Rare Underground Flowering Palm Species Discovered in Borneo

Palm trees with their feathery fronds are a long-standing symbol of the tropics… aboveground. Now, researchers with Royal Botanic Gardens (RBC), Kew have documented a unique member of the Arecaceae, or palm, family that produces its flowers and fruits almost exclusively beneath the soil, a press release from RBC, Kew said.

The species, which the international research team dubbed Pinanga subterranea, is native to Borneo, a tropical island in Southeast Asia. The underground flowering plant was already known to locals who enjoy its juicy red fruit. Scientists had previously described about 300 palm species in Borneo, but had missed this particular palm.

“Without the tip-off from our Malaysian colleague Dr. Paul Chai, we probably would have mistaken this exciting new species for an unremarkable palm seedling and would have walked right past it. Instead, we have scientifically described an incredibly rare case of geoflory, that is underground flowering, and the very first known example of its kind in the entire palm family. It truly is a once-in-a-lifetime discovery,” said Dr. Benedikt Kuhnhäuser, Future Leader Fellow at RBG Kew, in the press release.

There are more than 2,500 documented palm species in the world, but as many as half of them could be in danger of extinction.

The new study of the unique palm species, “Hiding in plain sight: The underground palm Pinanga subterranea,” was published in the journal Plants People Planet.

The researchers said western Borneo’s primary rainforests are peppered with the subterranean palms. The plant had already been named in at least three languages on its native island and was known as Pinang Pipit, Pinang Tanah, Muring Pelandok and Tudong Pelandok.

“I realised the stems, flowers and fruit were underground after the soil was dug up by boars, so it was as if the boars guided me to find this palm,” said Agusti Randi, a researcher at the National University of Singapore, as reported by The Guardian. “It has a sweet taste, with quite thick flesh and a soft and juicy texture. We still don’t know about other uses of the plant, and there are many things that are still a mystery – for example, the process of pollination and who the pollinator is, and what causes this plant to produce flowers and fruit underground.”

The researchers said that the fact that Indigenous communities in Borneo were so familiar with the plant while it had been completely missed by scientists points to the necessity of working in tandem with Indigenous people to learn from their expertise concerning the local landscape and its flora, the press release said.

“The first time I encountered this dwarf palm in 2017 in a forest in West Kalimantan, a group of wild boars were digging in the soil around a population of P. subterranea, and I found several ripe fruit with a striking, bright red color lying on the ground. I noticed that a lot of the soil around the stems of this palm was dug up by the wild boars to find the fruit that was underground. Their feces were also strewn around in puddles with the seeds contained in them,” Randi said in the press release.

Co-author of the study Dr. Paul Chai, a botanist from Malaysia who the species of palm Pinanga china was named after, told the researchers about the underground palm. Chai first unearthed P. subterranea in 1997 while visiting Lanjak Entimau Wildlife Sanctuary in Sarawak, Malaysia.

Randi’s initial encounter with the palm was in 2017 in Kalimantan.

After these encounters, Kew researchers, along with those from Malaysia and Indonesia, got together to give the plant an official scientific description.

“Pinanga subterranea is the only known species of palm to flower and fruit below ground,” Kuhnhäuser said, as The Guardian reported. “Flowering and fruiting below ground is mind-boggling and seemingly paradoxical because they appear to prevent pollination and dispersal. We now know bearded pigs eat and disperse Pinanga subterranea’s fruits, but we’ve yet to find out how and by whom the flowers are pollinated.”

Palm plant seedlings tend to cover the tropical rainforest floor, and Pinanga subterranea resembles common juvenile Bornean palms, so it was overlooked in botanical surveys.

The scientists had to distinguish the underground palm species from the more than 140 other palm species in the genus Pinanga. More than 100 of them are found in Southeast Asia, with Borneo having the most diverse range of species.

Most flowering plants flower and fruit above ground to make pollination and seed dispersal easier. There are at least 171 plant species that produce flowers or fruit below ground, with a well-known example being the peanut, which produces its fruit underground after flowering above the surface. Flowering and producing fruit entirely in the soil is very rare, however, with the only other example being the orchid genus Rhizanthella, as far as the authors of the study were aware.

“I have been studying palms for 30 years and am amazed at how they continue to surprise us. This unexpected find poses many more questions than it answers. What is pollinating the palm? How does the pollinator find the flowers underground? How did this phenomenon evolve and what on Earth will palms surprise us with next?” said Dr. William Baker, Senior Research Leader at Kew’s Tree of Life initiative, in the press release.

Scientists have still not solved the mystery of how the palm is pollinated, but have discovered that its seeds are dispersed throughout the rainforest after being dug up and eaten by the bearded pig (Sus barbatus), which has a finer sense of smell than humans.

“Identifying Pinanga subterranea as new to science would not have been possible without extensive reference collections of palms in botanical institutions in Indonesia, Malaysia and at Kew, as well as decades of expertise in our team in collecting and identifying palms. This research is a reminder that we need to keep investing in both… taxonomic collections and the next generation of plant experts to allow similar mind-boggling discoveries in the future. There is so much left to discover about our increasingly threatened natural world,” Kuhnhäuser said in the press release.