Stinking Flowers
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Volume 6 (Number 2) Summer 1997

This Issue Of Wayne's Word Is
Dedicated To Stinking Flowers
Not All Flowers Smell As Sweet As A Rose
Some Flowers Smell Like a Rotting Carcass & Attract
Blowflies and Flesh Flies To Their Showy Petals
© W.P. Armstrong 28 July 2010 (Revised 2 March 2013)
  1.    What Is A Carrion Flower?
  2.    Why Do Carrion Flowers Smell Rotten?
  3.    Perception Of Odors By Animals
  4.    Why Carrion Flowers Catch Insects?
  5.    Foul-Smelling African Starfish Flowers
  6.    The Rank And Remarkable Arums
  7.    The Flynapping Arum Of Sardinia
  8.    The World's Largest & Stinkiest Arum
  9.    A Putrid Root Parasite From Africa
10.    Stinking Corpse Lily: Largest Blossom
11.    Pilostyles: Relative Of Largest Flower?
12.    Putrid Flowers Of The Indian Almond
DISCLAIMER: The staff at WAYNE'S WORD assumes no responsibility for using any of the following flowers in a bouquet, corsage or floral arrangement. The size and weight of some of these blossoms could cause serious back injury if they are pinned to your lapel. In addition, they could negatively affect a loving relationship with a friend or spouse, especially when the floral stench attracts carrion insects and maggots. W.P. Armstrong, 1 June 1996.

A typical flower may be stereotyped as a colorful, sweet-smelling structure that attracts insects. A variety of insects find the showy petals and fragrance irresistible, and the reward for their pollination service is a carbohydrate-rich, sugary nectar secretion from the flower. While the above scenario fits the majority of flowering plants, there are many notable exceptions. Some plants rely on wind or water for pollination, and produce inconspicuous flowers with copious airborne or water-dispersed pollen. But of all the exceptions to the typical flower stereotype, some of the most remarkable are known as "carrion flowers," showy blossoms with the stench of rotting flesh.

Like the putrid, spore-laden fruiting bodies of phallus-like stinkhorn fungi that appear almost overnight in your garden, carrion flowers also entice flesh and fecal-loving insects to visit their stinking blossoms. They belong to a variety of different and unrelated plant families, and include some of the largest and most bizarre flowers on earth. The following fungi give off very unpleasant odors (at least to our noses) and attract some the same species of flies that visit carrion flowers.

Left: A flesh fly (Sarcophaga haemorrhoidalis) sitting on the head of a stinkhorn fungus (Phallus impudicus). Right: With the odor of fresh dog feces, the lantern stinkhorn (Lysurus mokusin) attracts green bottle flies (Phaenicia sericata) to disperse its spores.

Two common flies that are attracted to rotting flesh (carrion) and animal feces: A. Green bottle fly (Phaenicia sericata) of the family Calliphoridae. B. Flesh fly (Sarcophaga sp.) of the family Sarcophagidae.

  Other Stinkhorn Fungi That Attact Flies  

1. What Is A Carrion Flower?

Homology: Similarity Of Characteristics Due To Origin From A Common Ancestor.
Homoplasy: Similarity Due To Independent Origin From Distantly Related Ancestors

Pronunciation acc. to Merriam Webster: Homology (home-ALL-a-gee); Homoplasy (homo-PLAY-see)

Homology (Common Ancestor)
Homoplasy (Distant Ancestors)
1. Cactus spines & bud Scales in axillary bud. 1. North American cactus & African euphorbias.
2. Seed-bearing carpels & leaves. 2. Scorpion tail & antenna of S. American beetle.
3. Bones of bat wing & forelimb of human. 3. Wings of birds, bats & insects.
4. Bones of wing of bat & whale flipper. 4. Hummingbird & hawkmoth.
5. Pappus of composites & calyx. 5. Preying mantid & mantispid.

I prefer to use the terms homology and homoplasy when dicussing the evolution of similar characteristics. Homology refers to similarity due to a common ancestor. Characteristics derived from a common ancestor are termed homologous. Homologous organs are similar in structure and embryonic origin but are not necessarily similar in function. Cactus spines are homologous to bud scales of an axillary bud. Seed-bearing carpels of flowering plants are homologous to leaves because of their similarity in form, anatomy and development. The bone structure in the wings of a bat is homologous to the forelimbs of humans and other mammals. For example, a bat's wing and whale's flipper both originated from the forelimbs of early mammalian ancestors, but they have undergone different evolutionary modification to perform radically different tasks of flying and swimming. The penis and clitoris are also homologous organs. The presence of homology is evidence that organisms are related. Birds, bats and insects are not closely related and their wings are not homologous. Although they are all used for flight, they evolved independently in distantly related animals and are structurally quite different. Unrelated species with flowers that smell like carrion is not an example of homology because they are not closely related. They belong to very different and distantly related plant families. Stinking flowers in unrelated plant families is a good example of homoplasy or convergent evolution.

Homoplasy Includes Convergent & Parallel Evolution

Seed cones of female Ephedra californica.

An example of parallel evolution is the appearance of xylem vessels in the vascular tissues of very distantly-related plants, such as Ephedra in the gymnospermous division Gnetophyta and flowering plants in the angiospermous division Anthophyta (Magnoliophyta). In addition, species of Ephedra have double fertilization, where two sperm are involved in the fertilization process. Double fertilization was once thought to be a strictly angiosperm characteristic. Some older references have suggested that the Gnetophyta may represent a "missing link" in the evolution of flowering plants, but others say that vessels and double fertilization are examples of parallel evolution, and the Gnetophyta are more closely related to conifers than angiosperms. The current consensus among authorities (as of 2010) is that Amborella trichopoda (a primitive angiosperm without vessels) and all other flowering plants represent sister clades derived from an common ancester without vessels. This latter conclusion supports the independent (parallel) evolution of vessels in the Gnetophyta.

