Echinodorus tennelus is not a crypt ainsy. States in the name it is in fact a specie Echinodorus lol.
Growth doesnt appear to be either E. tenellus or C. parva IMO. Cryptocoryne Willisii does spring to mind. Its seems a little too paddle shaped to be parva IME, mine has always had the paddle shape on the end of the leaves but never that big, it also doesn't appear to be growing as compact as Parva does in any tank i've seen it in. Conditions will vary and effect this though. When i tried E. tenellus it also did not grow anyway like this. The image provided for tenellus i believe to be emerged growth, submerged growth tends to be more grass-like, with the plant losing its paddle shaped tip almost entirely. As the OP stated, they have had this plant for over a year now, so i think that points away from tenellus for the most part. Don't qoute me on that though, its only my understanding from previous reading of the plant. I do however believe it to be a Cryptocoryne of sorts, just unsure as to which exactly.
James