Pretty but invasive: stopping monkeyflower spread

17 May 2022

#WorldBiodiversityDay An invasive weed threatening to swamp our waterways is the focus of Aaron Millar, a master’s student at the University of Canterbury.

  • Aaron Millar

    UC master’s student Aaron Millar is researching ways to stop the spread of monkeyflower, an attractive North American plant that is invading pristine areas of Canterbury and Otago.

Sustainable Development Goals 15 - Life on Land

Sustainable Development Goal (SDG) 15 - Life on Land

Colloquially known as monkeyflower, the plant is particularly prominent in Canterbury and Otago, although found throughout the country.

“It likes lots of light, so it's commonly found in farm culverts, roadside ditches, and small streams. If you're driving along in summer and see a ditch full of yellow flowers, you're probably seeing some.

“The big concern though is that it's got a foothold in some of the culverts and streams of some really pristine places such as the Lewis Pass, and in in areas around Mt Cook and Lake Tekapo,” says Millar who specialises in the evolution of invasive weeds.

“Worryingly, it’s being found in more and more remote highland areas.”

Millar says monkeyflower grows extremely thickly and can completely fill small waterways.

“This has all sorts of issues for water flow. Landowners have to dig it out if it gets too bad, and I've spoken to respective Council staff who have to try and manage it at their end too, so it's a major headache. And you don't want something that can grow so quickly getting established in natural streams, because it can drown plants we do want.”  

For his Master of Science in Biology Millar is looking at why monkeyflower is so successful in such a range of environments.

“Unfortunately, it’s one of those tenacious weeds you can just never fully get rid of, which I'm sure any gardener can relate to. But we know it hates shade so by planting things like tussocks or small trees over waterways, it can be shaded. This reduces its density by as much as 80%, which is enough to stop it clogging the waterways or causing any major problems,” he says.

Millar’s interest in monkeyflower was piqued in 2017 when helping another UC student during a summer research scholarship. They found a lot of variability between different plants in different parts of the country, and Millar wanted to see if those differences could be connected with locally important factors. He was recently awarded $9,130 from The Brian Mason Scientific & Technical Trust to help fund his work.

Monkeyflower, more formally known as Erythranthe guttata, was introduced to New Zealand by pakeha settlers in the colonial period.

Originally from North America, it was kept as a garden plant in Britain, and they liked the look of it enough to bring it here. Scotland is also fighting its invasive impact.

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