Answer: It is my understanding that recao refers to a blend of herbs cooked in butter or oil and then added to a stew or soup or braised dish for flavoring. Since sorrel adds a lemony flavor I suppose it could be added to the recao depending on personal taste.
I did find a different reference to recao as follows, but it does not include sorrel in this context:
"Recao Del Monte known as Eryngium foetidum known as (ngo gai)"
The Latin name for sorrel, the perennial salad and seasoning green used in Europe, is Rumex acetosa. I hope this helps answer your question.
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