Plants that flower and fruit entirely below ground are exceptionally unusual. The vast majority of flowering plants (angiosperms) have evolved to develop their flowers and fruit above ground, which helps to facilitate pollination and the dispersal of seeds. But there is a small subset of plants that has evolved to flower and fruit underground – phenomena known as geoflory and geocarpy, respectively.
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What is geoflory and geocarpy?
Geoflory literally translates to “flowering in the earth”, whereas geocarpy means “fruiting in the earth”. Below-ground flowering and fruiting are at first sight a big paradox because they seem to hinder pollination and fruit dispersal. However, most geocarpic plants occur in arid or desert environments, where subterranean fruiting may help to maintain a favourable micro-environment for plant offspring and provide protection from heat and herbivory. Many variations of geoflory and geocarpy exist. In geophytic geocarpy, such as in Pauridia longituba (Hypoxidaceae), flowers are displayed above ground but the ovaries still remain below the ground. Active geocarpy occurs, for instance, in the peanut (Arachis hypogaea, Fabaceae), in which flowering occurs above ground followed by burial of the fertilised flower and fruit development below ground. In amphicarpic plants, such as Commelina benghalensis (Commelinaceae), distinct sets of flowers and fruits are developed both above and below ground. Although geoflory and geocarpy are rare, the phenomenon is widely scattered across the angiosperms.
What pollinates underground flowers?
At least 33 plant families, 89 genera and 171 species are known to flower or fruit underground, but almost all display at least part of their reproductive organs above ground. Full geoflory and geocarpy, in which plants flower and fruit exclusively below ground, are exceedingly rare but have, for example, been documented in the Australian underground orchid genus Rhizanthella. There are only a few examples of geoflory and geocarpy known from the tropics. In the palm family (Arecaceae), neither geoflory nor geocarpy has been reported until now.
A very exciting new species
We’re very excited to name a new species of palm from the tropical island of Borneo to science. Pinanga subterranea (Arecaceae) is the first member of the palm family recorded to flower and fruit almost exclusively below ground. This unusual behaviour has mystified experts as it seemingly hinders a plant’s ability to successfully pollinate and spread seeds, and it has never before been observed in the palm family. With the description of the species as new-to-science, we hope to attract the interest of other researchers who may help unravel some of the mysteries surrounding this unusual species – such as what pollinates its underground flowers? How is seed dispersal possible if they are buried underground? And how were scientists not aware of this species until now?
This highlights the need to collaborate more closely with indigenous communities
Strikingly, this remarkable species is widespread across western Borneo and valued by the local people for its edible fruits but has escaped the attention of scientists. We believe this highlights the need to collaborate more closely with indigenous communities and their intricate knowledge of the landscape and forests. Without a 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.
Tackling biodiversity loss
There are over 2,500 species of palm known to science, sadly up to half of which may be threatened with extinction. Kew experts are working with global partners around the world to identify and save species, as we may be losing more species quicker than we can find and protect them. This could have big consequences in the search for food crops that are resilient in the face of climate change and new medicines. In 2020, Kew scientists estimated in the State of the World’s Plants and Fungi report that 2 in 5 plants globally are threatened with extinction. RBG Kew scientists and partners are working around the world to name new species to science and protect areas against biodiversity loss.
In 2022, Kew experts named a total of 90 plants and 24 fungi as new-to-science, including the world's largest giant waterlily (Victoria boliviana) and a Caribbean rainforest tree (Carpotroche caceresiae) named in honour of assassinated environmentalist Berta Cáceres Flores. Identifying Pinanga subterranea 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.
Read more about the underground palm discovery