  Origin Of Flowering Plants: Angiosperms  

Three unrelated families of flowering plants all with bizarre flowers that emit the scent of carrion. Rafflesia arnoldii is a parasitic flowering plant native to Sumatra. It lives inside the stem of its host vine (Tetrastigma), only breaking through the stem surface as a large bud when it is time to flower. Hydnora africana is a root parasite on shrubby species of Euphorbia in South Africa. The Malaysian-Indonesian) Amorphophallus titanum grows from an enorous tuber up to 6 feet (2 m) in circumference and weighing up to 120 pounds (54 kg). The massive "flower" is technically an inflorescence composed of numerous small, unisexual male and female flowers. The minute flowers are clustered around the base of the erect spadix, within the showy, vase-shaped, pleated spathe. The 8 foot phallus-like spadix of A. titanum rivals the size of a blue whale penis. It is sometimes called the "stinking corpse lily," although this descriptive common name is more commonly applied to Rafflesia arnoldii.

The recently discovered cerambycid beetle Onychocerus albitarsis in Peru is truly one of the most remarkable examples of convergent evolution (homoplasy). It is described by A. Berkov, N. Rodriguez and P. Centeno in Naturwissenschaften Vol. 95, March 2008. Venom-injecting structures have arisen independently in unrelated arthropods, including spiders, centipedes and antlions. The venom is injected through hollow fangs (poison jaws), or in the case of centipedes, through modified forelegs. Among insects only wasps, bees and ants of the order Hymenoptera are known to possess true stingers. Microscopic examination of the newly discovered beetle has revealed that the tip of each antenna is truly a stinging device. In fact, Mr. Centeno discovered this fact first hand. As he grabbed the beetle, the insect jerked back its antennae and pricked his finger, which swelled as if stung by a bee. This is the first example of a stinger in the enormous beetle order Coleoptera.

A hypothetical cladogram showing the origin of a similar stinging device in two distantly related groups of arthropods that is not present in their nearest common ancestor. These stinging organs are not homologous. Although they are remarkably similar in appearance and function, they are structurally quite different. One is the modified terminal segment of a tail, and the other is from the terminal segment of a beetle antenna.

The terminal antennal segment of Onychocerus albitarsis has two pores opening into channels leading to the pointed tip through which the venom is delivered. The delivery system is almost identical to that found in the stinger of certain scorpions. Since beetles and scorpions belong to entirely different arthropod orders and are only distantly related, this is a dramatic example of homoplasy: similarity due to independent origin that is not from a common ancestor. In this case the homoplastic characteristics (stinging devices) evolved independently from each other. Although the article in Naturwissenschaften uses the term "convergent evolution," one might argue that this is "parallel evolution." The term homoplasy makes this confusing distinction unnecessary.

A small mantispid and a preying mantis. Although they differ greatly in size, these two insects are remarkably similar in appearance. They both have triangular heads with large eyes and a pair of raptorial (grasping) front legs. Their other two pairs of legs are used for walking. They belong to two very different insect orders. Mantids have incomplete metamorphosis (egg-nymph-adult) while mantispids have complete metamorhosis (egg-larva-pupa-adult). Although mantids were once placed in the order Orthoptera along with grasshoppers, crickets and cockroaches, they are now placed in the separate order Mantodea. Mantispids belong to the order Neuroptera, along with lacewings, snakeflies and antlions. Their remarkable adaptive similarity is an example of convergent evolution (homoplasy).

Flower "scent mimics" that lure carrion insects into their putrid blossoms are some of nature's most fascinating and successful experiments in evolution. They certainly represent some of the most fantastic examples of floral diversity. Although they include some of the largest and showiest blossoms in the world, they will probably never be used in a floral arrangement on your dining room table.

  Homoplasy: Parallel & Convergent Evolution  

Unlike the fragrant blossoms that attract bees, butterflies and moths, carrion flowers simulate the odor of a rotting carcass and attract carrion beetles and a variety of flies including blowflies, flesh flies and midges. Not only do these flowers smell like a dead animal, but their petals are typically flesh-colored, often with a dense covering of hair. The orchids Bulbophyllum and Pterostylis contain spot patterns or "warts" that imitate clusters of flies already enjoying a meal, and movable parts in the flower that catapult or maneuver the fly into a position of contact with the pollen masses (pollinia) or receptive stigma. Although not true carrion flowers, there are many other species with slightly malodorous flowers that attract flies, including a number of orchids and the male flowers of carob trees (Ceratonia siliqua).

Malodorous Male Flowers Of Carob Tree (Ceratonia siliqua)

The flowers and pods of the carob tree (Ceratonia siliqua) often arise directly from the limbs and branches of female trees. This species is predominately dioecious, with separate male and female trees; however, trees with both male and female flowers also occur in carob populations. Male flowers smell like human semen, the odor of which is caused (in part) by amines. The pods (mostly mesocarp or pulp) are ground to make carob flour which is used as a chocolate substitute in candy, ice cream, brownies and cookies. Since chocolate contains the alkaloid theobromine which is toxic to some mammals, carob is used in chocolate flavored treats for dogs. Locust bean gum, a thickening agent in ice creams and salad dressings, comes from the ground seeds of the carob tree. The name St. John's bread comes from the fact that carob trees were the "locust" on which John the Baptist fed. In ancient times, carob seeds were used as units of weight for small quantities of precious gemstones because they were extremely uniform is size. An average carob seed weighs about 3 1/3 grains, just over 200 milligrams. [Note: Some references give 4 grains for a carob seed.] The "carat," our present-day, international unit for the weight of diamonds, is derived from the name "carob," in reference to carob seeds. One carat is precisely 200 milligrams.

Cauliflory: Flowers and seed pods often grow directly from the main branches.

