The first part is the name of the botanical genus and always is written with an initial capital letter. The second part is a word which identifies a particular species in that genus, and it is never capitalized today. Thus the binomial name Tanacetum parthenium , or feverfew in English, refers to one species in the genus Tanacetum. Tanacetum vulgare is another species, or European tansy, now a common roadside weed in America and elsewhere. The binomial name sometimes is abbreviated, such as T.parthenium , if the generic name has been written previously and is clearly evident.
Research continues on the plants and their evolutionary relationships.
Because of this, unfortunately, there are some Latin name synonyms to deal with, but under the procedures of the International Code, this difficulty can be overcome in systematic fashion. As throughout modern science, the system over time is constantly improving and is self-correcting. Errors get weeded out and corrected. Technically, the full botanical name for an herb species includes the name of the author or botanist who first described the species and subsequent authors who may have created a new name for that species, in a different genus. Today, the best and most authoritative herb books and references include this full botanical Latin name plus author citation for any herbs being discussed in depth.