The Painted Lady (Vanessa cardui) looks very similar to the American Painted Lady (Vanessa virginiensis).
The easiest way to tell them apart is that the American Painted Lady has a tiny white spot in the postmedian area of the forewing (in the orange square area). 
The Painted Lady does not have this with spot.
Also, if you look on the underside of the hindwing, the American Painted Lady has two large eyespots where the Painted lady has four small eyespots.
The American Painted Lady is common in North America and Central America and also in the south of the Iberian Peninsula and on Tenerife.

Also similar is the West Coast Lady (Vanessa annabella), but the Painted Lady has the large white subapical spot near the front edge of the front wing while that of the West Coast Lady is orange a bit larger.
The underside of the wings are very similar, but the eye spots on the hindwing are usually round or oval in the Painted Lady, while at least some are usually heart or kidney-shaped in West Coast Lady. 
The West Coast Lady occurs throughout much of the western US and southwestern Canada.

Falmouth, Maine, USA, 2 August 2015