erba di San Pietro

Two entirely different herbs.

In Liguria, it's crithmum maritimum, or rock samphire, better known as finocchio marino or sea fennel. A good garnish for seafood. Along the Riviera del Conero in Le Marche it's called paccasassi, and often served on pasta mixed with ricotta; in the Slow Food Presidium.

Also known as frangisassi.

Elsewhere, it's a minty, slightly bitter herb, tanacetum balsamita, also known as balsamita or menta romana. In English, costmary or balsam herb.