Hello,
I’m portuguese, we’re mostly familiar with lemongrass Cymbopogon citratus used in tea. I recently tried Tom Yum which started a discussion about what type of lemongrass is used with the dish. Wikipedia says most common and used for cooking is Cymbopogon citratus. But on the videos i see them use stalks which seems to be part of Cymbopogon nardus, known as citronella grass, since Cymbopogon citratus doesn’t have stalk or has very thin ones.
