Opossum Pollination of a Peculiar Parasite

Floral traits can provide us with insights into the types of pollinators most suited for the job. For many flowering plants, the relationship is relatively easy to understand, but check out the flowers of Scybalium fungiforme. You would be completely excused for not even realizing that these bizarre structures belonged to a plant. The anatomy of those flowers would leave most of asking “what on Earth do they attract?” The answer to this are opossums!

Scybalium fungiforme hails from a peculiar family of parasitic plants called Balanophoraceae and is native to the Atlantic forests of Brazil. Members of this family can be found in tropical regions around the globe and all of them are obligate root holoparasites. Essentially this means that all one ever sees of these plants are their strange flowers. The rest of the plant lives within the vascular system of a host plant’s roots.

The adorable big-eared opossums (Didelphis aurita).

Scybalium fungiforme is particularly strange in that its flowers are covered in scale-like bracts. As such, accessing the flowers would be difficult for most animals. Because its strange blooms superficially resemble some marsupial and rodent pollinated Proteaceae in Australian and South Africa, predictions of a non-flying mammal pollination syndrome were about the only explanations that made sense. Now, with the help of night vision cameras, this prediction has been vindicated.

They key to this unique pollination syndrome lies in those bracts and an interesting aspect of opossum anatomy. Until the scale-like bracts are removed, not much is able to access the floral parts inside. Luckily big-eared opossums (Didelphis aurita) come equipped with opposable toes on their back feet. Upon locating the flowers of S. fungiforme, the opossum uses its back feet to remove the bracts. This unveils a bounty of nectar within. As the opossum feeds, its furry little snout gets covered in pollen. When the opossum visits subsequent flowers throughout the night, pollination is achieved.

Floral visitors of Scybalium fungiforme. b) The big-eared opossum, Didelphis aurita drinking nectar on a plant with five inflorescences (one male and four females). c) The montane grass mouse, Akodon montensis, visiting a plant with about 10 inflorescences and drinking nectar on a female one. d) The Violet-capped Woodnymph hummingbird, Thalurania glaucopis visiting a male and e) a female inflorescence. f) detail of an A. angulata wasp manipulating a male flower to eat pollen. g) Agelaia angulate visiting a female inflorescence with the head inserted among flowers to reach the nectar secreted in the inflorescence receptaculum.

Interestingly, activity doesn’t end when the opossums are done. Enough nectar often remains by the next day that a suite of other animals come to pay a visit to these strange blooms. Day time visitation of S. fungiforme consisted largely of wasps, bees, and even a mouse or two. Researchers were also lucky enough to witness Violet-capped Woodnymph hummingbirds (Thalurania glaucopis) repeatedly visit the flowers for a sip of nectar. It would appear that although the main pollinators of this strange parasite are opossums, the removal of the bracts opens up the flowers for plenty of secondary pollinators as well.

Though this is by no means the only plant to be pollinated by non-flying mammals, this pollination syndrome certainly broadens our understanding of the evolution of pollination syndromes.

Photo Credits: [1] [2] [3]

Further Reading: [1]

The Smallest of the Giants

Photo by Edwino S. Fernando [source]

There are a lot of cool ways to discover a new species but what about tripping over one? That is exactly how Rafflesia consueloae was found. Researchers from the University of the Philippines Los Baños were walking through the forest back in 2014 when one of them tripped over something. To their surprise, it was the bloom of a strange parasitic plant.

This was an exciting discovery because it meant that that strange family of holoparasitic plants called Rafflesiaceae just got a little bit bigger. Rafflesiaceae is famous the world over for the size of its flowers. Whereas the main body of plants in this family consists of tiny thread-like structures living within the tissues of forest vines, the flowers of many are huge. In fact, with a flower 3 feet (1 meter) in diameter, which can weigh as much as 24 lbs. (11 kg), Rafflesia arnoldii  produces the largest flower on the planet. This new species of Rafflesia, however, is a bit of a shrimp compared to its cousins.

In fact, R. consueloae produces the smallest flowers of the genus. Of the individuals that have been found, the largest flower clocked in at 3.83 inches (9.37 cm) in diameter. Needless to say, this was an exciting discovery and those responsible for it quickly set about observing the plant in detail. Cameras were set up to monitor flower development as well as to keep track of any animals that might pay it a visit. It turns out that, like its cousins, R. consueloae appears to be a specialist parasite on a group of vines in the genus Tetrastigma.

