Adults: Like the painted lady (V. cardui), this is an orange and black butterfly with white spots on the dark forewing tips and white cobwebbing on the brown underside of the hindwing. The American lady, however, has a somewhat concave or "notched" outer edge of the forewing. Also, there are 2 large (not 4 small) eyespots on the underside of the hindwing. Seen from above, the wide dark median forewing band is broken into two parts, without a connecting bar. The upperside hindwing spots are very close together, often with a somewhat smeared appearance; the first spot (not counting a smaller spot that can sometimes be before it) is noticeably larger than the others. American ladies also frequently have a small white spot in the orange field near the edge of the forewing, seen from above.
Larvae: Black with yellowish crossbands, black spines, and white spots on the sides of the abdominal segments; head black.
Similar species: The painted lady (V. cardui) is very similar. The easiest way to tell them apart is the eyespots on the underside of the hindwing: American lady has 2 large ones, and painted lady has 4 small ones.