How did mistletoe get into the treetops?

It is not clear who was the first trendsetter who hung the mistletoe. Some blame the ancient Greeks, who kissed under the plants during harvest festivals. Others attribute this to the druids of the first century, who could have decorated their houses with them for luck.

But we may have to look further back. An article published in The American Naturalist this month features new potential culprits: tiny prehistoric and marsupial primates, which may have brought plants – or at least their seeds – to the top of the forest tops more than 55 million years ago .

Almost all the mistletoe species in the world live on the branches of trees or shrubs, where they gather in their hosts through root-like structures and drain water and minerals. They use the energy they can to grow colorful and showy flowers and to drop nutritious leaves with abandon.

You can call it parasitism – but you can also call it being the life of the party. Well-trimmed mistletoe plants attract a host of creatures, from bees and other insects that pollinate their flowers, to mammals and birds that live on their branches. They are “the center of attention in many terrestrial systems,” said David Watson, professor of ecology at Charles Sturt University in New South Wales, Australia and author of the new article.

Songbirds like to stuff themselves with mistletoe berries. Prehistoric songbirds are believed to have helped mistletoes to travel the world and land on different types of hosts, where they eventually diversified into the hundreds of species that exist today. The hypothesis was also raised that songbirds helped a vital stage in the evolution of mistletoe: the movement of the soil – where the mistletoe ancestors parasitized the roots of other plants – to the tops of the trees, where they hit the branches.

But a recent analysis of the evolution of mistletoe has complicated this story. This delayed the date of this crucial move further back than previously thought, to the 55 million-year-old band – long before any of the groups of songbirds that now depend on mistletoe first appeared, Watson said.

“It reminded me that, well, there are other organisms out there now, that eat mistletoe,” he said. Perhaps one of them had an ancestor who carried a fateful berry to the top of the trees.

Dr. Watson, who spent decades studying mistletoe in many environments, flipped through his mental Rolodex from contemporary dispersers.

A hamster-sized marsupial, the Monito del monte, came to mind. The species is the only mistletoe disperser in the Andes, he said. “If you see a mistletoe in the Andes, it came out from the rear” of a Monito. The ancestors of this animal were well positioned in space and time to enjoy the fruits of an ancestor of contemporary mistletoes and celebrate nearby trees with the resulting droppings.

Other small climbers, the rat lemurs of Madagascar, spread a different type of mistletoe through their own ritual. Their local mistletoes have small, sticky seeds. Lemurs “keep the seeds attached to them and clean them as a family,” said Watson. Their ancestors – or another primate from the past – may have inadvertently done something similar, starting a new era of mistletoe.

It is almost impossible to know for sure. The scenarios Watson presents from canopy-driven mammal movements are “plausible, but not the only ones,” said Romina Vidal-Russell, a botanist at the National University of Comahue in Rio Negro, Argentina, who specializes in plant parasites. Some fruit-eating birds were also around at the right time, she said, and may have helped the plants make the leap.

“Unfortunately we don’t have a time machine to go back and see,” said Vidal-Russell.

No matter who was involved, it must have been a festive scene.