Above the forest floor: how rare are orchids in the wild?

PhD researcher Vida Svahnström takes us into the hidden world of epiphytes, why they matter for the tree-dwelling houseplants we know and love, and how we can help close a gap in conservation

By Vida Svahnström , Miguel Arredondo Uribe and Natasha Ward

Epiphytic ferns covering a branch of a tree

The first time Vida Svahnström stepped into a tropical rainforest, she wasn’t yet a fully-fledged scientist.

As a young naturalist on a field course in northeastern Australia, she spotted a hidden world stretched across the bark of a fallen tree. This world, usually suspended high above the forest floor, was made up of blankets of ferns and clusters of orchids - a miniature forest growing entirely without soil.

It was her first glimpse into the secretive life of epiphytes, and it would shape her early research career. Today, Vida is the lead author of a major study here at Kew, that flips a long-standing botanical assumption on its head.

Cyrtopodium punctatum on top of a fallen branch in a forest. — *Cyrtopodium punctatum* on top of a fallen branch in a forest. Image credit - Vida Svahnström.

Life without soil

If you’ve ever kept a moth orchid (Phalaenopsis) on your windowsill or tried growing an air plant (Tillandsia) at home, then you’ve already met an epiphyte. These are plants that grow on other plants, usually on trees. They do this not to steal nutrients from their hosts, but to escape competition with other plants on the ground.

Epiphytes perch on bark or nestle among branches, drawing moisture from rain and fog. Think of them as aerial specialists that make a living in the treetops, without ever having to touch the ground. 

They might look like parasites, but they aren’t. They don’t harm (or benefit) their host in any way. Some, like bromeliads (Bromeliaceae), can support entire microcosms; frogs, insects, and even crabs have been found living in the tiny rainwater pools inside the rosettes created by these plants’ overlapping leaves. The canopy holds an entire world of its own. 

A person in a swamp surrounded by Cypresses. — Vida Svahnström at Big Cypress National Preserve, Florida, surrounded by many epiphytes growing on the trees. Image credit - Vida Svahnström.

The myth that got in the way

For over a century, scientists assumed that epiphytes had a tendency to be widespread because of their remarkable dispersal abilities. Some, like orchids, have tiny, dust-like seeds that travel easily on the wind. Others, including members of the Aracea family like the much-loved Philodendron, Monstera, and Anthurium, have fleshy fruits that are dispersed by birds.

But data from studies on regional biodiversity and flowering plants were telling a different story. In many parts of the world, epiphytes appeared to be far less common than expected based on their supposed dispersal ability. So Vida and her colleagues decided to test the ‘widespread’ assumption at a global scale.

Approximately two thousand orchid seeds spread out next to a 20p coin that takes up half the frame, dwarfed by its size. — Orchid seeds’ tiny size - Pablo Gómez Barreiro © RBG Kew

They compiled a dataset for hundreds of thousands of flowering plant species and compared the geographic range sizes of epiphytes with those of terrestrial ground-dwelling plants. Our scientists looked at how many countries each species had been recorded in, how large an area they occur in, and how often they appeared in specimen collections (pressed plant samples stored in herbaria and used to study biodiversity over time). 

Across every measure, epiphytes came out as having smaller ranges, on average, than terrestrial plants. Far from being widespread, they tend to be range-restricted.

Dendrobium jonesii on a tree branch. — *Dendrobium* jonesii growing on a tree. Image credit - Vida Svahnström.

Rarity runs in the family

Interestingly, the story does not end with epiphytes. Their close relatives, including many lithophytes (plants that grow on rocks) also tend to have small ranges. The same is true for ground-dwelling species that belong to plant families with a higher proportion of epiphytes than others. Even these relatives, which don’t grow on trees themselves, often have surprisingly small ranges.

What links these plants is not only how they grow, but how they are related. Belonging to an epiphyte-rich family appears to be a strong predictor of rarity, even if the plant does not grow on trees. Rarity, in these cases, seems to be passed down through evolutionary lineages.

UK native orchid Orchis purpurea on a grassy field — UK native orchid *Orchis purpurea* on a grassy field. Image credit - Vida Svahnström.

Flowered Neotinea ustulata on the grass. — UK native orchid *Neotinea ustulata* on a grassy field. Image credit - Vida Svahnström.

This changes how we think about conservation. It’s not just about the plant’s lifestyle, but its evolutionary history. 

Why does this matter? Typically, conservationists and policymakers prioritise species that are threatened, or predicted to be threatened, for conservation action. This doesn’t usually include those with large ranges, since widely dispersed species are assumed to be at lower risk. But if the ranges of epiphytes and their close relatives have been overestimated, their need for conservation attention may have been underestimated at the same time.

Bromeliads on top of branches of a tree. — Bromeliads on top of branches of a tree in Jamaica. Image credit - Vida Svahnström.

Fragile specialists

Many epiphytes are specialists. They need specific microclimates, high humidity, and stable forest ecosystems to survive. These habitats: tropical cloud forests, montane woodlands, and rocky outcrops, are increasingly under threat from deforestation, land-use change and climate impacts.

When forest structure is lost, epiphytes do not just lose their support, they lose the niche they are adapted to. And because many grow only in narrow elevation zones or small areas, habitat loss can have devastating implications for their survival.

Tillandsia bulbosa on a trunk of a tree. — Close up of a *Tillandsia bulbosa* growing on a tree trunk, Jamaica. Image credit - Vida Svahnström.

Hidden in plain sight

The IUCN Red List of Threatened Species is a global register which classifies plants, animals, and fungi by their risk of extinction, but it doesn’t yet cover every species on Earth. Fewer than ten percent of all known epiphyte species have had their extinction risk assessed for the IUCN Red List. That means that we don’t know the conservation status of the majority of epiphytes.

This lack of visibility limits conservation action. When species are not assessed, they are less likely to be included in protective legislation, funding calls or habitat restoration efforts. Without recognition, our ability to protect these plants is severely hampered.   

And yet, epiphytes are some of the most visible plants in the world. Many of us grow them in our own homes - orchids, bromeliads, ferns - often without realising their wild counterparts may be under threat. Going forward, perhaps the love that people feel for their favourite houseplants can be used to help improve understanding of their fragile status in the wild.

An orchid in a home, with a cat in the background — Orchids are very popular houseplants. © Natasha Ward, RBG Kew.

Conservation with foresight

This research does more than correct a scientific myth. It gives us a chance to act early. If whole groups of plants, not just individual species, are likely to have small ranges and narrow ecological needs, then conservation prioritisation can begin sooner, not just when extinction risk becomes urgent. 

In the face of accelerating threats, we could start protecting the groups most likely to need help. To prevent the extinction of epiphytes, we need to protect their habitats before they vanish. This might include increasing funding for epiphyte conservation, raising their profile in policy discussions, scaling up protection of their natural habitats, and safeguarding species in seed banks and living collections.

Flowers of a Trichoncentrum undalatum. — Flowers of a *Trichoncentrum undalatum*. Image credit - Vida Svahnström.

Different epiphytic species covering a tree trunk. Image credit - Vida Svahnström.

At Kew, the Conservation Assessment and Analysis team, alongside projects including the Millennium Seed Bank Partnership and the digitisation project, are already laying the groundwork. But data alone is not enough. Awareness, connection, and care must follow.

Because even the most extraordinary plants can be missed, especially when they’re growing above our heads. 

Tillandsia fasciculata flowering on a tree trunk.

What can you do?

Start by seeing your houseplants differently. Every orchid or air plant could be a glimpse into a disappearing world. You can also learn more about our research by reading Vida's paper:

Geographic range size and rarity of epiphytic flowering plants