Making a mockery out of our native plants

A Victoria University of Wellington study has revealed remarkable similarities between two New Zealand plants, and shown possible use of an age-old defence mechanism previously seen only in animals.

Small toropapa (left) and horopito seedling (right)
Small toropapa (left) and horopito seedling (right)

The study compared the size, shape and pigmentation of hundreds of leaves on horopito and small toropapa plants, and found a perfect match.

“Small toropapa is often mistaken as horopito—also known as the New Zealand pepper tree,” says Karl Yager, a PhD student in Victoria’s School of Biological Sciences.

“Over a third of the leaves of the two species cannot be statistically distinguished from one another. Unless the plants are flowering or fruiting, the only fast way to tell them apart is to taste a leaf.”

Mr Yager says this exact match between horopito and small toropapa provides tantalising evidence of what is called Batesian mimicry.

“Batesian mimicry is a common evolutionary tool where unprotected species imitate harmful or poisonous species to protect themselves from predators. Because of horopito’s pungent, hot peppery taste, that leaves one with a numb tongue when a leaf is chewed, it is unpalatable to predators,” he says.

“On the other hand, the small toropapa is highly palatable and largely defenceless. It is possible that the small toropapa has evolved its leaves to resemble the horopito and confuse would-be predators.

“To date nearly all the research on mimicry comes from animals and although this research does not prove Batesian mimicry in plants, it provides the first detailed evidence consistent with Batesian mimicry.”

As small toropara were possibly eaten by moa it is likely that it evolved in response to moa domination, Mr Yager says. “Unfortunately we can't directly test this but it provides an exciting hypothesis for future studies on Batesian mimicry in plants.”

The study, published online today in Botany, was co-authored by Karl Yager and Professor Kevin Gould from Victoria University, and Dr Martin Schaefer from the University of Freiburg in Germany.