In january of 2015 this photo was published on Facebook a plant obtained as "blassii". The appearance of this particular specimen is so radically different from what we think of as blassii that some doubt of this ID arose, not unreasonable considering how different the appearance of this plant is, but one additional piece of information made this much more believable - the plant was grown under "high light" aquarium conditions with optimal fertilization, CO2 and extremely strong light.

I tihnk it's blassii for these reasons:

1. So many plants are called blassii that this name represents the full range of diversity in of leaf shape in the C. cordata complex.

2. I had experience once with C. undulatus which I had grown for years and knew as a tall green plant but we I switched to closer to optimal conditions and much stronger light the leaves changed to shorter brown tiger-striped leaves so different from the green leaved from you'd swear it was a different species.

   The size of the plant rules out, in my opinion, it being anyhting but a cordata morpho-species.

3. I think it is C. cordata Cara and can't be C. undulatus if for no other reason than the size - UND never gets that big. It also doesn't look like C. undulatus when grown under high light, which the bullate leaves tell me is what it was grown under - that doesn't happen in dim to average light.

4. The physical appearance of the leave more resembles cordata siamensis more than any other plant in the genus.

But you're right it doesn't look like COR, named because of it's cordate leaves. But keep in mind cordata really properly describes a species complex and not just a single species.

As we learn more about the genetics of these things what we find is, instead of a nice genetically distinct 15 different species in the area or something there's cordata and a small number of other species and about as many natural hybrids.

Look at this for example this is just the C. cordata forms on the Island of Borneo:

There's a breakdown of the genetics here:

http://crypts.aquaria.net/species/alpha/s/SIA/

But in a nutshell it's:

C. cordata var. cordata is the 2n=34 karyotype and found in Southern Thailand, Peninsular Malaysia and one known location in Sumatra. Mostly acid-loving blackwater plants. C. cordata var. siamensis is the form from Thailand with a chromosome compliment of 2n=68,85,102 and forms exist that live in acidic black water while other forms exist from limestone biotopes and do well in hard water. C. cordata var. grabowski is the n=68 other form from Borneo, nearly all of which are from black water peat swamps. "C. cordata var. diderici differs from the other varieties of C. cordata by having a more rough limb of the spathe that varies in colour from brownish to almost reddish. The inside wall of the kettle is white to purple (may have some fine red dots) and the top of the spadix is purple. As you can see from the chromosome number it appears to be the same as that found in var. siamensis. Further investigations are needed to illuminate their relationships." Per: Jacobsen & Bastimeijer - "On Cryptocoryne cordata var. siamensis." T.A.G. (in V27#2 Apr-Jun 2014)

Ever since cheap cam cell phones, pictures have been coming in from Asia and the DSLR changed that so much it's ridiculous and what's obvious now is not as many of these lived in peat swamps as you'd think, a lot grow in rivers with rocky substrates reminiscent of course aquarium gravel mixed with sand, no the small stagnant tea covered bog they refer to here, the true peat bog plants.

This plant is C. cordata siamensis, one of the hard water Thai species known for it's lanceolate leaves and commonly sold under the trade name "blassii". Here's the closest photo I could find to this plant. Notice the high light and that the leaves tend towards the horizontal.

So uh, yeah that part is embarrassing. We have no idea what's going on really and they're studying exactly this now in labs in Europe looking at the DNA, but there are SO MANY - hundreds - of plants with the C. cordata tag. It's going to take a while.

But, that DNA breakdown does at least provide some sense in all of this - previously we'd just assign species name by guessing at the leaf shape ands that didn't work out so well - here's a half dozen relic species that all turned out to just be C. cordata.

There's more infornaton about cordata relics here

In low to average light cordata will point its leaves straight up. If the light is intense enough it will lie its leaves down flat and with enough light they'll become bullate, too.

I never grew blassii long enough to notice it under high light and optimal fertilization, but I did with undulata and it exhibits the same effects becomes more lanceolate, bullate and even more colorful with a rather striking pattern when grown under very good conditions, while is just a green plant when grown under average to less than average conditions (and that's with what we might think would be good light and nutrition, in this case fluorescent "grow" tubes and a manure and minerals base layer capped with 6" of sand.

But no. However with four tubes and high levels of water column fertilization and CO2 the plant changes dramatically as these photos show:

Before:

After: