Isoetes elatior A.Braun

Large aquatic herb; corm 3-lobed, 10–15 mm wide. Leaves to 50, spirally arranged, erect to spreading, 30–45 cm long, 2–3 mm diam., flexible, bright green; base to 15 mm wide, broadly winged, white; peripheral fibre strands, internal hairs and stomata absent; trans-lacunar diaphragms faintly visible; ligule elongate-triangular, 2–5 mm long; labium broad and short. Sporangia elliptic, to 6 mm long, 5 mm wide, opaque, dark brown; velum absent. Microspores spinose, dark brown. Megaspores Type I, 0.45–0.65 mm diam.; proximal and distal faces covered with small irregular tubercles, drying white.

Occurs among rocks or in mud or sand in slow-to fast-moving rivers.