Isoetes × eatonii, or Eaton's quillwort, is a hybrid between I. engelmannii and I.

[1] It can be found in ponds and slow moving rivers in Canada or in several New England states.

[2] In the United States, it has been found in Pennsylvania, New Jersey, and New York.

The velum covers a sixth to a quarter of the sporangium.

The flattened white megaspores are 320 to 530 micrometers in diameter and bear short spiny ridges.