Rosmarinic acid (RA; C18H16O8;Figure 32.1) is a polyphenolic carboxylic acid found in hornworts, in the fern family Blechnaceae, and in species of several orders of mono-and dicotyledonous angiosperms (Petersen et al., 2009). The mint herbs (family Lamiaceae) appear to be the most commonly used and studied sources. These include rosemary (Rosmarinus of”cinalis), basil (Ocimum basilicum), sage (Salvia of”cinalis), thyme (Thymus vulgaris), Perilla frutescens (a populargarnish in Japan), and mint (Mentha X piperita, Mentha spicata, and Mentha aquatica).