Bulbostylis capillaris is a species of sedge known by the common names densetuft hairsedge and threadleaf beakseed.

It is an annual herb which is somewhat variable in appearance but generally takes the form of a small, upright tuft of green herbage growing close to the ground, between 10 and 24 centimeters tall.

The inflorescence occurs at the tip of the stem and is composed of tiny spikelets which are green washed with rusty red.

Along with Piptochaetium montevidense and Juncus capillacaeus, Bulbostylis capillaris is used in Rio Grande do Sul as a medicinal plant in the form of a tisane to treat urinary tract infections (UTIs).

This claim of antimicrobial activity against two common causes of UTIs, E. coli and Klebsiella pneumoniae, was investigated by Vogel et al. (2011) but found no evidence of effectiveness in treating bacterial infections.