I've read several threads about Petco selling plants that are not true aquatics. How do you tell the difference?
As a
general rule for stem plants, if the LFS employee pulls them from the tank and they remain erect, it is probably not a good idea to buy it. The plant is either not a true aquatic plant or it is something that has been grown emmersed. Emmersed plants will usually convert back to a submersed state but you can expect to see a lot of the stems die and not make the conversion. While the price may seem good at the time, it will probably be cheaper to buy a submersed plant from a hobbyist, even after the cost of shipping.
The same is
generally true for rosette/rhizome plants with the exception of Anubias species. It is a little harder to tell on these types of plants but with submersed growth sword plants the majority of leaves will drop to more of a horizontal position when they are pulled from the tank. The same thing with emmersed grown Hairgrass...the leaves will tend to drop to a horizontal position out of the water. If the leaves remain erect, it is either not a true aquatic or it has been grown emmersed.
As with all rules, there are exceptions such as Anubias species mentioned above but most of the other "exceptions" I have not seen for sale in a LFS.