Stop and Smell the Anthuriums

Instead of stopping to smell the roses, maybe it’s time to appreciate the aroma of anthuriums.

Anthurium is a genus of plants in the aroid family, Araceae. You’ve probably seen one before, and may even have one in your house. Commercially available Anthurium are often sold as houseplants—noted for their colorful spathe, long-lasting bloom, and waxy appearance. Some are even mistaken for artificial plants because of those characteristics, and also because these household varieties generally don’t produce any noticeable scent.

More than likely, the Anthurium you’ve come across commercially were one of a small handful of species or hybrids, with A. andraeanum being the most common. But there are more than one thousand species found in the wild. Unlike most of its scentless cultivated cousins, some wild Anthurium deploy a bouquet of fragrances.

Scent is a powerful plant tool for attracting pollinators. Much has been made about the scent of one particularly infamous aroid, the corpse flower. Along with some of its stinky cousins, Amorphophallus titanum is well known for the unpleasant odor that gives it its common name. The foul scent of the corpse flower is designed to attract pollinators—in its case, beetles and carrion flies.

Follow Your Nose

Monica Carlsen is one of the Missouri Botanical Garden’s aroid experts, who specializes in Anthurium research. Through a grant from the Living Earth Collaborative, she is investigating the role scents play in plant/pollinator interactions in Anthurium. In October 2019, Carlsen teamed up with researchers Florian Etl and Corinna Ehn from the University of Vienna, Austria, to capture the scents of Anthurium blooming in the Garden’s aroid greenhouses.

Collecting the scent is fairly simple. Start by following your nose. Anthurium scents can run the spectrum from sweet like marzipan, mango, and blueberry—to more unpleasant smells like old shoes, wet dog, even vomit. While the human perception of these scents is important, smell can be subjective. Some plant scents may even be too subtle for human noses to notice. To get to the heart of what gives a specific species its aroma, you need to dig a little deeper.

After sniffing out a particularly fragrant inflorescence, the researchers covered the spadix with a plastic bag to let the scent accumulate. Then a special carbon filament attached to an air pump captures the scent for analysis.

By using the living collection in the Garden’s greenhouse, these researchers were able to collect scent samples from 90 species of Anthurium. That amount of data would have taken years of field work to collect from wild sources, even bordering on an impossible task. “It’s like paradise for us,” says Etl.

Even with such a resource available, it still took two weeks of sampling and some odd hours. Certain species only release their scent late at night, while others only produce smells in the early morning or mid afternoon.

Carlsen will continue sampling Anthurium scents in the Garden greenhouses, using the techniques she learned from Etl and Ehn. Students interested in assisting with this work can contact her directly for more information.

What’s That Smell?

The scent samples collected in St. Louis will be sent to the University of Salzburg, Austria, for analysis using a machine called a gas chromatograph. It can isolate each chemical compound and determine which are responsible for certain smells.

By capturing control samples of the ambient air in the greenhouse, Etl and Ehn can further refine which particular compounds are actually coming from the flowers sampled and which are not.

For example, you would likely find the chemical limonene in the scent of Anthurium ochranthum, which smells a bit like lemon. That same chemical is also used to provide the citrusy smell in lemon-scented cleaning products. Compounds like pinene (pine-scented) and eugenol (a clove-like scent) are also found in the scent profiles of certain Anthurium.

The scent data will be combined with DNA samples, pollen samples, and herbarium specimens to build a more complete picture of each Anthurium studied for this project.

Anthurium ochranthum in the Missouri Botanical Garden aroid greenhouses. Photo by Cassidy Moody.

Fragrant Field Work

The work will eventually extend far beyond the Garden walls. In 2020, Carlsen and researchers from St. Louis University, University of Missouri-St. Louis, and the St. Louis Zoo, will travel to Colombia to collect field data. In the forests where they’ll be working, it’s common to find multiple species of Anthurium all competing for the attention of pollinators.

The team will collect scents and observe the insects that visit certain species of Anthurium, hoping to determine if floral fragrance plays a role in specific pollinator interactions. For instance, Anthurium acutifolium is visited by male oil-collecting bees, who gather the scent and appear to use it like cologne to attract a mate.

Learning which insects visit a particular plant and why can help us better understand species diversity among Anthurium. Using additional data, the team hopes to determine if these interactions have changed over time—building a more complete picture of these unique plants and the ecosystems that support them.

A Living Laboratory

This is not the first time the Garden’s extensive living collection of aroids has been used for scent research. With more than 1,200 aroids, including more than 500 Anthurium, the collection is frequently used by scientists who want to study the plants without having to track down a specimen in the wild. Some of these plants are so new to science, they have yet to be properly described and named as new species.

The aroid greenhouses at the Missouri Botanical Garden. Photo by Cassidy Moody.

While the aroid greenhouses are closed to the public, the Garden’s Climatron conservatory offers a chance for visitors to see the diversity of Anthurium first-hand. The Climatron is home to more than 100 Anthurium representing more than 40 species and hybrids. And if you visit at the right time, you might even catch a whiff of one as you walk by.