Seeds of the carob tree (Ceratonia siliqua) were once used as a standard for weighing precious gemstones. The brass weight in photo is exactly one gram (1000 milligrams), or about 5 carob seeds. The "carat" is our present-day, international unit for the weight of diamonds. Carat is derived from the word "carob," in reference to the carob seed. One carat is precisely 200 milligrams. The diamond in the engagement ring shown above is 1.09 carats or 218 milligrams. Karat spelled with a "k" refers to the fineness or purity of gold. One karat is 1/24 or 4.2 percent pure gold in an alloy. 16-karot gold is 16/24 or 66.7 percent pure gold, while 24-karat gold is 24/24 or 100 percent pure gold.

2. Why Do Some Carrion Flowers Smell Like Flatulence?

Carrion insects feed on feces, rotting flesh and other decaying organic matter, and they also lay their eggs in these damp, putrid-smelling places. Carrion flowers are masters in the art of deception because they lure these insects into their blossoms. The flowers get pollinated but the fate of the insects is much more dismal--maggots hatching from eggs laid by them will perish from lack of any suitable food. Unlike typical insect-pollinated flowers, most carrion flowers do not waste precious energy on rewarding its pollinators with copious nectar. The overpowering stench of some carrion flowers may be caused (in part) by putrescine (1,4-butanediamine) and cadaverine (1,5-pentanediamine), relatively simple amine compounds derived from the amino acids ornithine and lysine. Even in low concentrations of 5 to 10 parts per billion they are detected by the human nose. Putrescine is formed from the decarboxylation of the amino acids arginine and ornithine. Cadaverine is a decarboxylation product of the amino acid lysine. These potent, foul-smelling amines are also produced during the decomposition (putrefaction) of rotting proteins. One of the warning tests for deadly botulism poisoning in spoiled food is the presence of rotten-smelling amines produced by proteolytic strains of the anaerobic bacterium Clostridium botulinum. Amines are also produced by the action of intestinal bacteria and are often released in a flammable mixture of volatile gases (including carbon dioxide, hydrogen, hydrogen sulfide and methane) during the phenomenon known as flatulence. In fact, some of these noxious gasses and incompletely oxidized hydrocarbons do not meet the emission control standards established by the Environmental Protection Agency (EPA). It has been suggested that serious flatulence offenders should be required to pass stringent biennial smog control sniffer tests, just like internal combustion air pollution devices.

Blossoms of certain members of the arum family (Araceae) release volatile dimethyl oligosulphides to attract blowflies. These molecules have the unpleasant odor of rotten eggs and animal feces. Dimethyl sulfides include dimethyl disulphide and dimethyl trisulfide. They are present in arums such as Amorphophallus and Helicodiceros. They are also present in some of the bad-smelling stinkhorn fungi.

With the odor of fresh dog feces, the lantern stinkhorn (Lysurus mokusin) attracts green bottle flies (Phaenicia sericata) to disperse its spores. The decaying "lantern tip" also shows an Argentine ant (Iridomyrmex humilis = Linepithema humile).

Skatole: 3-methylindole (C9H9N)

Skatole is produced in the phallux-like spadix of some arums. It occurs naturally in feces from the breakdown of the amino acid trytophan in the mammalian digestive tract. Although it has a strong fecal odor, in low concentrations it has a fragrant flowery smell and is actually used in perfumes. Its name is derived from the Greek "skato" meaning dung. Scatology is the study of animal droppings.

  See Wayne's Rocky Mountain Scat Collection  
Illustrations by Ben Mills (2007, 2012), CCoil (2008) & Giorgiogp2 Courtesy of Wikimedia Commons

3. The Perception Of Odors By Different Animals

It is interesting to speculate about how different species of animals perceive odors, and why certain putrid odors are repugnant to us but are irresistible to carrion insects. Whether a particular odor is perceived as "bad" or "good" is in the nose of the beholder. In the case of humans, there is certainly an innate or learned adaptive advantage in associating foul-smelling food with illness and disease-causing microbes; however, blowflies perceive these same odors as a potential meal for themselves and their ravenous maggot offspring. The actual triggering mechanism that excites female flesh flies and blowflies (families Sarcophagidae and Calliphoridae) to lay their eggs in damp, putrid places, such as fresh feces and carrion, is probably a lot more complicated.

During warm weather, egg-laying blowflies can locate a dead carcass or stinking flower within hours. They can smell the odor of a fresh, rotting carcass up to a mile away. Generally, blowflies are not as strongly attracted to a carcass that has mummified due to prolonged desiccation in dry weather. Even with external mummification, the carcass may be attractive to blowflies if the abdominal cavity is torn open by carnivores or scavengers. The stages (larval instars) of maggot development can be used to approximate the age of a rotting animal carcass. Each larval instar has a time window before it molts (sheds its chitinous exoskeleton) and develops into a second (larger) stage. In typical blowflies there are three distinctive larval instars before the maggot stops feeding and undergoes metamorphosis into a pupa within a protective chitinous skin (puparium). During pupation, the pupa transforms into an adult male or female blowfly which exits the puparium and flies away to mate. Depending on the precise stages of blowflies that are found on a carcass or during an autopsy, the forensic entomologist can simply count back to determine the approximate date when the deceased body was available to egg-laying flies. This evidence was crucial testimony for the defense in the San Diego trial of David Westerfield; however, after hundreds of hours of testimony, the jury found Westerfield guilty.

