do i have to mutate the lilia with something special?

Yes, the Mutation Liquid from the Supply Shop.

How do i get the magic plants if i've either used, discarded, sold the original seeds and i do not wish to start over?

Wait to buy more seeds or cross pollinate and save up seeds of those you do have to eventually collect the right plants to do the MP's - Sometimes it is just simpler to start over though. I started the game maybe 5 or 6 times untill I knew enough to finally open a game and really play it!

i'm really confused, i forget what i've crossed with what and how o do it again, i got the rose fern quite by accident and it wasnt until then that i realised what i was supposed to do...

In order to keep track of how to produce the plants, most people keep some sort of records. However, there are quite a few breeding references and utilities in the Plant Tycoon Guides that people have created and submitted to us that you might find helpful.

utilities?

Like electric, water and gas? LOL

In the computer world, utilities are small programs that perform specific tasks.

I bought PT a couple of weeks ago, and the only guide I looked at was the one for the Magic Plants. I like the challenge of figuring things out, and accidentally coming up with solutions! I have to say, I thought I had gotten myself hooked on an extremely complicated game when I saw the posts about charts, graphs and virtual items. But, today I did two things I didn't think were possible, forgive me if this is old news, as I said, I didn't use the spoilers much. I created the last mp I needed by accidentally crossbreeding a Blazing Fern and a Arthurium Tigerfern, which gave me a Venomous Maple, then I crossed the VM with a Citrus Rare Oak, which gave me the Mela Rare Oak.I never had a citrus ball cactus, and thought I read that it could not be created, but later today I crossed a Fabled Lemonbush and a Tillia Multiflora and got a Citrus Ball cactus!!!! I got the components of all the MP's pretty much accidentally!! So, now i can relax about using all my seeds and just see what I create! Fun game!!!!

Congratulations! You've discovered the interesting breeding possibilities that the Tier 4 plants provide. The Citrus Ball Cactus is not required once you have Tier 4 plants available.