What exactly is this plant?
 

Could you please help identify? I bought this ages ago at some exhibition or
other, it was called Aster alpellus. Nice, small, spring aster with
beautiful flowers. Not alpinus - it blooms later than those, it is a cross
between alpinus and amellus, hence the name. And now a friend of mine says
that it is tongolensis. As she is rather obstinate, I need some very, very,
very solid facts to convince her that it is not:) Anyone knows the
differences between those two species?

Regards, Barbara.

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