With Malodorous Intent

Posted on Tue., July 18, 2023 by Sandy Masuo
An Amorphophallus titanum in front of a glass window.

A Titan Arum (Amorphophallus titanum) in bloom is guaranteed to draw crowds of the curious, eager to experience one of the world’s most intriguing plants. But The Huntington’s botanical collections include a plethora of other plants that offer olfactory adventures throughout the year. | Photo by Jessica Pettengill.

A stroll through The Huntington’s gardens is a feast for the senses. Enhancing the beauty of the plants are the sounds of birdsong and breezes rustling through foliage, carrying with them the perfume of roses, gardenias, orange blossoms, and more. As scintillating as these scents are, however, plants do not produce them for our pleasure. Indeed, many flowers exude odors that are far from pleasant. Whether sweet or stinky, they share a common goal: reproduction.

Close-up of the spathe of an Amorphophallus titanum.

The upper portion of the Titan Arum flower stalk heats up to disperse the odor compounds that attract its pollinators. The tiny male and female flowers are located on the lower portion, concealed by the colorful spathe. | Photo by Brandon Tam.

Vibrant and fragrant flowers are advertisements that evolved to attract pollinators with the promise of food incentives: nectar and pollen. It’s an arrangement that demands considerable energy from plants for a service that pollinators passively provide. In addition to the nectar reward, the plant must produce enough pollen to feed the pollinators and ensure that some is carried away to the next flower. However, some plants conserve resources through deception. Scent is less expensive to produce than calorie-rich nectar, so these tricksters offer no food. Instead, the plants exploit insects not typically associated with pollination: flies, gnats, beetles, and others that feed on or deposit their eggs in decaying organic matter. When the insects explore what smells and looks like a hunk of rotting meat, a pile of excrement, or funky fungus—expecting a meal or place to mate—pollen clings to their bodies and they transport it to other plants.

A cluster of green leaves with two large burgundy blooms.

In Greece, part of its native range, Dracunculus vulgaris is known by the common name Drakondia, which is derived from “drakōn,” meaning “serpent” and the root of the word “dragon.” The black spadix resembles a black snake or a dragon tail. | Photo by Gary Roberson.

The Dragon Arum (Dracunculus vulgaris), a smaller relative of our infamous Titan Arum, is native to parts of the Mediterranean region. What it lacks in size, it makes up for in beauty, with deep green, frilly foliage and a maroon inflorescence that is (like all aroids) similar in structure to its behemoth cousin: a prominent stalk, or spadix, wrapped by a specialized leaf called a spathe. This arum, however, employs a more dramatic pollination strategy. Like the Titan, it lures flies and beetles with a putrid aroma. The Dragon’s female and male flowers are also located at the bottom of the spadix, but they are enclosed in a chamber that bulges at the base of the inflorescence. The pollinators slip inside it and are imprisoned overnight, their scrambling efforts to escape helping to ensure fertilization. The next morning, the spathe withers and the male flowers release their pollen, allowing the insects to escape while dusting them for their next Dragon Arum encounter. Since it originates in a climate similar to ours, this plant can be grown outdoors in much of Southern California. Like many of our native plants, it responds to winter rains with a spring floral display, then goes into summer dormancy as the dry season progresses. These Dragons make their home along The Huntington’s cycad walk and in the Subtropical Garden.

A cluster of burgundy flowers with white accents on a thick branch.

Plants in the genus Aristolochia attract flies for pollination by mimicking a range of odors. These A. arborea flowers also use an optical illusion to fool fungus gnats. | Photo by Sandy Masuo.

