That Eagle isn't that ugly. Maybe the Stuka had the largest wing area of a single piston engined plane, it's wings were wide. I don't know, I'm just guessing.
I don't know of a single engine aircraft with a larger wing area. The Stuka had 343 sq.ft. but the Hellcat was close at 334 sq. ft. For comparision, the P-47 had only 300sq. ft. and the P-38 was 327 sq. ft.
I think the Ju-87 might take it. The 109 had a wing area of 174 sq.ft. The Hurricane had 257sq.ft. So the Stuka has a quite large wing area. 9 ft larger than the Hellcat.