Corm 3-lobed, 5–13 mm wide, bud scales absent. Leaves 12–38, 20–25 x c. 3 mm at base, gradually tapering to a slender point. Ligule not seen. Velum rudimentary to absent. Megasporangia c. 5 × 2.5 mm, ovate, sporangial wall pale; megaspores c. 560 × 480 µm; proximal face trilete, densely pustulate, with densely large and small pustules, sometimes anastomosing, 48–60 µm in diam., wax-like structures sometimes rodlet-like and filiform threads on pustules and dense threads between pustules, larger pustules partly anastomosing, ridges also partly pustulate, up to 60 µm wide and 60 µm high; distal face densely pustulate with large and smaller intermixed pustules, large pustules 45–57 µm in diam., partly anastomosing, small pustules 30–38 µm in diam., pustules almost completely covered with dense threads, sometimes rodlet-like. Microspores not seen.

Isoetes hallei differs from I. alstonii and I. schweinfurthii by the stouter habit, much shorter leaves and slightly larger megaspores.

hallei: after Francis Hallé (born 1938), who first collected this fern at the Zongo waterfalls, Kasangulu, D.R.C.

On wet rocks in waterfalls, c. 320 m.

See African distribution.

Dem. Republic of Congo.

Terrestrial.