why the fern has 480 chromosomes
In adittion to Q's post showing that this is an irelevant point anyway. Plants are capable of polyploidy. This is the ability of having several copies of the same genome. This comes about by having a gamete fertalized more than once. This does have some impact on the ability to reproduce, and sometimes can change their expressed trait. For instance the nice big stawberries that you like to eat so much, have 6 sets of chromosomes. Somehow, the result of these copies are (at least for strawberries) are a bigger fruit.
For this plant to be evaluated any further you have to be slightly more specific than 'fern.'
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"Science without religion is lame; religion without science is blind." - Albert Einstein