Eriocaulon decangulare, commonly known as ten-angled pipewort, hat pin and bog button, is a monocotyledonous plant native to the eastern United States, Mexico and Nicaragua.

This plant is found in peat and sand that is moist to wet, and is associated with savannahs, bogs, pinelands, ditches and the banks of cypress domes.

[3] In the United States it is mainly confined to the Atlantic Coastal Plain, but several significant outlying populations also exist in more mountainous and inland regions.

[3] A study in North Carolina of three inland, mountainous populations found the ten-angled pipewort has a high affinity for acidic soil, ranging from a pH 4.1 to 5.2 in their samples.

The ten-angled pipewort was found to occur with several rare or threatened wetland plants, such as Cleistes divaricata (spreading pogonia), Drosera rotundifolia (round-leaved sundew), Carex trichocarpa (hairy-fruit sedge) and Sanguisorba canadensis (Canada burnet), though these associations differed from site to site.