Meet the ancestors: tracing the lineage of extinct plants using ancient DNA techniques

“I was lamenting the fact centuries old plant material from some extinct species was too degraded to collect any meaningful DNA that would confirm family relationships, and Dr Jamie Wood suggested we try and use ancient DNA methodologies instead,” says Peter.

The approach was successful, and Peter and Jamie were able to show the now extinct Streblorrhiza found on Phillip Island, off Australia’s southern coast and collected by a botanist called Ferdinand Bower in 1836, was in fact related to New Zealand’s native brooms (Carmichaelia).

If the process worked once, Peter and Jamie reasoned, it should work again. “We had a sample in the Allan Herbarium of Logania depressa, a now extinct diminutive plant that has only been collected once, from the central North Island, by William Colenso in 1847,” Peter says. “We just never knew if this plant was the only New Zealand member of the Logania genus, of which there are 24 species in Australia.”

Logania depressa Hook.f., collected 22 February 1847, Ruahine Mountains; [Given by WRB Oliver, in N.Z. J. Sci. Tech. 4 (1921): 263, as "east of Waiouru and north of Moawhango Township"], New Zealand. Acquisition history unknown. CC BY 4.0. Te Papa (SP004635)

An ancient DNA laboratory, physically isolated from other molecular laboratories at Manaaki Whenua’s Lincoln site, was purpose-built and genomic DNA was extracted from leaf fragments.

“While the relationship with the Australian genus remains unresolved,” says Peter, “the results show using ancient DNA processes and methods does work to study old plant samples.”

Another two specimens from extinct plants have headed into the ancient DNA lab, with impressive results.

“There is a story that a tree grown from a seed collected from the last remaining Sophora toromiro on Rapa Nui (Easter Island) was planted in Christchurch’s Victoria Park. This extinct species is closely related to the New Zealand kōwhai and the fabled ‘Victoria Park toromiro’ was touted as an ex-situ conservation programme of threatened species.”

Sadly for the story, the research showed the Victoria Park tree was not a survivor of an extinct species, but was in fact Sophora godleyi, a species named earlier by Peter after late Manaaki Whenua botanist Dr Eric Godley.

The fourth study of an extinct plant, Trilepidea adamsii successfully showed relationships among three genera of New Zealand’s endangered mistletoes, Trilepidea, Alepis and Peraxilla.

“Using ancient DNA process and methods lets us explore both the stories around extinct species, and the actual relationships. The samples may be old, but they can be brought into contemporary science using modern techniques and approaches,” says Peter. “We’ve been able to resolve the status of some unique and poorly studied members of New Zealand flora.”

Peter emphasises, however, that this work underscores the importance of the collections in herbaria around the world. “The collections provide a baseline for what we have and what has been lost. While it is impossible to say whether L. depressa was always rare, or whether the type locality represented the last refuge of a once more widespread species, either way, it is clear the species would have vanished without record had Colenso not collected the single specimen.”

New Zealand has lost about 70 per cent of its forest ecosystems since the first arrival of people on its shores. Six plant species have gone extinct, with another further 350 species on the nationally threatened list. “In future, genomic analysis of ancient environmental DNA from sediments and fossil plant remains could provide a tool for exploring potential post-settlement species losses in the New Zealand flora,” says Peter.