Isoetes mississippiensis, the Mississippi quillwort, is a small aquatic pteridophyte from the family Isoetaceae.

[1] The species can be found in the southern part of Mississippi in the tributaries of the Pearl River.

Isoetes mississippiensis occurs in persistent, sluggish streams in the southern part of Mississippi.

Other plants that occupy the same habitat include the graminoids such as rushes and panicgrass.

The sporophylls are also spirally arranged and can grow to 40 cm long and 2.0mm wide at the mid-length.