What can kōwhai tell us about the location of New Zealand’s forests during the ice ages?

Science researcher Lara Shepherd explores kōwhai trees, one of New Zealand’s most widely recognised native plants and our unofficial national flower.

Did you realise that we actually have eight species of kōwhai in New Zealand? Our DNA research investigating the relationships of these kōwhai species and where kōwhai trees were located during the ice ages has just been published.

Woman collects leaves from a flower-laded large-leaved kōwhai

A flower-laded large-leaved kōwhai (Sophora tetraptera) from the Wairarapa. Photograph by Leon Perrie

How are New Zealand kōwhai species related to each other?

Our genetic results show that kōwhai species share DNA with each other. This sharing of DNA likely occurs through hybridisation between the species and makes it difficult to construct a family tree of relationships for kōwhai. Prostrate kōwhai is the only species we were able to distinguish with the DNA markers we used.

Woman collects genetic samples from prostrate kōwhai

Collecting genetic samples from prostrate kōwhai (Sophora prostrata) on the Port Hills. This species is restricted to the eastern South Island and has zig-zag branches with small leaves and flowers. Photograph by Leon Perrie

Where were kōwhai trees found during the most recent cold spell of the ice ages?

Using our DNA results we were able to tell that Sophora survived the Last Glacial Maximum of the ice-age (~30,000 years ago) throughout much of the country, rather than being restricted to only a few refugia in the warmer places. This result is consistent with our past studies of the other lowland plants fierce lancewood and Hooker’s spleenwort.

The widespread survival of New Zealand lowland plants contrasts with Europe and North America, where the climate during the Last Glacial Maximum was so severe that many species had to retreat hundreds of kilometres to warmer refugial areas.

A close-up of Cook Strait kōwhai

Cook Strait kōwhai (Sophora molloyii) . This species is naturally uncommon in the wild where it is restricted to coastal areas on both sides of Cook Strait. It is a popular garden plant and is often sold as Sophora cv. Dragon’s gold. Photograph by Leon Perrie

6 Responses

  1. Andy Blick

    Interesting research. I live in Minginui, in the Whirinaki forest. There a several large groves of kowhai here that I think were possibly planted by Maori in order to harvest tui when flowering occurs. Tui converge on these groves in their hundreds.
    I have also noted an association between kowhai and totara. Quite a few totara trees (nitrogen demanding)have kowhai trees (nitrogen producing) growing around them.
    In years of wandering in this forest I have only found one microphylla with long hanging branches.
    Whirinaki kowhai flower in late September early October which seems to be later than other places.
    While checking kowhaI just last week, I noted nearly each tree had a quietly sitting kereru. These kereru are eating the leaf as there is no forest fruits at this time of year.
    One question I wonder about is how is kowhai seed dispersed and how does its hard cover get broken down? Seeds often seem to last for years under the tree without apparent change.
    Thanks again for putting up your kowhai research results.

    Reply
    • Lara Shepherd

      Hi Andy,
      Thank for you interesting comments. It is very possible that kōwhai was planted in Whirinaki to attract birds to be hunted. Sophora microphylla is fairly uncommon in Northland so you might be seeing Sophora chathamica instead (according to the NZPCN website it flowers from August to November).

      Kōwhai seeds float really well and are dispersed by water (both fresh and seawater). But this doesn’t explain the trees that grow away from water. Seabirds sometimes swallow the floating seeds then regurgitate them, which may explain some of the inland seeds. Also kōwhai pods, with the seeds inside, can be moved short distances by wind.

      You are correct in stating the seeds last for years – one study was able to germinate seeds that had been in storage for 40 years! It has been suggested that the seed coat gets broken down by microbes, or other organisms, in the soil allowing water in so the seed can germinate. This is just a hypothesis though as it isn’t known for sure.

  2. Jenny Hartley

    Hi Lara, I am currently in discussions about leaving some Renga renga in Tawatawa Reserve which is in Owhiro Bay. Celia Wade Brown has had a bench put in the reserve to commemorate her mayrolty. Her kind friend planted some Renga renga around it. Our Group Southern Environmental Ass. of which I am the chair has an MOU with the council to plant only eco-sourced plants. We take this very seriously. Is the Renga renga likely to be endemic, or is more likely to be brought here by Maori, or have we entered a very grey area. Celia has kindly said we can put in something else. But it is very interesting, (we have stopped planting Ake ake because of concerns). Looking froward to your reply to throw some light in,

    Cheers
    Jenny Hartley

    Reply
    • Lara Shepherd

      Hi Jenny,
      Rengarenga isn’t endemic to the Wellington region but plants that were moved here by Maori in pre-European times would have some historic value. However, rengarenga currently grown in Wellington in people’s gardens and sold in garden centres may have come from anywhere within rengarenga’s range and aren’t necessarily related to the plants that were moved by Maori (which were introduced to Wellington from the eastern Bay of Plenty/East Cape region). I’m hoping to do some more work in Wellington to determine the source of the plants being grown in gardens, as well as plants that may be garden escapees (=weeds) or may be remnants from Maori gardens. If you can get me a piece of leaf from a couple of your plants I can see if I can determine their source.
      Cheers,
      Lara

  3. Robin Watt

    What a good piece of research. Well done. Now: I cannot access the publication using the link above so (a) did the research reveal (or could it be used to) any indication that any kowhai was spread by Maori in prehistoric times? (b) did the research consider that any kowhai, or some subspecies of it, could have been brought to NZ by prehistoric Polynesian settlers? (c) is there any indication from the research that founder populations together with isolation (perhaps in conjunction with ‘a’ and ‘b’ above) accounted for differences in their respective DNA profiles? Thanks, Robin.

    Reply
    • Lara Shepherd

      Thank you Robin. I’m going to write another blog shortly about coastal kōwhai – the populations of this species around Wellington and on the Chatham Islands have been suggested to result from Māori plantings.

      We have done another study looking at the relationships of kōwhai around the Southern Hemisphere and we found that kōwhai species on Pacific Islands differ genetically from the species in New Zealand so we can rule out an human introduction to New Zealand from Polynesia. We’ve just submitted this research for publication and I will write a blog on the results when it is published.

      In answer to your last question I think isolation has had a big part in the genetic patterns we see in New Zealand kōwhai. Many parts of New Zealand have unique DNA sequences and these have likely evolved in isolation. Interestingly these regional DNA types are often shared between different species. For example, there is a DNA type only found in the Wairarapa but it occurs on both Sophora tetraptera and Sophora microphylla.
      I hope this answers your questions!

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