It is very similar in the United States. Apples and pears are labeled by cultivar because typical consumers can readily tell the difference between different cultivars. All cultivars of navel oranges are labeled navel oranges and not distinguished by cultivar. Valencia oranges are sold as Valencia oranges. Lemons are divided into two size classes and sold as large lemons and small lemons and are not distinguished by cultivar. Large seedless limes are sold as limes. They are not sold under their cultivar name although there is only one cultivar of large lime that is generally available. Small seedy limes typically come in mesh bags and are sold as Key limes or Mexican limes. Grapefruit is sold as pink grapefruit or white grapefruit or under a marketing name such as Texas Ruby Red grapefruit which encompasses multiple cultivars. Mandarins are an exception. They are usually sold under their cultivar name or a marketing name such as Cuties or Delite but even those sold under a marketing name often have the cultivar printed on the bag. Minneola tangelos, Meyer lemons and other specialty citrus are sold under their cultivar name when they are available. In general, if a typical consumer can't tell the difference between two different cultivars of a fruit then no distinction is made in the way they are sold.

All produce in the US should have a PLU sticker.

http://xmb.stuffucanuse.com/xmb/viewthread.php?tid=5170

PLU stickers are usually present on grapefruits. But as far as I know, PLU codes are just a description of a fruit type, not the variety...

Here, in the stores the sticker usually will say "Persian lime" or whatever the variety is & also the state or country it came from.

So the tree that is the same still needs to be engrafted?
Anyway, here's my polyembrionic grapefruit:

http://desmond.imageshack.us/Himg19/scaled.php?server=19&filename=dsc00230vb.jpg&res=landing

I guess I won't be able to different these two trees, but I'm sure I will find some help here

Above mentioned method is easier to utilize when there are 3 or more sprouted embryos... In your case (only two embryos) the only way to identify the odd one is to compare it to the mother tree. As I presume the seeds are taken from a store bought grapefruit, there's no way to tell whether it carries mother's genes or not. Obviously you'll have to perform a blind folded guess...

And I need to seperate them, right?

You should've already done it... If you leave the seedlings grow, their roots will get tangled up badly, and you'll end up having lots of fun transplanting them to separate pots. An advice, when transplanting citrus seedlings, pinch their taproot tips to promote root branching, which usually results in more vigorous seedling growth. Good luck!

Take care,
Igor

Polyembryonic means more than 1 seedling grows from 1 seed.
Also, if only 1 seedling from a seed grows, it can be polyembrionic.

Polyembrionic (nuclear) are 100 % from ovary and will come absolut true, if no mutation apeared.

> Polyembryonic means more than 1 seedling grows from 1 seed.
Yes.

> Also, if only 1 seedling from a seed grows, it can be polyembrionic.
No, but it can be nucelar.

> Polyembrionic (nuclear) are 100 % from ovary and will come absolut true, if no mutation apeared.
No, one can be zygotic.

how can that be, if it is 100 % from ovary ?

Polyembryonic means several embryos.
Nucelar means coming from the nucelle (nucellus) . These are clones of the mother plant.

In a polyembryonic seed you have one zygotic (fecundated) seedling _that can abort_, the others are nucelar.

Aha ...

As I learned polyembryonic and nuclear is same.

The original zygotic embryo dies and then the nuclear embryos grow from the overy to replace it.