For Hygrophila
Daniel, T.F. 2013. Taxonomic, distributional, and nomenclatural notes on North American Acanthaceae. Mem. N.Y. Bot. Garden 108: 85-114.
Les, D.H., and R.P. Wunderlin. 1981. Hygrophila polysperma (Acanthaceae) in Florida. Florida Sci. 44: 189-192.
Long, R.W. 1970. The genera of Acanthaceae in the southeastern United States. J. Arnold Arb. 51: 257-309.
Wasshausen, D.C. 1998. Acanthaceae of the southeastern United States. Castanea 63: 99-116.