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Marsh Barbel is a stout aquatic perennial herb

Marsh Barbel  flower

Marsh Barbel  (Hygrophila schulli)  Habitat photo from Sadivayal, Siruvani, Coimbatore.  Kokilaksha, as it is known in sanskrit, was extensively used in Ayurvedic system of medicine for various ailments like rheumatism, inflammation, jaundice, hepatic obstruction, pain, etc. Ref:
http://www.flowersofindia.in/catalog/slides/Marsh%20Barbel.html