These unique trees only flower once in their life — then die

A rare natural event is underway in Darwin, with a series of Gebang palms flowering for the first time ever. (ABC News: Pete Garnish)

A group of Gebang palms, which have been growing in Darwin for decades, are flowering for the first and only time.

The trees are monocarpic, meaning they only flower once, and will die soon after dropping their fruit.

The City of Darwin will collect the seeds and plant a new generation of palms, though traditional owners are concerned wild populations are declining in Arnhem Land.

Almost two dozen decades-old palm trees, of a species rarely spotted across Australia, are currently flowering in Darwin for the first — and only — time.

Northern Territory Herbarium chief botanist Nick Cuff said the Gebang palm trees — scientific name Corypha utan — were monocarpic, meaning "they only flower once in their life".

He said the palms were "known to do what we call synchronous flowering".

In Australia, Gebang palm trees only grow in tropical wetlands. (ABC News: Michael Franchi)

"They put all of their energy into putting out this massive inflorescence of many thousands or millions of individual flowers which will bear the fruit," he said.

While Gebang palms are found throughout much of Asia, their Australian population is confined to the tropical wetlands of Arnhem Land and Cape York.

The palms boast thousands, if not millions, of individual flowers. (ABC News: Pete Garnish)

How Gebang palms came to be growing in Darwin's public gardens depends on who you ask.

Local botanical author John Brock recalls gathering samples of the plants decades ago, when he worked as a seed collector for the NT government.

He said as part of the job, he was "lucky enough to get several trips to Arnhem Land", and on one of them, he brought a piece of Arafura Swamp back to Darwin.

After the Gebang palms drop their fruit, the trees die. (ABC News: Michael Franchi)

"[In the] mid-1980s, I collected several hundred or thousands of seeds — like round golf ball nuts — and brought them back," he said.

"It's likely the ones we're seeing flowering are 30 to 40 years old, which is around the time I brought them back."

Former agricultural scientist Rob Wesley-Smith said he also had a hand in introducing the trees to Darwin.

He worked with the NT government in the 1970s, when he said he noticed a group of the palms in Darwin's botanic gardens.

Rob Wesley-Smith says he noticed one of the trees flowering shortly before Cyclone Tracy hit Darwin. (ABC News: Michael Franchi)

"One of them was huge and it was flowering just before Cyclone Tracy came, as t