i don't know much about the plant, but when you get a plant, trust your fish's judgement. If they won't go near it, or are acting weird when you put it in, I say take it out. And, more importantly, if the petshop who said it was okay has steered you wrong before, then you probably should do some research on it. Hope this helps!
Tighebettalover

Onion plants are safe and fine. I never had one, just not that interested in it. I do know that they are easy to grow. You can buy just the bulbs and grow it yourself. Anyway here is a basic profile.

Here is a link that might be useful: Tropica description

Make sure you trim any dead parts off so they do not contaminate the water. Its odd that there are no roots...does the plant look sick? Your fish are probably just weary of it because it is new to their surroundings.

Are you familiar with normal onions? Thsi plant, while not an Onion is similar in habit, the roots will be generated by the bulb, the leaves will be generated by the bulb, so long as there is a firm bulb there (don't bruise it to test it) it doesn't matter if the outer layers are partially rotting/missing so long as the center is still good, the outer layers are just storage for extra sugars, and the fibres are proboly the little strands of fibre left from this very fiberous plant rotting.

If it has started to rot then don't use it in the tank. Trust what you are seeing. If you have fish that's avoiding it then take it out. Work on the side of safety. You didn't mention the size of the tank but a small tank is more apt to get toxic a larger one.

Next time you decide to get an aquatic plant, make sure it looks 'fresh' and not too stale. If it looks like it's been suffering in the store due to incorrect lighting or lack of nutrients - do not buy it.

Ianna

Thank you all for your comments. I'll see if I can get to the heart of any questions in the short time I have.

Ianna- I do indeed have a small tank: 2.5 gallon (and that's an upgrade). I removed the plant shortly after placing it in because I know that even a small amount of rotting material can drastically alter the water chemistry in a short period of time.

As mentioned before, this is my first time dealing with aquatic plants, and since nearly all of the plants in the store had floaters on them I figured that was how they were supposed to be. Even the nice aquatic shop (that charges way too much for me!) has what I now consider "dirty" plants.

the little plant has now been in a separate tiny bowl for a couple of days so I am going to test the water and see if there are any changes. Once I remove all of the material that looks dead, should I replant it in the same pot and sponge material? Will it continue to produce dead material?

Based on appearance, I would have never chosen this little plant, but it was one of only a few that supposedly grew slow enough not to overwhelm my tank too quickly.

That spongy material that is around the bulb or roots of those potted plants... are they all the same? I bought another plant at the same time as this onion and was told it was actually three small plants that could be separated once they matured a little more. Could I reuse the pot and "dirt" from the onion when I separate the other plant (it too is in a small pot with some sort of spongy substrate, but it looks somewhat different)?

Sorry I'm so longwinded. I really do appreciate your comments. I've already learned so much from the people on this forum and look forward to learning about this and many more topics to come.

The "spongy material" in the pots, is it a whiteish, fiber? Almost like a stiff cotton? If so it is rock floss or mineral floss. It is nasty stuff for fish. You should carefully remove it trying not to damage the roots. Rinse the plant well afterward. I usually remove it under running water. That seems to help. It is a great medium for plants to grow but when it deteriorates or if fish pull at it, it will float small particles that iritate fish gills. The fish will ""flash" like it has a parasite. I really am unsure of what the problem is with the plant by your description. To tell you the truth just scrap it. A very suitable plant would be a Java Fern. They do well in almost any water conditions and grow very slow unless you have CO2 injection and high intensity light. I know some one who is in Washington State that sells plants and other things as well as gives good advise. The shipping should be minimal for you since you are close. I bought a few plants from him as well as PMDD (poor mans dosing drops) ferts that are excellent. In fact anyone that has a planted tank I would recomend to use PMDD. It is better to dose only the nutrients you need rather then using a "complete" fert. that has usually way too much phosphorus and way too little potassium. The "trace" pack has iron as well as all other important elements. It is suitable to use with distilled or RO/DI to just get the water to optimum parameters. The nice part is $14 will last a few years. A little overkill for Lexie's small aquarium but well worth it. What really sucks is I had a nice batch of plants that was going up on ebay or other sites, but I goofed and got a blue green algae problem. It should only take a week to clear but I wont sell anything for at least a month after. Thank god the LFS I do sell to haven't had any issues, yet.

Here is a link that might be useful: Plants and Ferts.

Most commonly called Rock wool in hortocultural circles.