More powerful AI says:

No, not all lettuces are the same species, although many commonly consumed lettuces (e.g., iceberg, romaine, butterhead, oakleaf, and leaf lettuce) belong to the same species, Lactuca sativa.

However, some plants commonly called "lettuce" belong to different species or even genera. Examples include:

Lactuca sativa: The typical garden lettuce varieties (iceberg, romaine, butterhead, oakleaf, loose-leaf lettuces).

Lactuca serriola: Wild lettuce, an ancestor to cultivated lettuce.

Valerianella locusta: Corn salad or lamb's lettuce, commonly consumed as lettuce but from a different genus.

Cichorium endivia: Endive, sometimes called lettuce but technically not in the lettuce genus (Lactuca).

Eruca vesicaria (Arugula or rocket): Often mixed with lettuces but belongs to an entirely different genus and family.

In summary, while most common lettuces belong to a single species (Lactuca sativa), not everything commonly called lettuce or used similarly in salads is botanically the same species or even genus.