Culantro (Eryngium Foetidum) grows in southern Mexico in the coastal areas. It is referred to as "parsley" in the Tabasco region of Mexico. The leaf is quite tough so it is not typically eaten raw but added to soups and stews. The flavor of culantro is similar to cilantro. Overcooking will destroy most of the flavor so it should be added to the dish either midway or towards the end of the cooking time. One popular dish is Caldo de Pollo (chicken soup).
Other popular uses include salsas, sofrito and recaito which is a Puerto Rican sofrito.
This herb is also popular in many other countries including, Caribbean, Thailand, Malaysia and Puerto Rico, and Vietnam.
Look for this herb in Mexican markets with a well-stocked produce department, or find in Vietnamese markets (look for ngo gai) pronounced "no guy". The plant is moderately easy to grow once it gets established. You can purchase seeds online at Amazon.com: Culantro - Ngo gai Seeds. The plant is best grown in the shade in order to produce the dark green leaves. Another reliable source is Kitazawa Seeds.
If you don't have culantro you can substitute:
Culantro is high in vitamins A, B1, B2, and C. A 100 gram serving (about 6 3/4 cups) contains 23 calories, 0.6 grams of fat, 4 grams of carbs and 2 grams of protein.