Aristolochiaceae (Pipevine or Birthwort Family)

4. Why Do Some Carrion Flowers Incarcerate Insects?

In some carrion flowers the insects are lured into dark openings leading to the putrefying interior where they become trapped among the floral organs. This strategy insures cross pollination, especially when the male anthers release pollen several days after the female stigma is no longer receptive. When the imprisoned insects are allowed to leave they are given a thorough dusting of fresh pollen to be taken to a different plant. One of the classic insect-trapping carrion flowers is the European Dutchman's pipe (Aristolochia clematitis), a member of the birthwort family (Aristolochiaceae). The unusual common names are derived from the curious blossoms with a shape reminiscent of Sherlock Holmes' pipe, and an old herbal remedy. Some species in this family have aromatic roots that were reputedly used as a purgative to induce labor, a questionable practice that is not recommended. The curious blossoms of some species superficially resemble a human fetus in the womb, and the plants were once thought to facilitate child birth. During medieval times, various ailments were treated with plants that resembled certain afflicted parts of the body. This practice was called the "Doctrine of Signatures," and became the basis of medical treatment for centuries to come. The striking, tubular flower of Dutchman's pipe is held upright as it emits a foul, pungent odor. Small gnats land on the vertical upper calyx surface but slip down through the floral tube and into the inflated "pipe chamber" due to slippery wax granules on the inner surface. Dense, downward-pointing hairs in the floral tube prevent the gnats from climbing out. During their incarceration the gnats receive rations of nectar. Several days later, when the anthers release pollen, the jail hairs wilt and the flower tilts horizontally, allowing the pollen-laden gnats to walk out of their prison, and into another receptive floral trap on a different plant.

Dutchman's pipe (Aristolochia clematitis) Photo by H.Zell (2009) Wikimedia Commons

Aristolochia fimbriata, an interesting Dutchman's pipe native to Argentina. Small flies landing on the erect upper calyx lobe slip down into the inflated, pipe-like chamber below.

There are approximately 350 species of Aristolochia, mostly from tropical regions of the world. Many species have ingenious insect traps and malodorous, often nauseating stenches when the blossoms first open. One of the largest and most bizarre flowers on earth is the Brazilian Dutchman's pipe (A. gigantea). The showy maroon calyx-like corolla is the size of a large dinner plate (30 centimeters) across), with an "inviting" orifice leading into an inflated, bladder-like trap. Another unusual Dutchman's pipe native to northern California (A. californica) has much smaller blossoms that are pollinated by fungus gnats. Species of Aristolochia (often called pipevines) are the host for the pipevine swallowtail, a beautiful blue butterfly with bright red caterpillars.

This butterfly larva (Battus philenor) typically feeds on plants of the genus Aristolochia known as pipevines. In fact, toxins in the host plant are conferred to the larva and adult moth, giving them protection from predators. This striking caterpillar belongs to the swallowtail butterfly family (Papilionidae). When I took this photo I didn't realize that the host plant was Watson's Dutchman's pipe (Aristolochia watsonii) native to the Arizona desert region. Special thanks to Douglas Ripley for the identification.

Photo by Greg Hume (2012) Courtesy of Wikimedia Commons
Pipevine swallowtail (Battus philenor): Swallowtail family (Papilionidae).

Arizona Pipevine (Aristolochia watsonii) Flower & Fruit

The family Aristolochiaceae belongs to the order Piperales in the non-monocot, non-eudicot angiosperm group called the magnoliid clade or "magnoliids." According to W.S. Judd, et al. (2008), this clade is probably monophyletic and also includes the primitive orders Magnoliales, Laurales, and Canellales.

  Judd, W.S., Campbell, C.S., Kellogg, E.A., Stevens, P.F., and M.J. Donaghue. 2008. Plant Systematics: A Phylogenetic Approach (Third Edition). Sinauer Associates, Inc., Sunderland, Massachusetts. 611 p.

  See Bright Red Larva On Aristolochia watsonii In Arizona)  

A Dutchman's pipe (Aristolochia californica) native to the Coast Ranges of Central and Northern California, and foothills of the Sierra Nevada. This California species is pollinated by fungus gnats.

The bizarre flower of a Brazilian Dutchman's pipe Aristolochia gigantea. The front view (left) shows a central yellow spot where an opening leads into an enclosed pouch. The back view (right) superficially resembles a pair of lungs with a canal leading into an inflated, stomach-like pouch. The blossom is over 14 inches (36 cm) long.

Apocynaceae (Dogbane Family): Formerly In The Asclepiadaceae

5. The Foul-Smelling Starfish Flowers Of Africa

Some of the most notorious carrion flowers belong to the milkweed family (Asclepiadaceae), a very diverse plant family characterized by milky-white sap. Several South African succulent genera, including Stapelia, Caralluma and Huernia, resemble spineless, sprawling cacti with strange starfish-shaped flowers. The flesh-colored, hairy blossom of S. gigantea may be 8 to 10 inches across (20-25 cm), with a nauseating stench. Fringes of soft white hairs on the reddish-brown petals superficially resemble a layer of mold growing on rotting matter (at least through the compound eyes of carrion insects). Occasionally grown in southern California, the curious flowers attract flies and maggots when they are in full bloom. Another South African species, S. flavirostris, has strange blossoms that look and smell more like a furry, dead animal than a flower. The striped "zebra flowers" Huernia zebrina also produce an intensely fetid odor as they lie on the desert sands of South Africa. Another genus of climbing milkweeds (Ceropegia) produces striking, malodorous blossoms shaped like a wine glass, often with glistening cilia to attract flies. Like Aristolochia, they detain their visiting flies until the male flowers are mature.

Left: The putrid-smelling blossom of Stapelia asterias var. lucida looks and smells more like a hairy, star-shaped piece of rotting flesh than an actual flower. Right: Another bizarre Stapelia flower. The anthers are visible on the lower side of the blossom. Like other species of Stapelia, the blossom resembles a reddish, hairy piece of rotting flesh, both in appearance and smell.

Close-up view of a starfish flower (Stapelia gigantea) showing several green bottle flies (blowfly family Calliphoridae). The flies have laid small white eggs on the hairy flower surface; however, there is no hope of survival for the tiny maggots that will soon hatch. Although the flower gives off the exact odor of rotting flesh, it provides no food for the blowfly larvae. The benefit of this clever carrion masquerqade to the flower is pollination by blowflies, ideally from another starfish plant.

