The IMO most advanced literature on systematics and ID of natural
(!) Echinodorus populations is this paper: Lehtonen (2008 ): An integrative approach to species delimitation in Echinodorus
(Alismataceae) and the description of two new species. http://www.sci.utu.fi/sivustot/amazo...2008_KBull.pdf
This treatment has only few pictures of the plants. A lot of detailed and exact drawings is in the Echinodorus monography from Haynes & Holm-Nielsen (1994) (http://www.nhbs.com/flora_neotropica...fno_41981.html
), although not up-to-date regarding taxonomy.
I personally think that to ID a crypts is easy as long as you can make it flowers, |
but echi is completely different.
Yes, it's often difficult as the characteristics aren't as visible at a glance as in crypts. It's rather the combination of several characters (e.g. number of stamens per flower + fruit stalk recurved or not + form of pellucid markings in the leaves + petiole cross section form + leaf form + ...) that's important for Echinodorus species recognition.
But ID of cultivated
Echis poses much problems, as many are actually hybrids, even if labeled as species. Apparently often unintentional or unnoticed crossings happened in culture. Also in the nature Echinodorus hybrids are frequent, as S. Lehtonen wrote. So Echi ID is often approximate.
Your plant has large roundish heart-shaped leaves and large flowers with many (much more than 12) stamens. I think it's something near Echinodorus floribundus
(= E. grandiflorus ssp. aureus = "E. grandiflorus" in older aquarium literature), although some other features have to be checked, as form of pellucid markings (laticifers) in pressed leaves (points in E. floribundus, lines e.g. in E. cordifolius). Plants like this are often also labeled as "E. cordifolius" in nurseries but don't belong to this species.
Your plant may be no pure E. floribundus as the inflorescences lay down, a feature that can be seen e.g. in E. cordifolius. Typical E. floribundus has rather upright inflorescences.