horticulture is the art and science of growing plants.
  • Nomenclature is the naming of plants.
  • Paleobotany searches out and examines plant fossils.
  • Plant breeding does what it says.
  • Plant morphology is the study of plant structures.
  • Plant pathology studies plant pathogens and plant interactions.
  • Plant physiology is the study of plant functions such as photosynthesis.
  • Palynology studies both living and fossilized pollen and spores.
  • Taxonomy studies the relationship of one plant to other plants.

©2015 Chicago Botanic Garden and my.chicagobotanic.org

Spike’s Teachable Moment

What an amazing plant science moment occurred in the Semitropical Greenhouse this morning, as a fascinated crowd gathered to see what was happening with Spike, the titan arum.

On Saturday, it was determined that Spike had run out of the energy it needed to continue its bloom cycle. Spike is powered by energy from the sun, stored in its beach-ball-sized corm—a tuber-like underground structure. A tremendous amount of energy goes into producing the single, giant flower structure that a titan can send up in its first decade or so of life (Spike is about 12 years old).

Overheard: “I wish my biology teacher was here.”

As this week’s expected bloom time passed, our science and horticultural staff went into action. Spike wasn’t dying—but the flower structure had stopped maturing, and the spathe did not open. On Friday, Dr. Shannon Still, conservation scientist, and Tim Pollak, the floriculturist who had raised Spike from a seed, peeked inside the frilly spathe to check for pollen.

“If there had been pollen, it would have been all over my hand,” Still said. Pollen’s absence meant that the male and female flowers might not be fully developed. The possibility remained that pollen might still develop, even though the spathe would not open—and THAT led to the decision to remove the “frozen” spathe to see what was happening with the real flowers inside.

Overheard: “We were watching it every day. Every 20 minutes or so.”

First, Still assembled a working kit: scalpel, probes, test tubes, paintbrushes and a “scoopula” (to collect pollen).

At 10 a.m. today, staff gathered for the delicate procedure. Pollak and Still fist bumped…and the operation began. 

As Still began cutting just above the peduncle (stalk), the crowd grew quiet. Dr. Pat Herendeen, senior director, Systematics and Evolutionary Biology, narrated for the crowd. As the spathe started to come away from the towering spadix, the internal color started to be visible.

Left: a cross-section of the spathe reveals the cell structure inside. Right: close-up on the hundreds of male (top) and female (bottom) flowers inside Spike's spathe.
Left: A cross-section of the spathe reveals the cell structure inside. Right: A close-up of the hundreds of male (top) and female (bottom) flowers inside Spike’s spathe.

“The spathe feels a bit like cabbage leaves, with a rubbery texture,” Herendeen said. “The color inside varies from one plant to another in nature. It is dark maroon, the color of rotting meat, which is meant to attract the flies and beetles that are the plant’s natural pollinators.”

Pollak held the spathe steady as Still continued to free it from the stalk. With one last cut, it came free—and the crowd gasped as the inside of the spathe was unfurled and the true flowers at the base of the spadix were revealed—pale rows of bumpy-looking male flowers atop a strip of orange and brown female flowers.

Tim Pollak and Shannon Still make the first cut.
Left: Tim Pollak and Shannon Still make the first cut. Right: Tim Pollak reveals the spathe’s ravishing color.

Herendeen answered as questions flew: The male flowers do not appear to have produced pollen yet. Spike’s fabled scent is only detectable very close up to the spathe—much less apparent than it was earlier in the week.

Cameras focused in on the flower structure, as Still and Pollak carried the two large pieces of the cut-away spathe over to the crowd. Hands reached out for a touch; noses leaned in for a sniff. Spike’s spathe was set out on a gallery table so that everyone could touch and admire it before it begins to wilt.

Overheard: “Spike was the topic of dinner conversation with our two sons every night for the past week.”

While television camera crews stepped in for close-ups on the plant’s flowers, interviewers questioned the scientists: Where does the scent come from? (It’s believed that the tall appendix helps produce the scent, though scientists are also investigating the female flowers themselves.) Would Spike bloom again? (Probably, but the corm would have to recover first, by sending up an annual leaf for a few years to gather more energy.)

Cross-legged on the floor opposite Spike sat Chicago artist Heeyoung Kim, who sketched intently during the entire process. Her intricate pencil markings captured Spike’s pleats and tightly clustered flowers—the beginnings of a botanical illustration that could inform future scientists studying the titan arum’s beautiful structure for years to come.

We have been so thrilled with the intensity of interest in Spike—it’s not every day that crowds gather to watch a plant grow! We’ll continue to keep you posted about possible pollen development, our scientists’ thoughts about Spike’s arrested development, and on the progress of the eight other titan arums now growing in our production greenhouses. 

