Australian Customs has destroyed two irreplaceable plant specimens loaned to scientists by New Zealand and French institutions.
New Zealand's Allan Herbarium and France's National Museum of Natural History sent the samples of lichen specimens, which dated back to the 19th century, to Australia for research - but they were intercepted by Customs and incinerated.
Neither the French or New Zealand institutions, nor the Australian scientists, were told of the decision; normally both parties would be informed if there was a threat to destroy imports.
A spokesman for the Department of Agriculture says the packages did not give any indication of the intrinsic value of the samples.
Michelle Waycott, professor of plant systematics at the University of Adelaide, told Reuters the plants were being used to determine whether a new plant species had been discovered in Australia.
"These specimens are also the last remaining evidence that they were present in a particular location."
The Allan Herbarium has suspended all transfers to Australian scientists, until it can be sure they can be safely received.
The Border Security agriculture department has started to review its procedures.
Australia's border security laws are among the strictest in the world.