Plant collectors have searched for the hidden wonders of the plant world for centuries.

Yet plants that are new to science are still being described, at a rate of about 2,000 a year.

Scientists at the Royal Botanic Gardens, Kew, discovered and named more than 100 new plants in 2018.

Their list of the top new plants includes carnivorous pitcher plants, exotic orchids and climbers with untapped medicinal powers.

Herb found in a waterfall
Prof Aiah Lebbie discovered an unusual plant clinging to rocks near a water fall in Sierra Leone. He collected a specimen and sent it to Kew, where it was identified as a new species. The plant, Lebbiea Grandiflora, has been named after him.

"It's got unique characteristics, that are unlike any other plant in that particular family and that straight away indicated to me that we had come across something very unique," he told BBC News. "My name will forever be linked to it."

The plant has been classed as critically endangered. Found in an area that is under threat from mining and a hydro-electric project, the scientists believe it may be extinct within a few years.

It is thought that fish feed on the plants, strengthening the health of the ecosystem.

"Every single species of plant on earth is also important for our survival," said Prof Lebbie, of the National Herbarium of Sierra Leone.

"If we say we are not going to be custodians or guardians of it and allow them to disappear, for me that is something the world has lost, and as of now we don't even know the value of it."

Bug-eater from a remote island
There are more than 150 species of pitcher plant in the world. This new discovery, Nepenthes biak, only grows on the small island of Biak, off the north coast of Indonesian New Guinea.

It is threatened by tourism when ships stop at the island. "It's known that the plant has been hunted to be dug up from the wild for sale to passing tourists," said Kew botanist, Dr Martin Cheek. "Unless something is done about protecting this species it's heading for extinction."

It is our job to protect these plants for future generations to appreciate, he said. Pitcher plants, known as Nepenthes, have a number of potential uses in medicine, which have yet to be fully explored.

They are finding new things in plants all the time, Lara Jewitt, nurseries manager at Kew, said. "We never know what we are going to discover within these plants."

Flower that could be a future cancer medicine
The new plant, named Kindia gangan, is a member of the coffee family. Kew scientists on a field trip spotted it growing on sandstone cliffs near the town of Kindia in Guinea in West Africa.

Biological extracts suggest the plant may have medicinal applications, perhaps even anti-cancer properties.

Orchid on sale after being smuggled out of the wild
A spectacular orchid was found being sold off the back of a barrow in Vientiane, the capital of Laos. The slipper orchid, Paphiopedilum papilio-laoticus, is gravely endangered.

Yam identified from an old photo
The climbing yam - a food crop in many parts of the world - was initially seen in a photograph sent to Kew in 2002. More than a decade later, pressed, dried specimens in Kew's herbarium were found to be a match.

The purple-flowered plant, Dioscorea hurteri, is found in six locations in KwaZulu-Natal in South Africa. It is classed as vulnerable to extinction.

Vibrant flowering plant from Vietnam
This brand new species, Oreocharis tribracteata, was seen on an expedition to northern Vietnam. It was subsequently grown in the UK.

Tree from the rainforest
This large tree was seen growing in a rainforest in Guinea, West Africa. In the spring it has shocking pink flowers. Talbotiella cheekii was unknown to science until 2015.

Wild spice tree
This tree, Pimenta berciliae, is related to the tree that brings us Allspice, a vital ingredient in food and beauty products.

Flowering plant from the cloud forest
This plant with pink flowers was found in a valley in Bolivia.

Tree feared extinct
One tree from Cameroon, Vepris bali, is known to grow only in a forest reserve in the Bamenda Highlands. It is thought to be extinct already due to habitat destruction.