Left: what a great vibe! Right: Kris Jarantoski explains Spike's spathe to a young visitor.
Left: What a great vibe from the gathered crowd! Right: Kris Jarantoski, executive vice president and director, explains Spike’s spathe to a young visitor.

For more information please visit our titan arum page.

©2015 Chicago Botanic Garden and my.chicagobotanic.org

Can Spike’s “Perfume” Be Captured in a Jar?

Of the many Spike-related questions asked by visitors this week, our favorite came from 8-year-old Prairie! In the video below, Prairie wants to know, in essence, if she can transport Spike’s malodorous odor from the Chicago Botanic Garden to her classroom.

Good question, Prairie!

Conservation scientist Dr. Shannon Still has a fascinating response. Dr. Still will attempt to pollinate Spike’s flowers during bloom with pollen shared by our friends from The Huntington Library, Art Collections, and Botanical Gardens, and Denver Botanic Gardens.

Prairie, your experiment with scent would make a great science project! If you come to the Garden on the night Spike blooms, perhaps you’ll get to see Shannon Still working on “Operation Pollination.” Introduce yourself if you’re there!


©2015 Chicago Botanic Garden and my.chicagobotanic.org

Care and Feeding for a Giant Bloom

One of the top questions we have been getting about Spike the titan arum is “How do you know how much water to give him?” 

PHOTO: Titan arum (Amorphophallus titanum) a mere few days from bloom.
It’s nearly showtime! The outer bracts have fallen away, and the spathe is now showing a slight purple cast.

The care and feeding that we have given Spike and his fellow titan arums—our collection of nine Amorphophallus titanum growing in our production greenhouses—is very specific!

Yes, the cultivation requirements for these plants are strict. Titan arums require well-maintained conditions of high humidity and high temperature—similar to their natural conditions in the tropical rainforests of Sumatra. Therefore, the cultivation is not particularly suitable for most beginners or homeowners with minimal greenhouse facilities.

Watering the bloom

During Spike’s flowering stage, we make sure the soil is evenly moist at all times. This is important to continue flower development and prevent the spathe (the frilly modified leaf) from drying out or not opening. We also pay special attention to air humidity—we try to keep the humidity between 75 to 90 percent saturation at all times. How? We keep the floors wet and prevent excessive venting in the greenhouse.

PHOTO: A hygrometer in Spike's planter measures relative humidity in the greenhouse.
A hygrometer in Spike’s planter measures relative humidity in the greenhouse.

Watering for leaf growth

Spike and the rest of the collection have grown through many leaf and dormancy cycles into larger corms (a type of underground tuber or bulb). It would seem that tending the growing corms would be about as complicated as a typical bulb, but a close eye must be kept on how the corms are watered to prevent them from drying out or rotting. As the leaves grow larger each growth period (12 to 18 months), their increasingly larger corms may prevent the soil beneath them from becoming wet. Increasing watering to make sure the soil is kept moist at the bottom of the tuber could cause the corm to rot, as most of its roots develop on the upper surface. The growing medium must be evenly moist at all times, but not wet, and the soil should never dry out completely, especially at the start of leaf development. Using a loose medium and a layer of gravel drainage in the planters ensures that water reaches all parts of the corm without flooding it. Finally, we repot the corms—a lot—to make sure the soil stays evenly moist, and to give them room to grow! 

Yes, we went through a lot of pots…

PHOTO: An Amorphophallus titanum corm.
When repotting very large corms, it is important not to lay them directly on a hard surface. Their own weight can cause damage to the bottom of the corm and cause rotting. Photo by Georgialh (Own work) [CC BY-SA 4.0], via Wikimedia Commons.

Spike was repotted many times as the corm continued to grow larger each season. In fact, several times the pots or containers that the plant was growing in would crack or break as the swelling corm beneath the soil surface would “push” outward and damage its container. Last fall, we finally had our carpenters here at the Chicago Botanic Garden make big 42″-by- 42″ wooden crates as a more permanent home to grow Spike and several others in our collection. At the end of each dormancy cycle, we carefully lift the corms, inspect them for pests or rot, and remove any unwanted new bulbils that may have formed. When moving these corms to their new homes, we provided extra drainage at the bottom of the crates by amending the soil with more perlite at the bottom and a layer of gravel.

How hot is it in here, exactly?

Not surprisingly for a Sumatran plant, Amorphophallus titanum prefer to be grown at temperatures between 70 to 85 degrees Fahrenheit during the day and 68 to 80 degrees at night—pretty warm, and without a lot of temperature fluctuation. Temperatures above 90 degrees or extreme cool temperatures may damage the foliage or flower, so we are keeping a close eye on Spike as visitors come to check on his progress.

