Vietnamese Coriander and "Saw Mint"

The plant you sell as "Vietnamese coriander" is not the same as what is considered "Vietnamese Coriander" in southeast Asia. There is a plant that is almost exactly like Mexican coriander except it doesn't grow the prickly seed things on top - not as interesting to look at but much more culinary usefulness. It is sold as "saw mint" in the western groceries in SE Asia, but tastes exactly like mexican coriander and is used interchangably with cilantro. The broadleaf herb in the picture is also used there but has a different and stronger flavor (if it is what I think it is, I really should buy some and try it before I get too outspoken) Anyway if you were to get the "saw mint" variety of vietnamese coriander, I, for one, would buy some.

In fact, our "mexican coriander" is from Vietnam. Interestingly, the species, Eryngium foetidum, is popular in both Mexican and Southeast Asian cuisines. In Mexico it is called "culantro" and in Vietnamese it is called "Ngo Gai". As far as we can tell there is no difference between the mexican and vietnamese forms, and we suspect that they are virtually one and the same.
You mention the "prickly thing on top". This is the flower. In Vietnam the plant is never allow to reach the flowering stage so that the fresh product always consist of leaves only. The photo in our catalogue shows the thorny head that the species develops, and this prickly head is the reason why the plant is also known as "thorny coriander".
We agree that the plant called "vietnamese coriander" in the West, Polygonum odoratum, is not used exactly like coriander in Asia. Its use as a coriander substitute is a western development in the search for a plant with a cilantro-like flavour that can be grown indoors more easily than true cilantro.