PARIS — Despite recent optimism that Europe’s economy is finally turning a corner, a stark reality remains: The situation is still fragile.

By many accounts, the euro zone has been rebounding from a wrenching double-dip recession that began in 2008 after the fall of Lehman Brothers. Financial markets have been in a celebratory mood, driving down borrowing costs for even the most troubled economies in recent months, while politicians have declared the worst of the crisis is over.

But the uneven nature of the recovery — between a group of strong countries in the north and a larger swath of weak nations in the southern rim — has made it difficult for the overall economy to gain momentum.

Growth in the currency union rose 0.2 percent in the first quarter, which translates to an annual growth rate of 0.8 percent, according to data released on Thursday by Eurostat, Europe’s statistics agency. While it was the fourth straight quarter of expansion, it was half what economists expected.