The future’s so bright…

Spike also needs a lot of sunlight—both in leaf and flower form. We provide minimal shading to our collection (enough to prevent foliar damage), and only during the hottest summer months. Does that mean we need additional lighting to compensate for Chicago being so far north of the equator? Actually, no. No additional lighting or day length control have been necessary. The lights currently surrounding Spike in the greenhouse are for our time-lapse cameras, to make sure our star is lit evenly on his performance night!

Does Spike need a lot of fertilizer?

Definitely! Titan arums require high levels of fertilizer to be applied on a regular basis while in the leaf stage. We fertilized at every other watering, especially during the summer months, and reduced fertilization during the colder winter months. When we determined the emerging shoot of Spike was indeed a flower, however, fertilization ceased.

Are you sure you don’t know exactly when Spike will open?

We’re sure we don’t know for certain. We have key factors we look for, like the bracts (outer leaves) shriveling up and falling away 48 hours before a bloom. But this is not always the rule—in some cases, blooming is what makes the bracts finally fall away from the flower! In the end, only Spike knows when he’ll bloom.

PHOTO: Spike the titan arum on display at the Chicago Botanic Garden.
Spike’s fans check in in his progress—it won’t be long, now!

As you can see, the cultivation of our Amorphophallus titanum collection can be somewhat challenging! Providing them with the unique cultural requirements to get them to live long enough and to eventually bloom is a mighty task. However, all the extra “TLC” given by our greenhouse staff will be well worth the long wait to see Spike bloom in just a few days.


©2015 Chicago Botanic Garden and my.chicagobotanic.org

About That Smell…

The night Spike blooms will thrill us all in the semi-tropical greenhouse, with its breathtaking flower…accompanied by a titanically rotten smell. 

“Your heart is full of unwashed socks, your soul is full of gunk, Mr. Grinch. The three words that best describe you are as follows— and I quote: stink, stank, stunk!”
—Dr. Seuss

“Titan Tim” Pollak here once again, with an update on Spike, our still-growing titan arum. Spike continues to get bigger, not only in height, but also in girth! What we’re really curious about, however, is the aroma.

The stench is one of the cool reasons to stay up late and come to the Garden that night—we’ll be open from 9 p.m. to 2 a.m.

Here’s what to expect in terms of scent:

What an "arum-atic" combination of scents!
What an “arum-atic” combination of scents!
  • As the spathe gradually unfurls, the spadix releases powerful odors meant to attract pollinators. The potency of the aroma gradually increases from late evening until the middle of the night and then tapers off as morning arrives.
  • Analyses of chemicals released by the spadix show the “stench” includes dimethyl trisulfide (like limburger cheese), dimethyl disulfide, trimethylamine (rotting fish), isovaleric acid (sweaty socks), benzyl alcohol (sweet floral scent), phenol (like Chloraseptic), and indole (like mothballs).
  • The titan arum’s odor has been described in many other terms as well: rotting flesh, rancid meat, rotting animal carcass, old dirty socks, and even the smell of death itself, which accounts for the plant’s common name, the corpse flower.
  • In its natural habitat on the island of Sumatra in Indonesia, the “fragrance” is used to attract the carrion-eating beetles, dung beetles, and flesh flies that pollinate the titan arum. The inflorescence’s deep red color and texture contribute to the illusion that the spathe is a piece of meat.
  • During bloom, the tip of the spadix is approximately human body temperature, which helps the fragrance volatilize (turn to vapor) and travel long distances; the heat may also advertise that there’s a fresh carcass for insects to check out. 
PHOTO: Dung beetle (Catharsius sp.)
Carrion flies and dung beetles like this one (Catharsius sp.) think that stink smells great. Photo ©2012 via potokito-myshot.blogspot.com

A different view of ewwww!

Carrion beetles, dung flies, and flesh flies aren’t responding to the call of the titan arum’s scent because they want to be pollinators—they’re responding because they want a good environment in which to lay their eggs. 

In the wild, mama beetles and flies lay eggs on dead animals or animal feces knowing that the larvae that hatch will have an immediately-available, rich source of food.

In its natural rainforest habitat, the titan arum has adapted to that fact. Over evolutionary time, it has developed the right scent to attract those insects—and, like many scented flowers, to deceive them with scent into acting as the unwitting spreaders of their pollen. 

Keep checking back for more on Spike’s progress!

©2015 Chicago Botanic Garden and my.chicagobotanic.org