Pinanga Subterranea, Rare Palm Species Found in Kalimantan, Flowering Underground

Pinanga Subterranea, A rare palm species has just been discovered in Kalimantan. This species is the only member of the palm family (Arecaceae) known to flower and fruit almost entirely underground.

Because this rare palm species has such unusual characteristics, scientists named the species Pinanga subterranea. The word subterranea comes from Latin which means underground.

Researchers at the Royal Botanic Gardens, Kew and colleagues have outlined the discovery of this rare palm species in a new study paper. The paper has appeared in the journal PALMS with additional commentary in Plants, People, Planet.

Exposed subterranean Pinanga roots and fruit. Photo: Royal Botanical Gardens, Kew

Native to the tropical island of Borneo in Southeast Asia, this plant is famous among locals who enjoy snacking on its bright red fruit. The fruit of this rare palm species is a sweet and juicy food consumed in some parts of the island.

However, until now, the plant has remained unnoticed by scientists who to date have described around 300 different palm species on the island. Pinanga subterranea joins the more than 2,500 species of palms known to science, of which about half may be threatened with extinction.

According to an international research team, Pinanga subterranea can be found scattered throughout the primary rainforests of western Kalimantan, across state lines from Sarawak in Malaysia to Kalimantan in Indonesia.

Before being scientifically described, this plant was known in at least several Kalimantan languages as Pinang Tanah, Pinang Pipit, Muring Pelandok, and Tudong Pelandok.

Pinanga subterranea fruit is eaten and spread by bearded pigs but the method of fertilization is unclear. Photo: Royal Botanical Gardens, Kew

Hidden in plain sight

Although this rare palm species and its fruit are well known to the native people of Borneo, Pinanga subterranea has been completely ignored by the scientific community, much to the surprise of the researchers of this study.

According to the researchers, this highlights the need to collaborate more closely with indigenous communities and their complex knowledge of landscapes and forests.

In fact, researchers were first alerted to the plant’s existence by study co-author Paul Chai, a Malaysian botanist and namesake of the Pinanga chaiana palm species.

Paul first discovered this palm in 1997 during a visit to the Lanjak Entimau Wildlife Reserve, Sarawak. As he brushed away the thick leaf litter surrounding the young palm tree to get a better picture, he noticed the fruit that had been exposed.

There were several plants, but only one bore fruit. In 2018, Kew scientists Benedikt Kuhnhäuser, Peter Petoe, and William Baker revisited the Lanjak Entimau Wildlife Reserve and collected several specimens of the palm for scientific research.

“Without a tip from our Malaysian colleague Dr. Paul Chai, we might have mistaken this interesting new species for an unremarkable palm seedling and would have walked right past it,” said Benedikt Kuhnhäuser.

“Instead, we have scientifically described an extremely rare case of geoflory, namely underground flowering, and the first known example of its kind in the entire palm family. This is truly a once-in-a-lifetime discovery.”

Separately from the team, Indonesian researcher and lead author of the study, Randi Agusti, discovered several palm specimens in Kalimantan in 2017. At least one appeared to have been dug up by a wild boar, while others appeared to have been eaten or destroyed by the animal.

Researchers from Indonesia, Malaysia and Kew then worked together to scientifically describe this unusual palm as a species new to science.

Randi Agusti, a researcher from the National University of Singapore, said, “The first time I discovered this dwarf palm was in 2017 in a forest in West Kalimantan. A group of wild boars were digging in the ground around a population of P. subterranea, and I found several ripe fruits with a striking bright red color lying on the ground.”

“I noticed that a lot of the soil around this palm trunk was being dug up by wild boars to look for fruit underground. The feces were also scattered around the puddles of water with the seeds contained in them,” said Randi.

At first glance, this species looks like young plants of other common palms in the rainforests of Borneo. Palm seeds are often scattered on the forest floor in tropical rainforests and are very difficult to identify, even by the most skilled botanist, and as a result tend to be overlooked in botanical surveys.

But in this case, the visible seedlings are actually fully formed mature trees, with their reproductive parts hidden beneath the surface of the soil.

However, even with Dr. Chai, scientists still have to demonstrate the novelty of the species. There is more than 1

40 species of palms in the genus Pinanga.

The palm was already known to local people but it had remained unnoticed by scientists. Foto: William J Baker/Royal Botanical Gardens, Kew

Most of the species in this genus are small, erect palms that can be found along the forest understory. More than 100 of these species exist in Southeast Asia, and Kalimantan is the center of their diversity.

Distinguishing Pinanga subterranea as a truly new species required careful study by Randi, a Pinanga expert. Randi carefully compared this palm specimen to all other known Borneo species of this genus to build the argument that it is a new species to science.

The uniqueness of the Pinanga subterranean

Most flowering plants (angiosperms) have evolved to develop their flowers and fruit above the ground, which helps facilitate pollination and seed dispersal. But there are a small percentage of plants that have evolved to flower and fruit underground—processes known as geoflory and geocarpy respectively.

This geoflory and geocarpy phenomenon has been observed in at least 171 species in 89 genera and 33 plant families. Beans, for example, flower above ground, but their fruit develops underground.

However, fruiting and flowering exclusively underground is a very rare phenomenon. To the researchers’ knowledge, it has only ever been observed in the small orchid genus Rhizanthella.

This unusual behavior has puzzled scientists because it appears to hinder the plant’s ability to successfully pollinate and disperse seeds, and has never been observed before in the palm family. With the description of P. subterranea as new to science, the researchers hope it may interest other researchers who may help unravel some of the mysteries surrounding this unusual species.

William Baker, Senior Research Leader—Tree of Life at RBG Kew, says, “I have studied palms for 30 years and am amazed at how they continue to surprise us.”

“This unexpected discovery raises more questions than answers. What pollinated the palm tree? How did the pollinator find the flower underground? How did this phenomenon evolve and what will surprise us next with palm trees?”

In the case of the Pinanga subterranea, the dual example of geocarpy and geoflory is further confused because plants in the genus Pinanga are usually pollinated by insects such as bees and beetles, which cannot move as easily underground as they do above.

However, despite this oddity, scientists have observed a large number of seeds and fruit planted by Pinanga subterranea, which indicates a successful pollination mechanism. The study research team has not yet solved this mystery so it will require further study of the processes that occur in the soil.

However, the researchers were more successful in finding out how the plant’s seeds were dispersed in the rainforest. Observations have revealed that the fruits of the rare palm species are dug up and consumed by bearded pigs (Sus barbatus).

While the fruit doesn’t seem to have a distinct scent to the human nose, pigs’ much more subtle sense of smell can aid them in their hunt for food. Just like the pigs used to hunt for truffles.

The seeds from the fruit that the pigs eat are then scattered throughout the forest in the pig’s dung. Researchers have successfully cultivated seeds collected from the pig droppings, which have grown well in the Sylva Untan Arboretum in Indonesia as an ex-situ living plant collection.

Benedikt Kuhnhäuser added, “Identifying Pinanga subterranea as something new to science would not have been possible without the extensive reference of palm collections at botanical institutes in Indonesia, Malaysia and at Kew, as well as the decades-long expertise of our team in collecting and identifying palms.”

“This research is a reminder that we need to continue to invest in the next generation of collections of taxonomists and botanists to enable similar astounding discoveries in the future. There is still much to be discovered about our increasingly threatened natural world.”

Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Clade: Commelinids
Order: Arecales
Family: Arecaceae
Genus: Pinanga
P. subterranea
Binomial name
Pinanga subterranea

Randi & W.J.Baker[1]

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