Well, the ayes seem to have it. I guess John knows what he sent and cichlidsrgr8 evidently has corroborated. I've grown both and went though a very similar situation where I sent another member one specimen thinking it was the other. So this is why I have some doubts. It was only when I raised both simultaneously in an EI tank that I was able to tell the difference, so nutrient levels have an effect on appearance. I imagine there are also morphological differences depending on the supplier.
In a low-to-moderately dosed tank they look very similar but in a heavily dosed tank they are night and day. This difference is clear at the beginning where they are very different submersed form.
Here is P. Stelleta (Eustralis) only a week or two after submersion. The Tropica version of this plant has an emmersed form very similar to it's submersed state, with very spiky stelleto knife shaped leaves. The transition from one emmersed to the submersed is practiacally seamless.
On the other hand aromatica's emmersed form looks nothing like its submersed form. The only photo I have that shows the difference in the two forms is this one. You can see in the middle a couple of emmersed shoots surrounded by a forest of the submersed stems. There is a radical difference and it takes ages to go from one to the other. So the question might be: what did the plant look like at purchase? If it was already spiky it could be stelleta. But because of the difficulty in transition of this plant, vendors often sell aromatica in the submersed state, so the appearance at purchase is by no means definitive.
As both plants grow in an EI tank their differences become magnified. P. stelleta's stem becomes engorged and it throws out annoying white aerial roots. The leaves can grow to 3 inches which means a crown diameter of up to 6 inches or more. On the the surface of the leaves, Tropica's stelleta tends to be smooth with a pronounced pale vein running down bisecting the span of the older leaves. Younger leaves at the crown are more upright, only flattening out to the horizontal as they are eclipsed by newer growth above.
On the other hand, I've not seen aromatica leaves much longer than and inch or so meaning a crown diameter of a 2 to 3 inches. Again, that might be just due to my supplier and there may be aromatica versions which grow wider crowns. L. aromatica has a waffled leaf surface texture, and the leaves have a more horizontal posture at the crown during the earlier hours of the photoperiod. Both quickly close up to the vertical near the end of the photoperiod so the comparisons depend on what time of day they are observed.
Cheers,