This species was formerly classified (and still is by some authorities) as a variety of P. amphibia, P. amphibia var. emersa.  P. coccinea is mostly terrestial unlike P. amphibia ( or P. amphibia var. stipulacea ) that is fully aquatic.  P. amphibia has branches and leaves laying on the water &  short primary inflorescence while P. coccinea has upright leaves & long (up to 90mm) primary inflorescence.