Plants in the Aristolochia genus are equally devious but gentler on the nose. The genus is made up of hundreds of species worldwide with flowers that range in smell from almost imperceptible (to humans) to a distinctly musty odor that appeals to gnats and other fungus feeders. Like the Dragon Arum, most feature floral chambers where confused pollinators are temporarily trapped to promote fertilization. The Subtropical Garden includes the Andalusian Dutchman’s Pipe (A. baetica), native to North Africa and the Iberian Peninsula. The Chilean Giant Dutchman’s Pipe (A. gigantea) grows in the Jungle Garden and one of the planters in The Rose Hills Foundation Garden Court. The Rose Hills Foundation Conservatory for Botanical Science (temporarily closed to visitors) houses three Aristolochia species, including A. arborea, an unusual tree form that is native to Mexico and Central America. It blooms for much of the year, and like many aristolochias, it is pollinated by fungus gnats. Inside the hoodlike maroon flowers nestle what appear to be mini mushrooms, which are, in fact, the traps that imprison the gnats.

Ferraria crispa (left) and Ferraria divaricata (right)

Ferraria flowers are richly textured and ornately colored. Various species attract different pollinators. | Photos by Gary Roberson.

Ferrarias are iris relatives native to southern Africa. Their elaborate flowers earn them the common name Starfish Lily. The blooms are richly textured and mottled with shades of cream, burgundy, yellow, purple, and brown. The fragrances of the 18 species that make up the genus vary from pleasant vanilla-like scents that appeal to wasps to a fetid odor that attracts flies. The Cycad Terrace south of the Huntington Art Gallery is home to three species that bloom in spring. F. crispa is best known as a garden stinker, and this species can also be found in the Subtropical Garden.

A large star-shaped flower grows among green succulents.

A variety of Stapeliads grow in the Desert Garden. Their carrion-like scent attracts flies in search of a meal or a place to deposit eggs. | Photo by John Sullivan.

Also from southern Africa are succulents in the genus Stapelia, commonly known as Starfish or Carrion Flowers. The blooms range in color from pale cream speckled with burgundy to deep ruddy shades. Many are hairy and most have a dark center where the reproductive organs are located. The odor they emit is irresistible to flies and beetles. The overall effect (from the insect perspective) is of a ripe carcass that has been opened by another scavenger—the perfect place to mate and deposit eggs because such a site would ensure that their hatched offspring have an ample food supply. It’s common to see tiny white fly eggs or squirming larvae lodged in the middle of the flowers. What you won’t see are conspicuous stamens covered in powdery pollen. Rather than producing loose pollen in copious enough quantities to both feed and dust the bodies of pollinators, these flowers pack pollen into sticky structures called pollinia.

A red star-shaped flower blooms among rocks and dirt.

Stapelia flowers are so convincing at mimicking carrion that it is not uncommon to find fly eggs and larvae scattered on them. | Photo by Linnea Stephan.

Stapelia pollinia, which form near slots in the center of the flowers, gently snare the insects’ legs and feet. As the insects pull free, the pollinia adhere to their bodies and are carried away to the next flower that looks and smells like a carcass. These succulents can bloom as early as late spring, but they usually put on their best floral display in the Desert Garden from late summer into fall.

A large cluster of red orchid flowers with a fuzzy texture.

As with other plants that lure flies for pollination, Bulbophyllum phalaenopsis produces flowers that mimic decaying flesh, in this case complete with small white filaments that suggest hairs or maggots. | Photo by Linnea Stephan.

Even a few orchids rely on deception. Bulbophyllum phalaenopsis flowers are a fleshy claret color with dark, inviting folds and white papillae that resemble maggots. These features fool carrion flies into thinking that they have found a suitable place to lay eggs, and, in the process, they pick up the flower’s pollinia. Native to tropical Papua New Guinea, this plant is housed in the Conservatory. The plant usually blooms in spring or early summer, depending on the temperature and humidity, and sometimes flowers twice in one season, occasionally at the same time as the Titan Arum.

By enticing beetles and flies to help them reproduce, these plants (and others in many different families) save energy and avoid having to compete for more conventional pollinators. The next time you stroll through the gardens and notice a plant’s foul odor, think of it as the “sweet” smell of evolutionary success.

Sandy Masuo is the senior writer in the Office of Communications and Marketing at The Huntington.