Pterocaulon pycnostachyum, with the common names dense-spike blackroot,[3] fox-tail blackroot or coastal blackroot, is a plant species native to Alabama, Mississippi, North Carolina, Florida, Georgia, and South Carolina.

It can be found in pinelands, ditches, depressions, and fields.

[4][5] Pterocaulon pycnostachyum is a perennial herb up to 80 cm (31 inches) tall.

Stems and the underside of leaves are covered with a thick, white layer of woolly hairs.

Flower heads are crowded into a densely packed spike at the tips of the branches.