Flora of New Zealand Series

Type locality: St John's Lake [Auckland]. Type: Herb. A. Bennett (?), T. F. Cheeseman, Dec. 1881. Isotype: AK 1237.

Rhizome sparsely branched, rooting at nodes and producing mostly simple lfy branches that reach up to surface of water. Stipules membr., free, open. Submersed lvs us. rather distant, us. shortly petiolate; lamina c. 4–6–(10) × (0.5)–1–1.5 cm., elliptic, entire, subacute, delicate and translucent, longitudinal nerves c. 5–(11), joined by irregular cross veins. Floating lvs often long-petiolate; lamina (2)–3–4 × (1)–1.5–2.5 cm., broad oblong-oval, entire, us. quite obtuse, firm and opaque, longitudinal nerves c. 11–(13) in all, laterals emerging from petiole rather than from midrib. Peduncles in axils of floating lvs, stout, erect, us. projecting several cm. above surface of water at fl., submersed in fr. Spike (1)–2–2.5 cm. long, dense. Achene c. 2.5 × 1.5 mm., moderately flattened with rather strongly 3-ridged keel and short straight beak.

DIST.: N., S., St., Ch.

Also recorded in Australia.

Common in and adjacent to quiet waters.

FL.11–2. FT.12–3.

Absolute and proportionate sizes of various parts alter with depth of water; small plants growing and flowering in wet mud without free water lack the distinctive lower lvs. Hagström (K. svenska Vet. Akad. Handl. 55, 1916, 174) named two forms: forma corymboides, with upper internodes 10_17 cm. long and petioles of upper lvs 9_10 cm. long, from "Ponds Nelson, S. Isl., 69, Travers (hb Stockholm et Uppsal.)"; forma frondosus, "a shallow-water form with a couple of branches at the base, short internodes and only coriaceous leaves" from "Hokianga, Ins. bor., 74, Berggren (hb Lund.)"

P. membranaceus Hagström in K. svenska Vet. Akad. Handl. 55, 1916, 157, f. 75 is known only from the original gatherings from running water, Waihi Stream, Waikato, T. F. Cheeseman, –/1/1884, the type being in the Tisellius herbarium in hb Stockholm; isotype: AK 108156. Lvs all membr., short-petioled; lamina c. 6 × 1.5 cm., lanceolate, very shortly mucronate, c. 13-nerved; peduncles long, fl.-spikes to 1.5 cm. long, fr. absent. Later collecting in the Waikato has failed to produce matching plants, and it seems likely that this is an exceptional case of infls appearing among submersed lvs of P. cheesemanii.

P. porrigens Hagström in K. svenska Vet. Akad. Handl. 55, 1916, 172, f. 89 is also known only from the original material "Hokianga, 74, Berggren (hb Stockholm, Uppsal., Lund)." Membr. submersed lvs scarcely petiolate, lamina 5–6 cm. × 3–5 mm., linear-lanceolate, obtuse; floating lvs with an excessively long petiole (10–15 cm.), lamina 1.5–2 cm. × 5–6mm., oblong-lanceolate narrowing gradually to petiole, obtuse, 5–7-nerved; peduncle 10–12 cm., fl.-spike to 1 cm. long; fr. not seen. Hagström considered this distinct from P. cheesemanii "though extremely nearly related to that multiform species". Certainly both forms of lvs described can be matched in undoubted P. cheesemanii.