Close-up view of the edge of a starfish flower (Stapelia gigantea) showing hair and white, blowfly eggs.

Two additional carrion flowers native to South Africa: A. Huernia schneiderana. B. Stapelia flavirostris.

A. Ceropegia haygarthii, a member of the Apocynaceae related to Stapelia. B. Stapelia variegata.

Araceae (Arum Family)

6. The Rank And Remarkable Arums

The arum family (Araceae) is a large tropical family containing many popular cultivated genera, including Anthurium, Caladium, Philodendron, and Dieffenbachia. Recent studies using chloroplast DNA indicate that the arum family also contains the duckweeds, previously placed in the family Lemnaceae. Duckweeds include Wolffia, the world's smallest flowering plant, a passion of this author and the derivation of his Internet name of "mrwolffia." It also contains some of the most fascinating and bizarre carrion flowers on earth. Like the common garden calla, Zantedeschia aethiopica, the small unisexual flowers are packed along the base of an erect, phallus-like central spadix, typically with male flowers above the female. The spadix emerges from a vase-shaped or funnel-like modified leaf or spathe which is often brightly colored. Probably the best-known North American species is the skunk cabbage (Symplocarpus foetidus) of the eastern United States. A showy western skunk cabbage (Lysichiton americanum), with a bright yellow spathe, has a somewhat skunky odor, but not really the offensive stench of its eastern counterpart. The "skunk cabbage meadows" depicted on trail guides to the southern California mountains actually refers to corn lilies (Veratrum californicum), a member of the lily family (Liliaceae). The European relatives "lords-and-ladies" (Arum maculatum) and "dragon arum" (Dracunculus vulgaris) emit rather unpleasant odors resembling carrion or fresh feces. They are definitely not recommended in a bouquet or floral arrangement--unless you are trying to convey a message from a jilted lover. Although these plants are inconspicuous most of the year, their showy spathes and stench are unmistakable during late spring and summer.

  Family Araceae Subfamily Lemnoideae (Formerly Lemnaceae)  
DNA Cladogram Of Family Araceae Including The Duckweeds

Heat Production In Aroid Spadices

The spadix of some aroids produces a remarkable amount of heat during cold weather. In fact, the temperature of the spadix can be up to 30 degrees Celsius above a cool air temperature of 10 degrees Celsius. This may stimulate the activity of pollinator insect visitors and help to vaporize the stench of the flowers. The heat mechanism may involve male flowers packed around the spadix. In some species in which the upper part of the spadix is sterile (flowerless), the heat mechanism appears to be in the cells of this sterile tissue. Like heat-producing tissue in mammals, the cells in these flowers rapidly oxidize lipids and carbohydrates, thus releasing heat. Heat production in aroids is discussed in a fascinating article by R.S. Seymour in Scientific American, March 1997.

Yellow skunk cabbage (Lysichiton americanum), a showy arum native to the Pacific northwest. Unlike some of its fetid-smelling relatives, the flower emits a slightly skunky odor. This remarkable plant is also an important laxative for black bears emerging from hibernation.

Black bears are common in this western hemlock temperate rain forest near Ketchikan, particularly when the steams and rivers are teeming with salmon. The forest understory also contains other bear forage plants, including salmonberry (Rubus spectabilis) and yellow skunk cabbage (Lysichiton americanum). The latter plant belongs to the pantropical arum family (Araceae), including many cultivated ornamentals such as Anthurium, Caladium, Philodendron, Dieffenbachia, and the common garden calla (Zantedeschia aethiopica).

Regarding black bears in this area, skunk cabbage is especially noteworthy because it provides them with a natural laxative. During months of winter hibernation, bears become very constipated. In fact, black bears can go 100 days without eating, drinking, urinating, defecating, or exercising. When they emerge from their dens in the spring, they seek out and consume skunk cabbage. This diet restores their normal (regular) bowel movement cycle.

A. The purplish-red spathe and foul-smelling stench of the European dragon arum (Dracunculus vulgaris) attracts flies to the base of its erect, flower-bearing spadix. Although it is colorful, this is probably NOT the flower to give to that special someone in a bouquet. B. The South American Synandrospadix vermitoxicus, another beautiful arum with stinking flowers.

7. The Amazing Flynapping Arum Of Sardinia

Illustration by Louis van Houte (1849) Courtesy of Wikimedia Commons
Another remarkable arum called "dead-horse arum" (Helicodiceros muscivorus) with an ingenious fly trap is native to the rocky Mediterranean islands of Sardinia and Corsica. With a stench reportedly as strong as a sheep carcass, blowflies are lured into the fetid aperture at the base of the funnel-like spathe. Behaving as they would in a real carcass, the flies force their way into the neck past the spadix and down into the pitch-dark chamber itself. Carrying pollen from another plant, they inadvertently pollinate the receptive female flowers at the base of the chamber. Unable to escape from the chamber due to a dense rosette of stiff hairs, the flies remain prisoners until the male flowers above the stiff hairs start to release pollen. Then the barricade of hairs wilts and the flies are able to escape, getting dusted with pollen as they leave the damp and putrid-smelling chamber.

A brief article about olfactory mimicry in Helicodiceros muscivorus appeared in Nature 420: 625 (12 December 2002) by M.C. Stensmyr, I. Urru, I. Collu, M. Celander, B.S. Hansson and A-M. Angioy of the Swedish University of Agricultural Sciences. The authors determined the precise odor that attracted blowflies of the family Calliphoridae to the inflorecence of this species. Blowfly antennae were stimulated by three similar oligosulphides: dimethyl monosulfide (DMMS), dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS). All three volatile compounds were identified using gas chromatography (GC) with simultaneous flame ionization detection (FID). These oligosulphides are also produced by decaying meat during protein decomposition. The identical antennal responses to arum and carcass odors indicate that a carrion fly cannot rely on odors alone to separate the model (decaying meat) from the olfactory mimic (arum inflorecence). This is yet another example of sexual deception where the plant exploits insects for pollination purposes. It is interesting to note that DMMS is a primary irritant in humans. DMDS and DMTS are volatile compounds found in onions and garlic. In small concentrations, they are also important flavor components of grain spirits such as whiskey.

