When I bought some plants from petsmart they had small round leaves, now all of the new leaves that have grown since being in my tank are much larger, but very oddly shaped. What would cause this? Is it a problem?

I'm not complaining about it, I think it looks pretty cool, just want to make sure my tank isn't deficient in any thing.

Not a problem. It has to do mainly with varying light levels I believe. I have 4 heavily planted tanks with CO2 and they all have didn't levels of light. They all share some of the same plants. Some seem unaffected by the difference, but others can have subtle differences in the way the leaves look...wider, flatter, etc..

Thanks for the quick response, just started using ferts and diy co2, wanted to make sure I wasn't killing plants.

The plant you have is water wisteria and I was very confused by this phenomenon too! When I bought the plants some had the lacy leaves and some were rounded. The nut jobs at PetSmart told me they were two different varieties of wisteria. Showed what a noob I am when I mentioned in chat that I had "both types of wisteria". LOL I was told that the rounder leaves grow when the plant grows out of the water, and the fern-like leaves grow when the plant grows under water, but that is just what I was told and perhaps what Ben said is more accurate. At any rate, this phenomenon is just another way that aquatic plants are so cool and why I love planted freshwater tanks.

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10 g planted community, 10 gallon danio/RCS tank, 10 g ghost shrimp grow out tank, 10 g blue pearl shrimp tank, 75 g in the works.

That makes a lot of sense too, because these plants were living in those plastic tubes full of humid air. I think the light plays a role too, because the "laciest" leaves are in the highest light areas.

I have to say, I think I'm having more fun with the plant side of the aquarium hobby than the fish!

Cadiedid is right, but more correctly, What that there is a type of hygro called hygrophila difformis. And the leaf morphing is part of how the plant grows dependant on its surroundings (as its latin name describes...) The warmer the water, the longer thinner and more pointed the leafs become! And you will most likley notice this (as you mentioned) towards the top of the plant, one fun thing to do is to cut the plant off as it nears the top of the tank, strip down the three sets of shoots closest to the bottom, and replant them and take a gander. within days new roots will have shot out, and the chopped tops on the old shoots will already be growing.

This is a phenominal plant to use in starting tanks as you can hardly kill it... and with the ability to morph like it has it can provide a number of cool scapes for different tanks all from one parent plant!

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When you pay that cash or swipe that card you are making a bond with that animal that you will treat it with love and respect, and its needs will be met, first and foremost (unless you have kids...) I don't care if you have to eat ramen noodles or nothing at all to feed your cat dog fish rat whatever. That's the bond you made! Life is precious!

plants in each of my tanks take on different looks too. kinda cool how one condition can change it

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"Being ignorant is not so much a Shame, as being unwilling to learn".-- Benjamin Franklin