An "unlikely pair" of Australian plants have been named after actors Danny DeVito and Arnold Schwarzenegger, stars of the cult '80s comedy Twins.

Australian National University researcher Professor Mike Crisp leads a team that had studied the "egg and bacon pea" flowers for decades.

However, biologists only recently discovered the plants were actually twin species.

"It was a really big surprise that what we previously thought was one subspecies of another species was actually two species … it's such an unlikely pair of twins, if you like," Professor Mike Crisp said.

In the film Twins, Schwarzenegger discovers he and DeVito are the result of a secret experiment to make the perfect child.

But the embryo splits — and the twins become almost polar opposites.

Likewise, the Daviesia schwarzenegger is bigger and more robust, while the Daviesia devito is smaller and weaker.

Both species are at risk of extinction as they are native to bushland that is being cleared for wheat farming.

The Daviesia schwarzenegger is a robust plant, while the Daviesia devito is smaller and weaker. ( Supplied: Australian National University )

DNA testing improves research

Professor Crisp said it was not until DNA testing was done on the flower that the discovery was made.

"Traditionally — when I was a young taxonomist — we classified plants based on their external, physical appearance … that's all we really had to go with," he said.

"Then the revolution in DNA technology came along. Suddenly there was much more data available to work out exactly their genetic and evolutionary relationships."

Professor Crisp said the technology has had similar implications for the work of thousands of biologists.

For example, a team doing similar DNA analysis on lizards in northern Australia are finding "huge numbers" of previously undiscovered species, by comparing the genetic material of lizards once thought to be from the same species, Professor Crisp said.

The species are genetically isolated from each other.

"And that means all the other features of the organisms … they're all likely to differ too," he said.

"The results that scientists got before they knew there were multiple species might be invalid, because they've been compounding important differences that might not have been obvious."

DeVito and Schwarzenegger were approached for comment.