This study found that, of species tested, apparently spearmint (M. spicata) contained the highest levels of RA.
Sorry if this has been covered already. I have not read the entire thread.
Comparative study of rosmarinic acid content in some plants of Labiatae family
"The results showed that among analyzed plants belong to different genus of Labiatae family, the most RA contents were found in Mentha species. As it is observed in Table 2, all Mentha species contain RA in considerable concentration (19.3--58.5 mg g-1) and M. spicata showed the highest amount of RA. "
https://www.ncbi.nlm...les/PMC3307200/
