It may be too late to save many species of plants from extinction at the hands (or vines) of invasive plant species.

Researchers from South Africa and Australia teamed up to study how invasive plants were linked to the extinction of native species. In order to have a framework to study and discuss their observations, they developed an "extinction trajectory" that consists of six steps plant species go through during the extinction process.

Though there have been no proven plant extinctions as a result of invasive species to date, the authors of the study believe that many may already be functionally extinct. In other words, the plants do not have the means to sustain their population.

"The main reason why there is no clear evidence of extinction that can be exclusively attributed to plant invasions is that invasions have not been around long enough," co-author and professor at Stellenbosch University's Centre for Invasion Biology Dave Richardson said in a release.

"Our research shows that plant extinction is an agonizingly slow process. However, red flags are evident in numerous locations around the world-species that now exist in fragmented populations, with radically reduced opportunities to reproduce."

The six "thresholds" in the extinction trajectory are as follows:

1. Plants die quicker than they can be replaced by their offspring in some locations.

2. Plants disappear from some locations entirely, but potential offspring remain as'propagules', seeds or spores that could regenerate a new cohort of individuals.

3. Some locations lose both individual plants and their propagules. With no plants or seeds, this is a local extinction.

4. The last locations hosting a species lose their individual plants, but in some places seeds or spores remain in the soil.

5. The species is entirely lost in the wild with no individuals or propagules. The only survivors are held in botanic collections.

6. Extinction. The remaining plants are lost, and the remaining seeds or spores are no longer capable of becoming new plants.

Richardson and co-author Paul Downey from the University of Canberra published their paper in journal AoB Plants earlier this month. The impending extinction of native plant species will be hugely disruptive to local ecosystems and begs immediate attention.