28 June 2023

The palm that flowers underground

A new species discovery hosts one of the rarest and most unusual traits seen in plant life.

Sebastian Kettley pic
A headshot of Ben Evans

By Sebastian Kettley and Ben Evans

Mature and immature fruits poke out of soil that has been dug away.

Kuching, Malaysian Borneo. Veteran palm researchers John Dransfield, a Kew Honorary Research Associate and Paul Chai, a Malaysian botanist, are beginning the day at their favourite morning dining spot. 

Across the table are budding Kew PhD students, Ben Kuhnhäuser and Peter Petoe, aspiring palm experts at the beginning of a 7-week expedition to Borneo. Their goal, to collect as many palm species as possible, contributing to an epic international effort to build the palm tree of life. 

Paul regales the trio with a memory from years long past. 

“Back in 1997 I was in Lanjak Entimau Wildlife Sanctuary in the heart of Borneo. I found this beautiful young palm, and in an attempt to get a better look, I was brushing aside the thick leaf litter surrounding it. I stumbled across the plant’s fruit just hidden a few centimetres below the surface. Do some digging if you’re heading out that way”.

Days later, after an adventure featuring multiple drives, a longboat river voyage and hours of hiking, Ben and Peter are deep in the forests of Lanjak Entimau. They’re joined by Kew Senior Research Leader and palm expert, Bill Baker, as well as Sirukit anak Dubod from the Sarawak Forestry Corporation and local guides from Nanga Talong, without whom the expedition would not have been possible.

Making a stop, the team begin digging through the soil at the base of a young palm matching the description given by Paul. At first, nothing out of the ordinary, it looks just like an unremarkable palm seedling.

Some inches into the dirt however, structures start to emerge – an entire cluster of fruit, a stem and a crownshaft (the base of the leaves on palm plants), all buried in the soil. The entire reproductive structure existing below the surface means that the flowers are underground too. Highly unusual, even here in this place of great natural diversity. 

Longboat pilots hold huge bamboo poles to stabilise their boat in the white waters of a river.
The research team's journey to Lanjak Entimau included a longboat voyage down turbulent river waters. © William J. Baker, RBG Kew
Two researchers sit next to a palm plant nestled into the soil. The exposed underground area shows fruit.
A startling find, Dr William Baker and Peter Petoe take a moment to pose with a plant that would later be named P. subterranea, a new species © Ben Kuhnhaeuser, RBG Kew

In parallel, the plant had independently been found by Indonesian botanist Agusti Randi, based at the National University of Singapore. In the forests of West Kalimantan, Indonesian Borneo, he’d discovered a group of wild boar unearthing red fruit at the base of otherwise ordinary looking young palms. 

A palm plant that flowers and fruits entirely underground – a new species Pinanga subterranea. Why adopt this underground lifestyle, and if it’s so unusual, why didn’t science know about it already?

Green and brown cone-shapped fruit protrude from a palm stem
A closeup of P. subterranea's undeveloped fruits, emerging as green and brown structures from the sub-surface region of the palm. © Agusti Randi

Why would you ever need to flower and fruit underground?

This is an especially valid question as exclusively flowering and fruiting below ground really is incredibly rare.

Only one genus is known to do this, Rhizanthella, a group of underground orchids who obtain their entire survival needs through a symbiotic relationship with fungi. 

Pinanga subterranea doesn’t have a fully underground life like Rhizanthella. The leaves it sends above for photosynthesis makes it look just like the many other palms that grow without a stem at ground level. 

If it’s not hidden completely, then what benefits does it bring to hide your flowers and fruits from the surface? 

Widely known benefits of underground fruiting and flowering are protection from surface predators and ensuring that a plant’s offspring grow up in the exactly the right conditions they need to survive. 

The real problem for a plant, is how to disperse pollen underground. 

It's possible that insects with an underground lifestyle carry pollen from one palm plant’s flowers to another, but for now, the true mechanism of pollination remains a mystery to us.  

Randi’s experience with wild boar munching on unearthed palm fruit provides a potential answer to the question of fruit dispersal, however. In fact, seeds of P. subterranea have been found in wild boar dung and successfully germinated from it, but a full study is yet needed to investigate this relationship in full. It’ll be some time yet, before these ideas form answers. 

A pig is black all over with much longer hair around its chin and neck, giving it its "bearded" title
Bornean suids such as this bearded pig are so far the most likely seed dispersers of the underground palm © Ben Kuhnhaeuser, RBG Kew
A column of developing fruits appear as yellow cylinders stacked atop each other in a single column
Dug out from the soil, a developing cluster of P. subterranea fruits are clear to see © William J. Baker, RBG Kew

Defining discovery 

Some 300 species of palm (family Arecaceae) are known to science on Borneo, one of Earth’s most biodiverse places. In particular, the palm genus Pinanga contains many species found nowhere else other than Borneo, and new species have continued to be described in recent decades. 

To declare this underground palm a new species to science, Agusti Randi first made comparisons of this new palm to all other known Pinanga palms, a massive undertaking. For this, the team leant on the reference plant collections built by decades of botanical study at institutions in Malaysia, Indonesia, as well as Kew. 

The key term here is a new species to science. Rarely is it that plants found by scientists are completely new to humanity. 

At the time the hidden features of this particular palm were being uncovered by the research team, the plant had at least four names in at least three Bornean languages: Pinang Tanah in Malay, Tudong Pelandok in Iban, and Pinang Pipit or Murina Pelandok in Kendorih. In some Indonesian communities the fruits dug up by Paul Chai in the 90s have been a known food resource for generations. 

Better interaction between science and the wealth of wildlife knowledge held by communities and indigenous groups holds huge potential for new scientific discoveries that might benefit people everywhere.

Red fruits about a centimetre in size are lined up for examination
P. subterranea's fruit once ripened turn red in colour. They're known to be used by some Indonesian communities. © Agusti Randi

Science in the deep and dark

A new species and a fascinating new mechanism of plant life aside, this research journey is a key reminder of the knowledge that’s still out there right under our noses. This species has been hidden in plain sight in untapped cultural knowledge, and physically in the soil below our feet.

We often think of outer space or the ocean depths as the frontiers of modern exploration, and yet there’s still so much we don’t know about the world beneath us. 

These underground unknowns include species like P. subterranea that may play a key role in increasingly fragile ecosystems. They also include the interactions between plants and mycorrhizal fungi that, through carbon storage, may be doing a huge and uncredited amount of work in keeping our climate stable. 

Only by looking beyond what we can see with our eyes will we find new knowledge, the taxonomic building blocks that allow us to protect this wonderful, bizarre natural world. 

A landscape view shows forested hilltops emerging from low-lying cloud sitting in the valleys
The forests of Borneo remain vast despite deforestation. Who knows what discoveries might lie below the surface of the soil. © Ben Kuhnhaeuser, RBG Kew
A researcher removes soil from the base of a palm, exposing small fruits

Read the full open access publication

Hiding in plain sight: The underground palm Pinanga subterranea

Two researchers sit next to a palm plant nestled into the soil. The exposed underground area shows fruit.

See a fully-illustrated species description

Pinanga subterranea, a New Arecoid Palm from Borneo that Flowers Underground

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