Here's why:
* "Damo" means "grass" or "herb" in Tagalog.
* "San Juan" is the Tagalog translation for "St. John".
Therefore, "Damo ni San Juan" directly translates to "St. John's Herb".
However, it's worth noting that "Hypericum perforatum" is also used in Tagalog, as it's the scientific name of the plant.