Lauren Fuge
For 170 years, botanists have believed that the rare daisy fleabane (Erigeron conyzoides) is an Australian native flower.
First described in 1855, the species is restricted to the alpine areas of NSW and Victoria. But it hasn’t been collected in NSW since 1978, and was recently listed as endangered in Victoria after not being sighted for 13 years.
When botanists rediscovered the species last year, genetic testing revealed a surprising taxonomic twist – that this presumed native is actually an introduced weed.
How does an imposter like this go unnoticed for so long? Let’s delve into the story of this wily weed.
Daisy detectives
Daisy fleabane was first described in 1855 by Ferdinand von Mueller, the German-Australian chemist and botanical collector. Mueller worked as the Victorian Government Botanist from 1853, was director of the Royal Botanic Gardens in Melbourne and also founded the National Herbarium of Australia.
Very little work has been done on the species since, though botanists knew it was different from other native daisies in the daisy family Asteraceae. It’s more similar to the invasive weed flaxleaf fleabane (Erigeron bonariensis), and so the two were assumed to be close relatives.
Cue the daisy detectives: CSIRO botanists Alexander Schmidt-Lebuhn and Stephanie Chen, from the Australian National Herbarium, set about to find daisy fleabane in the wild and learn more about it.
They wanted to figure out the relationships between daisy fleabane and other Erigeron species, to see if biological control agents that are used to target the invasive E. bonariensis were harming daisy fleabane too. Australia has more than 3200 introduced plant species, which can pose problems for native ecosystems and agricultural land alike.
So Schmidt-Lebuhn and Chen went searching in the Australian Alps in January 2024. They targeted three sites where daisy fleabane had been seen before – and they found it.
It was growing along a dam wall in amongst other weed species, near Falls Creek in Victoria.
Upon rediscovery, the researchers realised that daisy fleabane (E. conyzoides) looks very similar to another flowering plant from the same family, bitter fleabane (Erigeron acris), native to the northern hemisphere. The scientists noted that the 2 species share strong similarities in growth form, habit, flower structure, and leaf arrangement, shape and size.
“If specimens of our E. conyzoides were presented to a northern hemisphere botanist without location data, its purple stems and plant structure would likely lead them to confidently identify it as E. acris, especially if accompanied by a description of its alpine habitat,” Schmidt-Lebuhn says.
The team also didn’t find any daisy fleabane growing in the surrounding bushland. This is noteworthy because weedy daisies often prefer to grow in disturbed areas, like roadsides.
Suspicions were growing that daisy fleabane wasn’t what it seemed – but the real test came next.
Oops-a-daisy
The team brought the new samples of daisy fleabane back to the lab and performed genetic analysis on the leaf tissue.
“We’re now using a sequencing technique called target capture to look for specific genetic markers called angiosperm 353,” Chen says.
These markers are genetic signatures which occur in all flowering plants.
“It’s designed so that it’s universal across flowering plants, so whatever you throw at it, it will capture it,” Chen says.
And the results confirmed the suspicions: E. conyzoides and E. acris are one and the same. Daisy fleabane – presumed to be a rare native flower – is, in fact, an introduced weed.
But when two species become one, which one keeps its name?
The rule is simple: the first species to be named remains the same, and the other must be synonymised, or ‘un-named’.
This means daisy fleabane is no more; the species is now known as bitter fleabane (E. acris).
A tangled history
But how was E. acris mistaken for two species for so long?
Let’s go back to 1855, to the botanist Mueller.
He collected what he thought were daisy fleabane specimens from two locations around the sources of the Murray River and the Snowy River, where it’s possible that graziers accidentally introduced the species on contaminated equipment or produce. From the early 1820s, graziers introduced livestock to mountainous areas, pushing up into the alpine when there were droughts.
The geographical origins of E. acris are still unclear, according to the researchers.
“The specimens looking closest to what we have here are from near Alaska and Siberia,” says Schmidt-Lebuhn. “On the other hand, there may be other forms looking just like it in Scandinavia that simply haven’t seen.”
It’s possible that the seeds could have arrived with settlers from these subartic northern regions, and spread by graziers.
Perhaps since many of the early weeds introduced to Australia came from Britain or Ireland, Mueller may not have recognised daisy fleabane as an invasive species when he first collected it.
Another piece of the puzzle is the places where E. acris likes to grow. The fact that this weed wasn’t spotted in the field for so long seems to indicate that it relies on human-disturbed environments with low competition from native species.
“The species has not been collected in New South Wales since 1978, but has persisted in Victoria,” Chen and Schmidt-Lebuhn write in their paper, the Australian Journal of Botany published by CSIRO Publishing.
“This parallels the removal of livestock from the Alps in both states, which happened much earlier in New South Wales. Grazing was removed from the alpine areas of Kosciuszko National Park in 1958, but only much later from many parts of the Victorian Alps, such as from the Howitt Plains in 1988 and from the Bogong High Plains in 1991.”
This removal allowed native vegetation to recover, which would have provided competition for the weed and likely led to its decline.
“This behaviour is consistent with the hypothesis that it is a European introduction,” the researchers write.
The species is now available to the wider research community, with seeds stored at the Victorian Conservation Seedbank and the National Seed Bank.