"Aotearoa is extremely diverse, stretching from the subtropical waters of the Rangitāhua/Kermadec Islands to the colder waters of the subantarctic islands. Lots of these locations, particularly the subantarctic islands, are only rarely and opportunistically explored, meaning we don’t have many samples of the seaweed and invertebrates that live in the coastal water there," said Dr D’Archino.

Seaweed provides essential habitat for fisheries and plays a vital role in carbon capture - assisting the oceans to produce about 50% of the Earth’s oxygen.

Dr D’Archino has been studying New Zealand seaweed for 20 years, collecting and identifying specimens to fill knowledge gaps and document the native flora.

So far, she has described 27 new species and 13 new genera.

"The process of describing new species of macroalgae takes significant work to ensure the specimen hasn’t already been named elsewhere. This includes comparing morphology with other known species, which relies on having fertile samples, extensive knowledge, and undertaking DNA analysis," said Dr D’Archino.

This is made even more difficult when there are so few samples with reproductive structures needed to formally describe new genera.

One of the new seaweeds that Dr D’Archino described, came from just a single collection made by European explorers in the 19th century at the Auckland Islands and identified as Callophyllis ornata.

It puzzled her for years.

"A box full of specimens in the herbarium Te Papa included red foliose algae collected in the subantarctic islands tentatively identified as C. ornata, but were morphologically different one to another, suggesting it included more species unknown to science.

"There was a lot of detective work to link recent collections with the specimen collected in 1842; I had to borrow a little fragment of the holotype stored in the Muséum National d’Histoire Naturelle, Paris (France), and compare it to specimens collected recently. It took years, but I eventually I concluded that it belongs to an endemic new genus, Motumaha and I was able to describe other two genera, Alseida and Thetisia, from the mystery box," said Dr D’Archino.

Dr D’Archino believes there could be still hundreds of species of native seaweed alone that are yet to be described, especially from remote places as the subantarctic islands and the mesophotic zone, a habitat still poorly known. Some of the taxa discovered were collected at about 100 m depth.

"The fact that we discover new species from a few opportunistic collections hints that we’ve only scratched the surface of finding out what’s living in our oceans. It would be amazing to do a targeted expedition to these places to find what else out there - there's still so much to be discovered.

"If we don’t know what there is, how do we know what to protect from environmental degradation, climate change, and biosecurity threats? And given how important these organisms are, it seems like these are knowledge gaps we should be filling," said Dr D’Archino.