Cuu ky is an herb that my ba noi (Vietnamese paternal grandmother) would often cook during the summers because it was "cooling." I've posted before about the concept of hot and cold, or yin and yang foods in Chinese food therapy. Without a common English name, or scientific classification though, I can't offer up much info. I just know it's supposed to be good for me. I've never eaten it raw, only in a light broth-based soup.
The plant looks like the picture below. The stems can get wooden if it's too old. There's also a few thorns, so be careful. Pluck the leaves only to make the soup. My second-youngest aunt was in town recently during a heat wave and made a "cooling" healthy soup with cuu ky and Rau Ma (Vietnamese Pennywort).