  Why Do Oligosulfides Burn Your Eyes?  

8. The World's Largest And Stinkiest Arum

The most remarkable carrion arum is the titan arum or bunga bangkai "corpse flower" (Amorphophallus titanum). Native to equatorial tropical rain forests of Sumatra, Indonesia, this amazing plant flowered at the New York Botanical Garden in 1937. At its maximum development, a spadix over 8 feet tall (2.4 m) emerged from a huge vase-shaped, pleated spathe over 4 feet (1.2 m) tall and 12 feet (4 m) in circumference. This floral giant developed from a tuber measuring 6 feet (2 m) in circumference and weighing over 100 pounds (46 kg). According to B. Meeuse and S. Morris (The Sex Life Of Flowers, 1984), the enormous blossom generates such an overwhelming smell that people have been known to pass out from taking too close a whiff.

Right: The magnificent titan arum (Amorphophallus titanum) at the Huntington Botanic Garden on August 3, 1999 (one day after its peak blooming period). The large, funnel-shaped spathe (red on the inner surface) is already folded closed in photo. Thousands of people witnessed this very unusual blossom. Those lucky enough to be at Huntington Botanic Garden on the previous day (August 2) saw this spectacular inflorescence with the reddish spathe opened wide, resembling the drawing on the commemorative T-shirt (right), for sale at HBG. To find out more about this amazing plant (or T-shirt) log on to the Huntington Botanic Garden web site at

  See Wayne's Word Amorphophallus T-Shirt  

Although the blossom of this arum may tower over an adult human, it is not the world's largest flower. It is technically an inflorescence composed of numerous small, unisexual male and female flowers clustered around the base of the spadix, within the showy, funnel-shaped spathe. Female flowers consist essentially of ovule-bearing pistils deep within the spathe. Staminate (male) flowers (consisting essentially of stamens) are packed around the spadix, just above the female flowers. The conspicuous upper part of the spadix is sterile (flowerless) and emits the stench. Since the male and female flowers reach maturity at different times, cross pollination between different plants is the normal mechanism for sexual reproduction and seed production. Female flowers are typically receptive before the anthers release pollen, a cross pollination incentive known as protogyny. After pollination, the minute female flowers give rise to several hundred seeds. Although truly magnificent, this inflorescence is rather small compared with the Bolivian bromeliad Puya raimondii, with a flower stalk 35 feet (11 m) tall bearing over 8,000 white blossoms. In case you are wondering about the generic name Amorphophallus, it is derived from the Greek words "amorphos" (shapeless) and "phallos" (penis). Actually, the 8 foot phallus-like spadix of A. titanum rivals the size of a blue whale penis. This remarkable arum flowered in spring of 1996 at the University of Bonn Botanical Garden in Bonn, Germany.

  See Edible Spadix Of Monstera Deliciosa  

On August 2, 1999 an Amorphophallus titanum achieved full bloom at the Huntington Botanic Garden in San Marino, California. This was only the 11th recorded bloom in the United States and the first ever in California. Equally astonishing was the number of people who came to visit this magnificent plant on the peak day of its blooming period, over 10,000 admirers. They waited patiently in a long line in 80-90 degree heat, a line that at one time extended the length of two football fields (or about 200 meters). Some people wore protective nose masks, and one boy even wore a gas mask. Actually, no one was overcome by the stench (the plant was roped off to prevent people from getting their faces too close to the funnel-shaped spathe).

On the 14th of June 2000, another remarkable Amorphophallus titanum was in full bloom at the Fullerton Arboretum on the campus of California State University at Fullerton (CSUF) in Orange County, California. Known affectionately as "Tiffy Titan," the plant came from one of two tubers donated to the CSUF Department of Biological Science in October 1994. [Incidentally, Tiffy's name is derived from Titan, the mascot for CSUF.] Both tubers came from seeds that were planted the previous year. The typical life cycle of A. titanum starts with a seed that develops into a dormant tuber, followed by leaf production, larger dormant tuber, flowering and seed production. At CSUF, the complete life cycle has taken seven years. Pollen from another A. titanum that bloomed the previous summer (1999) at Huntington Botanic Garden was applied to all of the female flowers of "Tiffy Titan" at the peak day of flowering (14 June 2000).

A. Amorphophallus titanum in full bloom at Fullerton Arboretum on the campus of California State University at Fullerton. B. Amorphophallus titanum near the end of its gigantic leaf stage. The withered compound leaf is supported by ties to the shadecloth ceiling framework. C. and D. Pollination of "Tiffy Titan" (Amorphophallus titanum) at Fullerton Arboretum on the campus of California State University at Fullerton. Pollinators are Leo C. Song Jr. of the CSUF Biological Science Greenhouse Complex and Chris Barnhill of the Fullerton Arboretum.

On July 16, 2002 another spectacular Amorphophallus titanum came into full bloom at Quail Botanical Gardens in Encinitas, California. The blossom (inflorescence) developed from a huge, tire-sized tuber in a large flower pot. As the spathe opened into a reddish-purple funnel surrounding the yellow spadix, the blossom emitted a powerful carrion stench that filled the air of this serene botanical garden.

  See A Giant Corpse Flower At Quail Botanical Gardens  

One of the original two tubers of Amorphophallus titanum donated to CSUF was still in its leaf stage on June 14, 2000 when "Tiffy Titan" was in full bloom. The single, enormous compound leaf was approximately eight feet tall (2.4 m) with a spread of at least 8 feet (2.4 m). It was already brown and withered, and was near the end of its leaf stage. Following the leaf stage, the enlarged tuber of this second A. titanum (with sufficient carbohydrate reserve) will hopefully produce another striking, stinking blossom.

