Roots extensive, matted. Leaves evergreen, spirally arranged, flaccid, up to 25 em long, gradually tapered to apex, bright green, pale toward base.

Very localized plant growing in water with approximately 100,000 plants growing in 47 ponds having a total area of about 0.4 hectares on the summit of 'Eke, 1,375 m, on West Maui, and 50-100 plants growing on lava rocks forming the stream course on a small site on the east slope of Mauna Kea on Hawai 'i, 850 m. The ponds on 'Eke dry out completely during droughts.

Isoëtes hawaiiensis grows in shallow ponds or streambeds and superficially resembles a rush. This family, genus, and species were first identified in Hawai 'i in 1977, although the plant had been collected as early as 1917.

A probable progenitor of lsoëtes hawaiiensis would have come from the I. taiwanensis complex, a group of high-elevation, cold-water, island species occurring along the western Pacific rim from New Zealand to Taiwan. This progenitor may have been carried to Hawai 'i by a bird during migration.

Isoëtes hawaiiensis may be recognized, in the two locations where it is known, as a submerged to emergent, tufted, grasslike aquatic plant with cormlike rhizomes bearing a cluster of spirally arranged, round, linear, grass-like leaves above and roots below.

Reference: Taylor and Wagner (1993).