Yay! This one should be relatively easy - but who am I to judge?

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In circles I run,
One card I hold may be won.

I reside where seeds are planted,
There is one which grew to Command fellow seeds,
But I am not a seed.
You've seen me many times.

There are two places on this island,
Which share the same name,
It is also where all of the seeds started.

My card? Why, it is a knight,
But unavailable through the average means.

Which card do I hold?
And who am I?

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Think carefully, as I might have thrown you off course a few times.