I see no parentheses anywhere and I see only one apostrophe. If you are looking to put an apostrophe after the closing single inverted comma, then it is OK punctuation-wise, but of course it is a little hard to decipher, and since a flower is an inanimate object, which normally does not take the Anglo-Saxon possessive anyway, I suggest that you recast for better style: The foliage of Petunia 'Sparklers' is unusual.
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