A rare and threatened plant species has been found near Melrose in the lower Flinders Ranges.

Ecologist Jean Turner said the spiny daisy was now known to be at just six sites, all in South Australia.

She said all the plants at each particular site were genetically identical, but there were genetic differences between sites.

Ms Turner said threats to the species included weeds and spraying.

"The spiny daisy is quite unusual in that it basically grows by suckering so it does produce flowers and it does produce pollen but it doesn't seem to produce any viable seed and the populations that we've discovered are all quite isolated from each other," she said.

"All of the populations that we've found are on roadsides or railway corridors so they're very vulnerable to weed invasions, accidental damage, for example, with road maintenance work. It's also threatened by browsing, for example, the European white snail and also rabbits can have an impact on these plants."