Hoja santa (piper auritum) is a large herb leaf used in cooking in southern Mexico. The hoja santa leaf is typically used fresh for moles, wrappers for tamales, and even medicinally as an anti-inflammatory. The leaf imparts a slightly anise-like flavor. Typically only the fresh leaves (raw or toasted) are used in cooking but you can find the dried herb too. Dried hoja santa is usually used for making tea.
This herb should not be eaten in large quantities because it does contain some toxic properties, specifically, safrole and caphoradione A&B (alkaloids). Typically recipes use very small amounts of the herb as a flavoring. It is widely used in Mexico as well as in South American cuisines.
If you don't have hoja santa you can substitute:
Look for the large fresh green leaves in Mexican markets or farmer's markets. It grows wild in some parts of California so if you're in that state you may have better luck finding it. You can buy the dried leaves, live plants or seeds to grow your own on Amazon.com: Hoja Santa.