Hi I may be wrong, but they could be flowerbuds of Hibiscus sadariffa which is just one of several edible hibiscus species. It is related to Okra and along with several other Mallows. You might just see it a www.seedstosupper.com
George

Could it be Sesbania grandiflora? According to the link below, it is known as su dua in Vietnam.

Here is a link that might be useful: Sesbania grandiflora

Thanks for your help!

Yes, indeed it's Sesbania grandiflora. Vietnamese people use the flower or better the flower buds to cook the soup with fish or shrimp. Besides, they can just stir it with beef. The right name is "so dua".

So it should read as "bong so dua". "bong" = flower in Vietnamese. "so dua" = name of the plant. And the reason they call "so dua" because after flowering the bean pots look like the chopsticks. "dua" = chopsticks. "so" means not even. "so dua" mean not even chopsticks.

Hope this helps.
Alpharetta

Some Asian vegetable are unpalatable to westerners and people from other parts of the world. Take BITTER MELON for example; It will be stil bitter after soaking and changing water for days. I even burry sliced BM in salt, that extract the bitter juice out, stil it will be bitter.

I try most of asian veggies and fruits and stick to the ones that are agreeable to my taste. So don't expect every Asian veggies to be wonderfull.