Potamogeton suboblongus Hagstr.

Rhizome little-branched, us. buried in firm mud; lfy branches erect, us. simple, long or short, often rooted at lf-bearing nodes. Stipules c. 2–3 cm. long, free, open, membr. and often conspicuous. Lvs entire; lower lvs apparently not regularly submersed and not clearly distinct from upper lvs though often more narrowly elliptic and with fewer, more obscure nerves; upper lvs long-or short-petiolate, lamina 1.5–6 × 0.8–3.5 cm., broad-elliptic or occ. oval, subacute and sts shortly attenuate at tip, firm and opaque, longitudinal nerves (11)–13–21 in all, us. several laterals emerging from midrib. Peduncles arising in axils of upper lvs, simple, stout, erect, standing well above lvs. Spike 1–2 cm. long, dense. Achene c. 2 × 1.5 mm., neither flattened nor strongly keeled, beak short but slightly curved, ± red when ripe.

Ponds, swamps and boggy places in North, South and Stewart Islands.

Can be grown by cuttings or seedlings.