The tree species known only as Pennantia baylisiana could be the rarest plant on Earth. In fact, the Guinness Book of World Records once called it that. Just a single tree exists in the wild, on one of the Three Kings Islands off the coast of New Zealand, where it has sat, alone, since 1945. It didn't used to be so solitary, but humans introduced goats to the island, which ate every other member of its species.

Over the last few decades, scientists have tried to create more P. baylisiana trees, but aside from getting cuttings to grow, simple biology got in the way: The tree was thought to be female, and it appeared to need a male to properly generate fruit and seeds.

While preparing a recovery plan for the species in the early 1990s, Peter de Lange, a scientist with the New Zealand Department of Conservation (DoC), found several intriguing pieces of information. First, gardeners on the New Zealand mainland had several P. baylisiana seedlings (all cloned from cuttings of the original plant), which proved to be pure examples of the species, not hybrids of other Pennantia species as had originally been thought. Second, one of the seedlings had actually produced fruit following manual pollination. This led de Lange to conclude that the wild tree might not truly be female after all. Additionally, similar research published around the same time suggested that the tree was female but appeared to also bear a low level of male-like qualities that would allow it to pollinate itself.

Since then, hundreds of P. baylisiana seedlings have been sold by mainland nurseries, but scientists delayed taking trees or seeds back to Three Kings Islands for fear of introducing diseases or fungal pathogens that could harm the healthy wild tree.

But this year, de Lange and his team have returned to Three Kings Islands with the intention of planting 1,600 P. baylisiana seeds. The seeds, says de Lange, have been carefully prepared to eliminate any possibility of disease. "We removed the flesh, air-dried the seeds and then washed them in 10 percent hypochlorite and then 70 percent ethanol in a lamina flow hood. We found the seeds germinated fine with this treatment, and preliminary screening showed no evidence of virus or other diseases."

And so P. baylisiana seeds are returning to their native land, and it is hoped that new trees will soon follow. The seeds are expected to take six to 10 years to grow large enough to themselves start flowering. The project will continue until they have 500 viable adult trees.

De Lange says this stage is exciting, but there is still risk. "Of course this action does not address the fact that all seedlings are derived from one tree," he says, "so the species is severely bottlenecked," meaning it lacks the genetic diversity that could protect it in the long run from diseases and other factors. "But we have the knowledge that the species is a polyploid [has extra chromosomes], so hopefully it has plenty of resilience."

Meanwhile, de Lange reports that his colleagues have not been idle on the island. Janeen Collings, a botanist with the DoC, has planted several cuttings near the original tree, several of which have grown and, with her help, produced fruit. "While birds probably took most mature fruit, some she managed to get and sow in the field," de Lange says. Although the seedlings grew, they unfortunately died within a year. "Although this sounds unpromising, when you consider the islands are virtually inaccessible and it's expensive to get there, and to do this type of work you need to visit three to four times a year, her work is spectacular to say the least," de Lange says.

Photo: The last wild Pennantia baylisiana tree. Photo by Tony Silbery. Used with permission.