Rubus bifrons? R. armeniacus? Which one? Are they the same species?
I won't get to the bottom of this issue in a single journal entry. But I thought it would be prudent to outline a bit of the issue.
There is clearly a debate going on over whether to combine R. bifrons and R. armeniacus or not. iNaturalist adds to the confusion somewhat by keeping them separate instead of making a determination. 'Flora of North America' lists them as synonyms and defaults to the older name (http://floranorthamerica.org/Rubus_bifrons). Many of the flags on the iNat taxon pages refer to this.
However, you will invariably see curators point out that iNat does not use FNA as its plant authority. This website uses 'Plants of the World Online': https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:735202-1
So there is a difference of opinion at a high level.
It is interesting to read the opinions of scientists based in Europe. The debate over the two species seems to be exclusively a North American problem. In Europe the two species are clearly separate. User enkidoo has written an opinion on this with details on how to separate the two species:
I can only answer from a Central European viewpoint (leaving aside the fact that the name Rubus armeniacus has been misapplied to a species not meant by the original author):
In Germany and neighbouring countries R. armeniacus and R. bifrons are unanimously separated and with (imho) good reasons. Though they have some features in common (apart from the fact that they both belong to Series Discolores), like e.g. the straight prickles in the inflorescence and the +- hairy stem (but the manner of hairiness clearly differs) other features are clearly different, e.g. lower lateral leaflets digitate (armeniacus) vs. pedate (bifrons), leaves +- convex (at least most of them most of the time, armeniacus), leaves always flat (bifrons), upper surface matt (armeniacus) +- shiny (bifrons), petal and fruit size also differ (both larger in armeniacus). R. armeniacus (the species currently labelled so) is an introduced species of obscure origins (I haven´t seen any clear evidence that it really stems from the Caucasus, but I also can´t rule out that possibility), whereas R. bifrons is a native of southern temperate and northern mediterranean countries
I am inclined to keep the species separate, and I believe most of the species in North America are in fact R. armeniacus with some limited range of R. bifrons (here is one reference: https://www.cal-ipc.org/wp-content/uploads/2017/10/Dispatch_2017SummerFall.pdf and another which supports them as separate species, with R. armeniacus [or possibly a hybrid with other Rubus spp.] being the dominant one in western NA: https://www.fs.usda.gov/database/feis/plants/shrub/rubspp/all.html).
It might be interesting to do a genetic study of the two species and compare them to European populations, to see if the NA populations have truly 'despeciated' as some have suggested. However, I am not a plant taxonomist. I have only gotten interested in this topic because the pest Agrilus cuprescens, the rose stem girdler, uses Rubus as a host. I did a survey a couple years ago and found them in Armenian/Himalayan blackberry and I still haven't been able to figure out exactly which species it was.
I think this debate highlights how important it is to remember that iNaturalist is an international resource. This site is not exclusive to North America. If these species were native here, an argument could be made to supersede POWO with FNA, but that isn't the case.
See these flags for some more background:
https://www.inaturalist.org/flags/496149
https://www.inaturalist.org/flags/537809
https://www.inaturalist.org/flags/385864
