Sources:
https://www.merriam-webster.com/words-at-play/difference-between-herb-and-spice
https://www.etymonline.com/word/cassia
https://www.cinnamonzone.hk/cinnamon_history_a.html
https://www.spiceography.com/cassia-cinnamon/
https://www.spiceography.com/ceylon-cinnamon/
https://pfaf.org/user/Plant.aspx?LatinName=Cinnamomum+verum
http://plantsoftheworldonline.org/taxon/urn:lsid:ipni.org:names:682369-1
http://www.todayifoundout.com/index.php/2014/01/brief-history-pepper/
https://www.jstor.org/stable/20463498?seq=1
https://archive.org/stream/naturalhistoryof03plin/naturalhistoryof03plin_djvu.txt
https://www.almanac.com/where-does-black-pepper-come
https://extension.psu.edu/herb-and-spice-history
https://www.allrecipes.com/article/white-pepper-vs-black-pepper/
https://www.mccormickscienceinstitute.com/resources/culinary-spices/herbs-spices/cinnamon