Go To The Fullerton Arboretum Web Site at CSUF
Stages In Growth Of Amorphophallus paeoniifolius.
More Information At The International Aroid Society
Go To Home Page Of The International Aroid Society
Hand Pollination Of A. paeoniifolius By Scott Hyndman
  See Another Amorphophallus paeoniifolius In Malaysia  

Giant Tubers of Amorphophallus

Some references state that the tubers of Amorphophallus titanum are the largest in the plant kingdom. They may be 6 feet (2 m) in circumference and weigh up to 120 pounds (54 kg). However, tubers of tropical vines of the genus Dioscorea (Dioscoreaceae) may be over six feet long (2 m) and weigh 150 pounds (68 kg) or more. Edible Dioscorea yams commonly seen in tropical marketplaces are usually harvested at about 2-6 pounds (1-3 kg). In New Guinea and Melanesia, special ceremonial yams weighing over 120 pounds (54 kg) are grown to reflect the grower's status in the community. The yams are used for gifts and ritualized exchanges. A yam festival is held at harvesttime during which the tubers are covered by elaborate woven masks. There are reportedly yams in tropical Asia and the South Pacific that are much larger. An African species, called elephant's foot or Hottentot's bread (D. elephantipes) produces a huge woody tuber (caudex) weighing up to 700 pounds (318 kg). Technically it is called a caudex, an enlarged basal stem axis from which the stems and roots arise. The above-ground part of this caudex resembles the shell of a tortoise; hence the common name of "turtleback plant." Like other caudiciform xerophytes (desert plants with enlarged basal stems), the vine relies on carbohydrates and moisture stored in its caudex during extended periods of drought.

Dioscorea is a large genus of tropical vines with more than 600 species. The tubers of edible species are called yams, not to be confused with the sweet potato yam (Ipomoea batatas) of the morning-glory family (Convolvulaceae). Some Dioscorea yams are harvested for a natural steroid called diosgenin, the precursor for several synthetic steroidal hormones.

  True Yams: World's Largest Vegetable  

Another Bizarre Species Of Amorphophallus (A. paeoniifolius)

Another bizarre Malaysian species of Amorphophallus (A. paeoniifolius). Older references often list this species by its synonym of A. campanulatus. An enlarged, inflated, flower-bearing spadix protrudes from the vase-shaped spathe. Clusters of yellow male flowers (stamens) can be seen above the whitish stigmas of female flowers (pistils). Photo was taken at the Hawaii Tropical Botanical Garden, Papaikou, Hawaii. This remarkable arum was grown by Horticulturist and Garden Manager, Sean Callahan.

Gladiolus corm.
Many references refer to the underground storage stems of Amorphophallus as corms; however, they do not have a distinct basal plate. In typical corms, such as those of Gladiolus (left), the roots arise from the lower side of this basal plate. In Amorphophallus and other aroids, buds occur at the top of the tuber. The buds grow upward into a leaf or two and outward into roots with the tuber beneath (right). You can also take a noncommittal, intermediate position and refer to them as corm-like tubers or tuber-like corms!

Amorphophallus titanum tuber.
Image from Tindara Orchid
& Garden Supply Center

Tubers of Amorphophallus paeoniifolius compared with a tropical yam (Dioscorea alata).

  Wayne's Word Vegetative Terminology Part 1  
True Yams: The World's Largest Vegetable

Hydnoraceae (Hydnora Family)

9. A Stinking Root Parasite From Africa

Another interesting carrion flower Hydnora africana, a root parasite on shrubby species of Euphorbia in arid deserts of South Africa, attracts herds of carrion beetles. The salmon-red, flesh-colored flowers emerge from the sand and become literally crammed with black beetles. This curious flower belongs to the Hydnoraceae, a small family of unusual root parasites, some of which look more like the fruiting bodies of soil fungi than flowering plants. Another species (H. abyssinica) commonly parasitizes the roots of Acacia.

Photo by L. J. Musselman (2007) Courtesy of Wikimedia Commons
Hydnora africana, an unusual flesh-colored, parasitic flower that attacks the nearby roots of shrubby species of Euphobia in arid deserts of South Africa. The putrid-smelling blossom attracts herds of carrion beetles.

Rafflesiaceae (Rafflesia Family)

10. The Stinking Corpse Lily: World's Largest Flower

A related family of parasitic flowering plants (the Rafflesiaceae) contains the "stinking corpse lily" (Rafflesia arnoldii), the world's largest individual flower and truly a wonder of the plant kingdom. It has been called the "giant panda of the plant world" because this rare and endangered species only occurs in the rain forests of Sumatra and Borneo in the Malay Archipelago. Unlike most flowering plants, it has no leaves or stems and grows endoparasitically within the woody stems of its host vine Tetrastigma, a relative of the grape. Unless you saw evidence of an old blossom, you could walk right past a Tetrastigma vine without ever knowing that a complete Rafflesia plant lives inside its stem. Occasionally a large flower bud resembling a pale orange cabbage breaks through the bark of the host vine and expands into an enormous blossom up to 3 feet (0.9 m) in diameter and weighing up to 25 pounds (11 kg). The gigantic unisexual flower has five fleshy red lobes (sepals) spattered with raised white spots. With an odor reminiscent of a stinking corpse, the blossom attracts carrion beetles and flies which shuttle the pollen from male to female flowers. A single female flower may produce up to four million seeds which are dispersed by a variety of animals, from ants, tree shrews and squirrels, to the feet of wild pigs and Asian elephants. If a seed becomes lodged in a moist crevice on its host vine, it germinates and penetrates the host tissue where it proliferates into a network of microscopic filaments of cells. These fungus-like networks of vascular tissue eventually give rise to a mammoth blossom that pushes out through the host stem, making Rafflesia one of the most intriguing and unusual plants on earth. The chances of a seed finding a host vine are slim, and massive deforestation has further decreased the odds of this remarkable event. Recently the governments of Indonesia and Malaysia have begun to recognize the marketable curiosity value of this plant and ecological preserves are being established.

