Genus, species, authority
Matricaria chamomilla L. — the genus, the species, and the person who first published the name, abbreviated. The authority matters more than it looks: it is how two different plants that were given the same binomial by different botanists are told apart.
The multiplication sign
Mentha × piperita is a hybrid, not a species, and the sign is not a letter x. Peppermint is a sterile cross of watermint and spearmint, which is why it cannot be grown from seed and why every plant descends by cutting from a small number of clones.
Synonyms, and why a name changes
Tulsi is Ocimum tenuiflorum, and Ocimum sanctum — the name most Indian sources use — is a synonym for the same plant. Cassia’s accepted name is Cinnamomum aromaticum, and the Cinnamomum cassia the whole trade uses is recorded by the USDA as an invalid designation. Neither is a mistake by the people using the older name; taxonomy moves and commerce does not.
What to do with it in a shop
Look for it. A seller who prints Aloysia citrodora is telling you which verbena you are buying; a seller who prints 'verbena' is not. Where TeaHQ records a binomial it is because the name is settled, where it omits one it is because the name is contested, and twenty of them were checked against a taxonomic authority in Sprint 18.