Wikipedia
Platostoma
Platostoma is a genus of flowering plants in the mint family, Lamiaceae, first described as a genus in 1818. It is native to tropical parts of Africa, southern Asia, Papuasia, and Australia. Mesona and Acrocephalus has been known as its synonyms.
A widely consumed species in this genus is Platostoma palustre (synonyms Mesona chinensis, M. elegans, and M. procumbens), or xiancao in Mandarin, sian-chháu in Taiwanese, leung fun cho in Cantonese, sương sáo in Vietnamese, and cincau in Indonesian and Malay. It is eaten as a snack in drinks, or set as a gel and served as a grass jelly.
In Indonesia the Platostoma palustre leaf is used to make a black jelly; there is also an instant powder variety available.