The species belonging to the so-called "Morelloid Clade" have never been so easy to identify. Here they are two revisions that can be helpful for this purpose:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6070582/pdf/phytokeys-106-001.pdf

https://www.bioversityinternational.org/fileadmin/migrated/uploads/tx_news/Black_nightshades_Solanum_nigrum_L._and_related_species_337.pdf