In 1991, botanist Rodrigo Bernal was driving into the Tochecito River Basin, a secluded mountain canyon in Colombia, when he was seized by a sense of foreboding.

Two palm experts were with him: his wife, botanist Gloria Galeano, and Andrew Henderson, visiting from the New York Botanical Garden. They were chasing the Quindío wax palm, the tallest of the world’s palms.

Wax palms have long intrigued explorers and botanists. Until the giant sequoias of California were discovered, wax palms were believed to be the tallest trees on Earth. A thick wax coats their trunks, something not seen in other palms, and they live where palms aren’t supposed to: on the chilly slopes of the Andes, at elevations as high as 10,000 feet. This has made them notoriously hard to collect and study.

The Quindío wax palm was named Colombia’s national tree in 1985, but the distinction came with little protection. Many were marooned in pastures and vegetable fields, remnants of forests past. Wax palms cannot reproduce outside a forest: Their seedlings die in full sun, or are eaten by cows and pigs.

In Colombia’s largest known stand of the palms, only a couple of thousand remained. But the scientists had heard that there were hundreds of thousands in the Tochecito River Basin — making it the world’s biggest wax palm forest, if the rumor proved true.

But the canyon was controlled by guerrillas with the Revolutionary Armed Forces of Colombia, or FARC. As a field scientist, Bernal often found himself in lawless corners of the country. But with Henderson in the car — a foreigner, an easy target for kidnapping — the solitude became terrifying. But they had ventured far enough to see and to photograph lush stands of the palms cascading down mountaintops.

Bernal decided that if he couldn’t study Tochecito’s palms, he would have to forget them. To the scientists’ surprise, they were able to return in 2012, after the army had driven out the FARC. In the guerrillas’ absence, they found, the last giant stands of wax palms faced new and dire threats. Now Bernal and his colleagues are trying to save the palms, and study them at the same time.

By the time Tochecito became safe to visit again, the scientists had a new collaborator: María José Sanín, now a botanist at CES University in Medellín. Most of what is known about wax palms comes from Bernal, Galeano and Sanín. Galeano died of cancer in 2016; since then, the research team, once a trio, has mainly been a duo.

For all Bernal and Sanín have contributed to the science of wax palms, conserving them remains elusive.

Colombia’s only established wax palm sanctuary lies near Jardín. It is run by a group that aims to protect the endangered yellow-eared parrot, which nests in wax palm stems. The problem is, the palms must be dead.

In 2012, the scientists mounted an effort to protect 2,000 wax palms near Salento, but there is also heavy cattle grazing and the constant threat of mining there.

They turned their efforts to the newly accessible Tochecito, which had about half a million palms growing on private land, and fewer owners to win over.

In 2016, Bernal and Sanín proposed a government-backed palm sanctuary that would protect the entire 32 square miles of the river basin. But after 18 months of “meetings in Bogotá, meetings with proprietors, meetings with the ministry of the environment,” Bernal said, most of the landowners walked away.

Bernal said he believes that the best hope lies in land purchases to create a contiguous chain of sanctuaries. Just two large tracts harbor a quarter of the palms, he said. With four, most of the forest could be saved.

He stopped his car briefly at the base of the valley, where the FARC encampment used to stand. There was virtually nothing left of it, just remnants of a garden the guerrillas once maintained, in a clearing they’d used as their dance hall.