  See A Tetrastigma Vine Naturalized In The Hawaiian Islands  

Illustration by Graphic Artist E.M. Armstrong.

Copyright (C) ma_suska (2007) Courtesy of Wikimedia Commons.
The infamous "stinking corpse lily" (Rafflesia arnoldii), the world's largest flower. This remarkable Malaysian/Indonesian endoparasite lives completely within its host vine, and occasionally breaks through the bark as a huge bud that expands into an enormous blossom up to 3 feet (0.9 meter) in diameter.

Phylogeny of the Rafflesiaceae

Click on image to see slightly simplified polyphyletic version.

The precise evolutionary relationships between the Raflessiaceae and other families of dicotyledonous angiosperms have been elusive. A recent article in Science entitled "Floral Gigantism in Rafflesiaceae" by C.C. Davis, M. Latvis, D.L. Nichrent, K.J. Wurdack and D.A. Baum (11 Jan. 2007) has finally shed some light on this enigmatic plant family. The authors presented results of phylogenetic analyses of mitochondrial, nuclear and plastid data showing that Rafflesiaceae are derived from within the Euphorbiaceae (spurge family). Most euphorbs produce minute flowers, suggesting that the enormous flowers of Rafflesiaceae evolved from ancestors with tiny flowers. The authors estimate that for Rafflesia there was a 79-fold (7900 percent) increase in flower diameter in a period of about 46 million years. This is one of the most dramatic cases of size evolution ever reported for eukaryotes.

According to the Jepson Manual Of California Plants (2012), the traditional family Rafflesiaceae is polyphyletic, consisting of three main lineages belonging to different orders. Therefore, Pilostyles has been placed in the holoparasitic family Apodanthaceae along with Apodanthes and Berlinianche. Mitochondrial and nuclear DNA sequences confidently place the Apodanthaceae in the order Curcurbitales, where they also fit well in terms of their flower morphology.

  Pilostyles: Southern California's Most Unusual Wildflower  
The Large & Very Diverse Spurge Family (Euphorbiaceae)

Apodanthaceae (Stemsucker Family): Formerly In The Raffleciaeae

11. Pilostyles: California Relative Of Largest Flower

Note: Pilostyles Is Not A Carrion Flower, But Was Once Placed In Same Family As Raflessia
Ironically, a plant resembling a miniature Rafflesia grows in the Anza-Borrego Desert region of southern California. It is called Pilostyles thurberi, and like its Malaysian counterpart it grows completely within its host's stem. Only in the case of Pilostyles the host is a small, leguminous shrub called dyeweed (Psorothamnus emoryi). Like Rafflesia, male and female flowers appear from buds that break through the host stem, but quite unlike its gargantuan cousin, the fleshy red flowers are only about 3 to 5 millimeters in diameter. When they appear on the host stem, the buds of Pilostyles resemble small reddish pimples, but unlike a case of severe acne, the "pimples" open into minute blossoms.

Pollen-bearing (male) flowers.

Seed-bearing (female) flowers.

Pilostyles thurberi, a minute parasitic wildflower native to the Colorado Desert of the southwestern United States. Like its monstrous Asian counterpart, Rafflesia arnoldii, it lives completely within the stem of its host shrub. The head of an ordinary straight pin shows the small size of the blossoms. The host plant with fuzzy white stems and bright red glands is dyeweed (Psorothamnus emoryi) a member of the legume family (Fabaceae).

See Southern California's Most Unusual Wildflower
  See Pin Head Size Relationship Used On Wayne's Word  

Malvaceae (Mallow Family): Formerly In The Sterculiaceae

12. Putrid Flowers Of The Indian Almond

Stinking flowers are by no means limited to herbaceous perennials. In fact, a large rain forest tree of the Old World tropics called Indian almond (Sterculia foetida) produces masses of small, reddish-orange flowers with a disagreeable putrid stench. It belongs to the chocolate family (Sterculiaceae) and produces edible seeds inside large, woody pods called follicles. The oily seeds are eaten raw, roasted or fried; however, if consumed in excessive quantities the seeds may have a purgative effect. The smelly blossoms leave a long-lasting, putrid scent in your carrying case or pack. A Costa Rican tree in the custard-apple family (Annonaceae) called "palanco" (Sapranthus palanga) bears cauliflorous blossoms on the main trunk. The flowers are purplish-black when mature and have a strong musky odor resembling a rotting carcass. They are presumedly pollinated by flies or beetles which are attracted to the scent.

Flowers and a follicle seed pod of "stinky sterculia" or Indian almond (Sterculia foetida). A. View of seeds inside one follicle (carpel). B. Flowers from the inflorescence. C. Close-up view of one flower. D. Mature fruit composed of 5 many-seeded follicles. The speciific epithet foetida is derived from the putrid odor of the blossoms. This species is also called "Java almond" and the seeds are eaten raw, roasted or fried. It was formerly placed in the family Sterculiaceae; however DNA cladistical analysis shows that it belongs in the mallow family (Malvaceae). I once placed the flowers and seed pods of this tree into a luggage bag. The putred odor in my bag persisted for several years!

  Major Changes In Taxonomy Of The Malvaceae  

Flower "scent mimics" that lure carrion insects into their putrid blossoms are some of nature's most fascinating (and successful) experiments in evolution. They certainly represent some of the most fantastic examples of floral diversity. Although they include some of the largest and showiest blossoms in the world, they will probably never be used in a floral arrangement on your dining room table.

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