Subspecific lion taxa has long been subject of debate and discord among feline taxonomists. For the longest time, sixteen to eighteen different variants have been acknowledged as valid subspecies of lions, but most of these assertions were based on morphological characteristics judged by European biologists centuries ago, before advancements in genetics allowed individuals to give more legitimate unbiased interpretation of subspecific taxa. For simplicity, the IUCN currently only recognizes Panthera leo leo as the trinomial name for all African lions and Panthera leo persica for all Asian lions.
In 2014, Ross Barnett et al. published his study analyzing the mtDNA of lions to determine evolutionary and geographical history between populations. Barnett et al. determined that the mitochondrial differences between lions of India, northern Africa, western Africa, and central Africa are untenable. Likewise, differences between lions of southern and eastern Africa are also untenable. The populations between the Asian-equatorial northern African and equatorial southern African have been separated for approximately 100,000 years ago due to blockage by geographic formations such as the African Rift Valley, preventing gene flow between the populations. Based on these findings, Barnett et al. suggest that only two lion subspecies should be identified: Panthera leo leo (for lions north of equatorial Africa, western Africa and Asia) and Panthera leo melanochaita (for lions of south of equatorial Africa and east Africa). (https://bmcevolbiol.biomedcentral.com/articles/10.1186/1471-2148-14-70)
Barnett et al.'s study was acknowledged by the IUCN in their 2016 revision of Panthera leo. However, they cautioned that further genetic research was needed to better understand the relatedness between lion subpopulations, as mitochondrial DNA is only inherited from mothers. The IUCN was hesitant to officially adopt any taxonomic revision without exploring the entire genome, which is currently in preparation by Laura Bertola et al. (http://www.iucnredlist.org/details/15951/0)
A verdict was reached and published in 2017 that further supports the findings of Barnett et al. The IUCN Cat Classification Task Force fully accepted and supported the revised subspecific taxonomy for lions: there are now only two. (http://www.catsg.org/fileadmin/filesharing/5.Cat_News/5.3._Special_Issues/5.3.10._SI_11/CN_Special_Issue_11_Revised_taxonomy_of_the_Felidae.pdf) It is likely the IUCN will adopt this new taxonomic setup when they next revise their Panthera leo page. If not, it might be left alone solely to help preserve lion populations in Asia (which - under Panthera leo persica - are considered endangered). A similar take is done for African forest and African bush elephants - they are regarded as one species by the IUCN solely for the protection of hybrids. (http://www.iucnredlist.org/details/12392/0)
With this new concrete information, I propose the following for iNaturalist:

Panthera leo leo should be reactivated, as it no longer solely represents the extinct Atlas population of lions.
Panthera leo azandica (Congo lion), Panthera leo persica (Asiatic lion), Panthera leo senegalensis (West African lion), and Panthera leo kamptzi (Cameroon lion) should be subsumed into Panthera leo leo.
Panthera leo melanochaita should be added as a taxon (or reactivated if already in the iNaturalist database as the extinct Panthera leo melanochaitus).
Panthera leo bleyenberghi (Katanga lion), Panthera leo krugeri (Transvaal lion), and Panthera leo nubica (Maasai lion) should be subsumed into Panthera leo melanochaitus.
The extinct Panthera leo spelaea (Eurasian cave lion) and Panthera leo atrox (American cave lion) should be treated as individual, unique species separate from Panthera leo (as Panthera spelaea and Panthera atrox, respectively). This assertion is based on the fact that the cave lion and lion branched from a common ancestor 1.9 million years ago (Barnett et al. 2016
https://www.openquaternary.com/articles/10.5334/oq.24/) and potentially coexisted on the Iberian Peninsula independently without having hybridized (Sommer and Benecke 2006 http://onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.2005.00040.x/abstract;jsessionid=64DB41D50DB678F4E3479997D8313B01.f03t01?systemMessage=Wiley+Online+Library+will+be+unavailable+on+Saturday+25th+March+from+07%3A00+GMT+%2F+03%3A00+EDT+%2F+15%3A00+SGT+for+4+hours+for+essential+maintenance.++Apologies+for+the+inconvenience). Panthera atrox, relatably, is thought to have branched from Panthera spelaea approximately 200,000 years ago.

I'll retain Panthera leo persica until either 1) iNat decides to adopt a more flexible taxonomy or 2) IUCN officially subsumes this taxon under P. l. leo as recommended by the cat specialist group.

And for clarification: Panthera leo azandica (loc. typ. Vankerckhovenville, NE DR Congo) should be a synonym of the Northern rather than the Southern lion.

Hi @bobby23, as mentioned above, iNat's mammal taxonomy currently follows IUCN's Red List (as published at www.iucnredlist.org), but this might change. Synonymizing (rather than splitting) a taxon in iNat is easily done, and I'd prefer to see what the new policy turns out to be before we make too many changes.

Feel free to flag taxa, that's always a good starting point for subsequent changes.

Cheers, Jakob

can we resolve this flag? Or is there still ssp curation that needs to be done?