Vernonia lettermannii, the narrowleaf ironweed, is a plant species known only from Arkansas and Oklahoma. It grows on floodplains and terraces at elevations of 100–200 m (330–660 ft).

Vernonia lettermannii is a perennial herb up to 60 cm (24 in) tall. Leaves are filiform (thread-shaped), up to 9 cm (3.5 in) long but less than 3 mm (0.12 in) wide. Flower heads are purple, arranged as a corymb.

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