Five years after starting this topic, I finally found something this morning that I've been looking for here all that time and longer. Eryngium foetidum.
Variously known as sawtooth coriander, culantro (not cilantro), Mexican coriander, Thai coriander, long leaf coriander and many other names. I first encountered it as ngò gai in Vietnam. With a similar but stronger taste than the well-known cilantro or coriander leaf, it also retains its flavour when dried, unlike its more famous near-namesake.
Here it is known as 广东香菜 (guǎng dōng xiāng cài) or Guangdong coriander, although it has no real connection with that province.
