What’s that weed? The biodiversity team call in reinforcements.

17 Jun 2020, 10:20 AM

It’s not every day a weed gets people excited. But when Debbie came across a pretty-looking weed in her garden, she had a feeling it was an unusual find – and she knew exactly where to take it to find out more.

Having carefully zip locked the specimen in a bag, Debbie, an NRC Online Services Officer showed photos of it to our Biodiversity Manager and in-house plant expert Lisa Forester. She recognised it as a type of Viola but checked the Plant Conservation Network website to be sure.  There was only one record of a Viola with similar leaves listed from a site in Whanganui. The details mentioned that it spread by seed, was hard to eradicate, and it was long persistent. So, after collecting some good-sized samples, it was time to call in reinforcements and confirm that Lisa had got the identification right. What was this plant?  Was it a pest? Should it stay, or should it go?


The unusual leaves that alerted to a potential pest plant

The matter was escalated to Auckland Museum Herbarium to get to the bottom of the mystery weed.  The museum has a massive collection of over 333,000 botanical specimens in a bunker-like library filling the space from floor to ceiling with collections dating back to Captain James Cook’s botanists, Joseph Banks, and Daniel Solander.

Herbarium sheets are stored in boxes, and new samples are added or recorded to a collection when they are positively identified.  Lisa has sent thousands of specimens to the Auckland Herbarium over the years, so she knew if anyone could identify the weed from Debbie’s garden, it would be them.

The mystery weed did turn out to be the species that Lisa had identified it as – an arrowhead viola (Viola betonicifolia). It’s not commonly found in Northland gardens, but it does grow here and is more than likely elsewhere having been spread around in garden soil.  Its country of origin is Australia, India, Pakistan, and Southeast Asia.  How it got to New Zealand is hard to know but, like many other weeds, it was most likely introduced because it looked pretty.  Sadly, many plants behave very differently outside their home environment.  In fact, some of the worst weeds are threatened plants in their native countries!

It was such a good find that Auckland Museum Herbarium will keep it for their collection.  They will tag it with a herbarium label, and it will be kept forever as part of their collection. From garden to archive – Debbie’s find was significant for both Northland Regional Council, Auckland Herbarium, and our knowledge of the NZ flora.

What should Debbie do with the new weed? Although it doesn’t appear to be a serious problem elsewhere in the world, it is a persistent weed in Whanganui and easily spread by seed.  Since Whanganui is the only other site where it has been recorded in NZ, Debbie should try to remove it before it spreads elsewhere.

What should we do if we spot something unusual in our garden? One of the crucial things to remember is, even if it looks pretty, it could potentially be a pest weed, and Northland Regional Council should be made aware of it. 

If you spot anything unusual, first check the pest control hub on Northland Regional Council’s website.  If it’s a known pest or you still aren’t sure – get a good specimen (or a good photograph will often do for a start) and, when bringing it for identification, try to include additional details:

  • Where was it growing?
  • What was growing near/with it?
  • Was it in a shady spot or an exposed area? (shady spots are where weeds spread, and they are an area of concern)
  • How is it spreading? Is it fruiting or flowering?
  • Your contact details so we can list you as the collector and get back to you

If the plant can’t be identified using the pest control hub, it can be escalated to the biosecurity or biodiversity team.  

Who would have thought an innocent evening of gardening would have such significance? It just goes to show, if you’re not sure, ask!


The flower of the Viola betonicifolia


It may look pretty but it's a pest plant