Speargrasses are some of Aotearoa New Zealand’s most distinctive plants and an iconic feature of many of Te Waipounamu’s non-forested habitats, especially when flowering. Te Papa Research Scientist Lara Shepherd and Botany Curator Leon Perrie analysed DNA from speargrasses to examine how genetic diversity is partitioned across Te Waipounamu South Island. The results revealed a surprisingly complex story about how speargrasses survived the ice ages.
Speargrass/taramea (Aciphylla) is a genus of flowering plants in the carrot family. New Zealand is the centre of diversity with 36 endemic species, many of which are known for their ferocious spiky leaves.
We have a long-term research programme revising the taxonomy of speargrasses, in particular determining whether some of the tag-named entities should be recognised as new species. An important part of this revision involves using DNA to understand the relationships between speargrasses. Our initial genetic testing trialled chloroplast DNA, which we have successfully used to distinguish other plant species and determine their relationships.
A tangled family tree
Our chloroplast DNA sequencing covered samples of speargrasses and their close relatives from across Te Waipounamu South Island. What we found was far from a neat, tidy family tree.
Instead of each genus and species forming its own distinct genetic group, the chloroplast data showed a web of shared genetic variants. Speargrass species shared chloroplast variants, and there was even sharing of these variants between speargrasses and Anisotome. This pattern points to chloroplast introgression, where hybridisation facilitates chloroplasts to move between species.
Surviving the ice ages – everywhere
One of the most striking findings is how much genetic diversity is spread across Te Waipounamu South Island. High chloroplast diversity and many region‑specific DNA variants suggest that speargrasses didn’t retreat to a few isolated refuges during the last glacial maximum, when ice covered around 30% of the island. Instead, they appear to have survived in place across much of the island, even in the mountainous central South Island – an area long thought to have been too heavily glaciated for many plants to persist.
Even more intriguing, genetic variants found growing side by side today were often not each other’s closest relatives, hinting that multiple ancient lineages survived repeated glacial cycles without being wiped out.
Hybridisation as a lifeline
The study suggests that hybridisation among multiple co‑occurring species may have helped preserve this deep genetic diversity. Introgression among species, including the exchange of chloroplasts, effectively created a shared reservoir of genetic variation, allowing more variation to persist even as climate fluctuations forced species to move, shrink, or expand their ranges.
Why it matters
This research reshapes our understanding of how New Zealand’s alpine and subalpine plants endured past climate upheavals. Rather than being pushed into a few safe havens, speargrasses appear to have been remarkably resilient, surviving across a broad landscape and maintaining significant genetic diversity.
What about resolving speargrass taxonomy?
Although the type of DNA we used for this study (chloroplast DNA) wasn’t useful for our original goal of determining the relationships of speargrass species, our subsequent testing has found a DNA technique more suited to this question. We have now used this method to identify species and their hybrids as well as describe a new species – look out for a post about this soon.
Other speargrass blog posts
- An introduction to speargrasses – plants with a prickly reputation
- Speargrass collecting – a whirlwind tour of Te Waipounamu South Island
- Getting through speargrass defences: how to safely collect samples of a dangerous plant
To request pdf files of our papers on speargrasses, email us at lara.shepherd@tepapa.govt.nz or leon.perrie@tepapa.govt.nz
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