Fimbristylis cymosa, commonly known as tropical fimbry, or St. John's sedge, is a sedge of the family Cyperaceae. It has a wide distribution in tropical and subtropical regions of the Americas, sub-Saharan Africa, Asia, Australasia, and the Pacific.

The rhizomatous perennial grass-like or herb sedge typically grows to a height of 0.25 to 0.8 metres (1 to 3 ft). It blooms between February and September and produces brown flowers.

In Western Australia it is found near the coast, on dunes and behind mangroves in the Kimberley region where it grows in sandy-clay alluvium around basalt or sandstone rocks.