Culantro is a much deeper-flavored cousin of cilantro. The leaves are long and saw-shaped. I have replaced culantro with cilantro before. But remember that cilantro has a much sweeter taste than culantro. So, it is not an exact replacement, more like a 1 part culantro for two parts cilantro. Culantro can be found at Latin markets or under specialty items in the produce department of major supermarkets.