New species of palm found to flower and fruit underground

A unique palm species is giving scientists new insight into the plant world.

The newly described Pinanga subterranean, named for its partial underground lifestyle, is the only known member of the palm family (Arecaceae) to flower and fruit almost entirely below ground.

While P. subterranean was already well-known in its native Borneo among local communities who snacked on its bright red fruits, it has only recently caught the attention of the scientific community.

Researchers are now looking to understand more about this extraordinary plant, including how its subterranean lifestyle evolved in palms, how its seeds are dispersed and what pollinates its underground flowers.

Dr Norbert Holstein, a botanist at the Museum who was not involved in the study, says, ‘This newly described species highlights the importance of careful observation, the need to take time to look carefully at structures and try to understand what they do.’

‘It also shows us the importance of collaboration and not least collaboration between scientists and peoples who have different ways of understanding the natural world if we are to better understand the remarkable diversity of plants – of which perhaps a fifth remains unknown to science.’

The description of P. subterranean was published in the journal Palms, with added commentary in Plants, People, Planet.

Why do plants flower and fruit underground?

Most flowing plants develop their flowers and fruits above ground to facilitate pollination and seed dispersal. But a few select plants have evolved these traits below the soil’s surface.

Instances where flowering and fruiting occur underground – known as geoflory and geocarpy, respectively – have been observed in at least 171 species across 33 different plant families.

Most of these plants tend to display just one of these traits. For example, the peanut displays its flowers above ground but develops fruit underground. P. subterranean is exceptionally rare as it displays both geoflory and geocarpy. The only other plants known to do this are a genus of small orchids called Rhizanthella.

Unlike P. subterranean, however, Rhizanthella has a fully underground life and survives through a symbiotic relationship with fungi. But P. subterranean produces leaves above ground, so processes like photosynthesis are still taking place.

Developing fruit and flowers underground provides the benefit of protection from surface predators, but at the same time this would seemingly hinder access from pollinators and animals that could disperse seeds away from the parent plant.

Other plants in the Pinanga genus are typically pollinated by insects, such as bees, which would be unable to access the plants as easily underground.

Dr William Baker, Senior Research Leader at Kew, says, ‘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?’

Scientists have suggested that insects with an underground lifestyle could potentially carry pollen from one palm to another, but the true mechanism of pollination remains to be determined.

Wild boar have also been observed munching on the fruits of P. subterranean, which could provide an answer to how the seeds disperse. But a complete study is yet to be done to test this relationship.

Hiding in plain sight

Although P. subterranean is widespread across western Borneo and valued as a food source by local communities, it has managed to escape the attention of scientists until now.

Prior to its scientific description, the plant was known in at least three Bornean languages under the names Pinang Tanah, Pinang Pipit, Muring Pelandok, and Tudong Pelandok.

Kew scientists were first alerted to the plant’s existence by Malaysian botanist and co-author of the study Dr Paul Cha, who encountered the palm in 1997 when visiting the Lanjak Entimau Wildlife Sanctuary. Then in 2017, an Indonesian researcher and lead author of the study Agusti Randi independently encountered a couple of specimens of the palm in Kalimantan.

Eventually in 2018, a team of scientists visited Lanjak Entimau during an expedition specifically to study Borneo’s palm species, while keeping a keen eye out for the mysterious plant.

Dr Benedikt Kuhnhäuser, Future Leader Fellow at Kew, says, ‘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 and the very first known example of its kind in the entire palm family. It truly is a once-in-a-lifetime discovery.’