Stout perennial herb; stems to 30 cm tall, prostrate to erect. Lvs all whorled, slightly dimorphic. Submerged lvs often decaying early, in whorls of 5–7. Aerial lvs yellow-green to subglaucous, crowded towards tips of stems, spreading, in whorls of (4)–5–7, oblong, (15)–20–35 × (4)–6–10 mm, becoming smaller near water surface, pectinate, with 26–32 filiform to linear pinnae. Fertile aerial lvs similar to other lvs. Fls ☿. Bracteoles ovate to orbicular, 0.7–0.8 × 0.7–0.8 mm. Sepals 4, ovate to deltoid, 0.6–0.8 × 0.5–0.6 mm; petals 4, weakly hooded, 2.5–3.4 × 1.1–1.2 mm. Frs globular to slightly obturbinate, 1.5–2 (excluding sepals) × 2–2.5 mm, with a few small tubercles on keel of mericarps.
[From: Webb et al. (1988) Flora of New Zealand. Volume 4.]
Flowering: Oct.–Mar.; Fruiting: Oct.–Mar.