One of the unique characteristics of R. consueloae, other than its size, is the fact that its flowers don’t seem to produce any noticeable scent. This is a bit odd considering that its cousins are frequently referred to as “corpse flowers” thanks to the fact that they both look and smell like rotting meat. That is not to say that this species produces no scent at all. In fact, researchers noted that the fruits of R. consueloae smell a bit like coconut.

Its discoverers were quick to note that the discovery of such a strange parasitic plant in this particular stretch of forest is exciting because of the state of disrepair the forest is in. This region has suffered heavily from deforestation and fragmentation and it has long been thought that such specialized parasites like those in the genus Rafflesia could not persist after logging. As such, this discovery offers at least some hope that they may not be as sensitive as we once thought. Still, that does not mean that R. consueloae is by any means secure in its future.

To date, R. consueloae has only been found growing in two localities in Pantabangan, Phillippines. Though it is possible that more populations will be found growing elsewhere, its limited distribution nonetheless places it at high risk for extinction. Further habitat loss and the potential for anthropogenic forest fires are considerable threats to these plants and the hosts they simply can’t live without.

Despite plenty of observation, no one is quite sure how this species manages to reproduce successfully. Individual flowers are said to be either male or female but without a scent, its hard to say who or what pollinates them. Similarly, it still remains a mystery as to how R. consueloae (or any of its relatives for that matter) accomplish seed dispersal. Some small mammals were seen feeding on fruits but what happens after that is anyone’s guess. It seems like the various Rafflesiaceae still have many mysteries to be solved.

Photo Credit: [1]

Further Reading: [1]

Rhizanthes lowii

Photo Credit: Ch'ien C. Lee - www.wildborneo.com.my/photo.php?f=cld1500900.jpg

Imagine hiking through the forests of Borneo and coming across this strange object. It's hairy, it's fleshy, and it smells awful. With no vegetative bits lying around, you may jump to the conclusion that this was some sort of fungus. You would be wrong. What you are looking at is the flower of a strange parasitic plant known as Rhizanthes lowii.

Rhizanthes lowii is a holoparasite. It produces no photosynthetic tissues whatsoever. In fact, aside from its bizarre flowers, its doesn't produce anything that would readily characterize it as a plant. In lieu of stems, leaves, and roots, this species lives as a network of mycelium-like cells inside the roots of their vine hosts. Only when it comes time to flower will you ever encounter this species (or any of its relatives for that matter).

The flowers are interesting structures. Their sole function, of course, is to attract their pollinators, which in this case are carrion flies. As one would imagine, the flowers add to their already meaty appearance a smell that has been likened to that of a rotting corpse. Even more peculiar, however, is the fact that these flowers produce their own heat. Using a unique metabolic pathway, the flower temperature can rise as much as 7 degrees above ambient. Even more strange is the fact that the flowers seem to be able to regulate this temperature. Instead of a dramatic spike followed by a gradual decrease in temperature, the flowers of R. lowii are able to maintain this temperature gradient throughout the flowering period.

Photo Credit: Ch'ien C. Lee - www.wildborneo.com.my/photo.php?f=cld1500900.jpg

There could be many reasons for doing this. Heat could enhance the rate of floral development. This is a likely possibility as temperature increases have been recorded during bud development. It could also be used as a way of enticing pollinators, which can use the flower to warm up. This seems unlikely given its tropical habitat. Another possibility is that it helps disperse its odor by volatilizing the smelly compounds. In a similar vein, it may improve the carrion mimicry. Certainly this may play a role, however, flies don't seem to have an issue finding carrion that has cooled to ambient temperature. Finally, it has also been suggested that the heat may improve fertilization rates. This also seems quite likely as thermoregulation has been shown to continue after the flowers have withered away.

Regardless of its true purpose, the combination of lifestyle, appearance, and heat producing properties of this species makes for a bizarrely spectacular floral encounter. To see this plant in the wild would be a truly special event.

Photo Credit: Ch'ien C. Lee - www.wildborneo.com.my/photo.php?f=cld1500900.jpg

Further Reading: [1] [2]