Flora of New Zealand Series

Type locality: Selwyn River, near its opening into Lake Ellesmere. Type: CHR, J. Clarke, 27/2/1966, forming grass-like mats on bed of river.

Rhizome either much branched and congested giving rise to short stems and long lvs in dense grass-like mats or less closely branched with longer, sparsely branched stems. Lvs c. 5–30 cm. × 0.3–0.4 mm., dark green, almost filiform and only slightly flattened; apex obtuse, often most minutely denticulate; sheath (1)–2.5–3.5–5 cm. long, auricles narrow. Peduncles to 50 cm. long, us. conspicuously thicker just below fls, becoming spirally coiled as fr. matures. Fls protandrous; carpels us. 8, occ. to 16, rarely < 5. Podogynes slender. Achenes (1.7)–2–(2.7) mm. long, asymmetric, brown; mesocarp thin; endocarp smooth, black, with 2 longitudinal slits opp. to and about on level of top of operculum; beak 0.2–0.3 mm. long. 2n = 18.

DIST.: N., S., Ch.

Lagoons, streams and lakes, from brackish water in estuaries to fresh water at c. 700 m. altitude.

FL. 10–(2). FT. 10–5.

Mason (loc. cit. p. 525) points out that: "R. polycarpa is a most unusual member of the genus in that it grows not only in brackish water but commonly in fresh water also".