[Wikipedia] Native to the shores of the Mediterranean: Fennel (Foeniculum vulgare) is a flowering plant species in the carrot family.[1][2] It is a hardy, perennial herb[3] with yellow flowers and feathery leaves.[4] It is indigenous to the shores of the Mediterranean but has become widely naturalized in many parts of the world, especially on dry soils near the sea-coast and on riverbanks. (contributed by Mary Ann Machi)

[Cal-IPC] Impact on many plant communities: Foeniculum vulgare (fennel) is an erect perennial herb (family Apiaceae). Although the plant is very common throughout the state, dense local populations have been reported from Santa Cruz Island, in fields around the San Francisco Bay region, Palos Verdes Peninsula (Los Angeles County), and Camp Pendleton (San Diego County). It can drastically alter the composition and structure of many plant communities, including grasslands, coastal scrub, riparian, and wetland communities. It is still unclear whether culinary varieties of fennel are invasive. (contributed by Mary Ann Machi)