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Manual of the New Zealand Flora.
2. Potamogeton, Linn
2. Potamogeton, Linn.
Perennial aquatic herbs. Stems slender, simple or branched. Leaves wholly submerged and translucent, or floating and opaque, alternate or opposite, entire or toothed; stipules intrafoliar, free, or adnate to the petiole or base of the leaf. Flowers small, green, hermaphrodite, ebracteate, sessile in a dense spike on an axillary peduncle arising from a membranous spathe. Perianth-segments 4, small, herbaceous, concave, valvate. Stamens 4, inserted at the base of the segments; anthers sessile, 2-celled, extrorse. Carpels 4, sessile, distinct, 1-celled; stigma oblique, decurrent; ovules solitary, affixed to the inner angle of the cell, campylotropous. Eipe carpels or drupelets 4, small, coriaceous or spongy, ovoid or subglobose, obtuse or beaked by the recurved persistent stigma, 1-seeded. Seed curved, reniform; testa membranous; embryo with a large radicle and narrow incurved cotyledon.
A genus widely spread in the fresh or brackish waters of almost all tem-perate or subtropical regions, more rare in the tropics. Species variously esti-mated at from 40 to 100 or more, according to the different views of authors, extremely variable, and most difficult of discrimination. The New Zealand forms have never been carefully sought for, and in all probability other species will be added to those described herein.
A. Floating leaves more or less coriaceous, with a broad long-petioled lamina, different in shape from the membranous submerged ones. Stipules free.
Floating leaves 2–4 in., biplicate at the base. Submerged leaves wanting or reduced to phyllodes. Fruit large, ⅙ in. long, keeled on the back when dry 1. P. natans. Floating leaves 1–3 in., not plicate at the base. Sub-merged leaves few, linear-lanceolate. Fruit small, 1/12–1/10 in., rounded on the back 2. P.polygonifolius. Floating leaves ¾–1¾ in. Submerged leaves numerous, 2–4 in. Fruit small, 1/10 in., keeled on the back when dry 3. P. Cheesemami. B. Leaves all submerged and uniform, sessile, membranous.
Leaves 1–4 in. by ⅛–¼ in., linear-ligulate, obtuse; stipules free, lacerate. Spike dense 4. P. ochreatus. Leaves 2–4 in. by 1/20–1/15 in., very narrow-linear or filiform; stipules adnate. Spike interrupted 5. P. pectinatus.
| 1. | P. natans, Linn. Sp. Plant. 126. — Stems creeping below, long or short, simple or sparingly branched, terete. Floating leaves on long petioles; lamina 2–4 in. long, oblong or elliptic or elliptic-lanceolate, acute or subacute, subcordate and shortly biplicate at the base, coriaceous, 20–30-nerved with copious cross-veins and page 749minute areolation; stipules very long and conspicuous, 3–5 in., free, acuminate. Submerged leaves wanting or if present few and reduced to long and narrow phyllodes without any lamina. Peduncles stout, 2–4 in. long, bearing a dense-flowered spike 1½–2 in. long. Perianth-segments broadly rhomboidal. Fruit ⅙ in, long, turgid, obliquely ovoid, keeled on the back when dry, beak short.—Hook. f. Fl. Nov. Zeal. i. 236; Handb. N.Z. Fl. 278; Benth. Fl. Austral. vii. 170 (in part); A. Bennett in Journ. Bot. xxv. (1887) 177.
North and South Islands: Probably not uncommon. A widely dispersed plant, found in nearly all temperate climates. Its exact distribution in New Zealand is not yet made out with certainty, as P. Cheese-manii has been recorded in mistake for it in many localities, but I have seen, specimens from both Islands. |
| 2. | P. polygonifolius, Pourr. in Mem. Acad. Toul. iii. (1788) 325.—Stem creeping at the base, long or short, simple or sparingly branched. Floating leaves on long petioles; lamina 1–3 in. long, elliptic-oblong to lanceolate, acute or obtuse, rounded or subcordate or acute at the base, not plicate, thinly coriaceous; stipules much shorter than in P. natans, 1–1½ in. long. Submerged leaves linear-lanceolate, acute. Peduncles variable in length, rather slender; spike dense-flowered, ¾–1½ in. long. Perianth-segments transversely elliptic. Fruit small, reddish, 1/12–1/10 in. long, blunt and rounded on the back, not keeled, beak very short.—Kirk in Trans. N.Z. Inst. iii. (1871) 165.
North and South Islands, Stewart Island: Ponds and small streams-from the North Cape southwards, not uncommon. Sea-level to 1500 ft. December–April. Distinguished from P. natans by the smaller and more membranous leaves, much shorter stipules, slender peduncles, and much smaller fruit not keeled on the back when dry. Several of my specimens have been examined by Mr. A. Bennett, of Croydon, whose knowledge of the genus is unrivalled, and he informs me that their identity with P. polygonifolius cannot be questioned. The species is widely spread in Europe and Asia, and has been recorded from Australia. |
| 3. | P. Cheesemanii, A. Bennett in Journ. Bot. xxi. (1883) 66.—Stems slender, striated, long or short, simple or branched. Upper leaves alternate or opposite, long-petioled; lamina ¾–1¾ in. long, elliptic-oblong to oblong or lanceolate, obtuse, rounded at the base, coriaceous, 10–16-nerved with numerous cross-veins and minute areolation; stipules broad, subacute. Submerged leaves numerous, usually alternate but sometimes opposite, shortly petioled, 2–4 in. long, ¼–¾ in. broad, oblong-lanceolate to lanceolate or linear, very thin and membranous, translucent, 5–12-nerved with rather distant cross-veins, margins often undulate or crisped, not denticulate. Peduncles variable in length, rather slender; spike dense, ½–¾ in. page 750long. Perianth-segments rhombic-orbicular. Fruit small, about 1/10 in. long, broadly ovoid, slightly compressed, keeled on the back, beak short.—A. Bennett, l.c. xxv. (1887) 177; Cheesem. in Trans. N.Z. Inst. xvi. (1884) 410. P. heterophyllus, Hook. f. Handb. N.Z. Fl. 279, 742 (not of Schreber). P. natans var. australis, Kirk ex A. Bennett in Journ. Bot. xxv. (1887) 177.
North and South Islands, Stewart Island: Abundant throughout in streams, ponds, and lakes. Sea-level to 3000 ft. Manihi. November–March. The most abundant species, universally distributed throughout the colony. The numerous submerged leaves and smaller floating ones at once separate it from P. natans, to say nothing of other differences. According to Mr. Bennett, it is also found in Tasmania. |
| 4. | P. ochreatus, Raoul, Choix, 13, t. 7.—Stems slender, striate, branched, long or short according to the depth of the water. Leaves all submerged, alternate or the upper opposite, sessile, 1–4 in. long, ⅛–¼ in. broad, linear-ligulate, obtuse or emarginate at the tip, membranous, 3- or 5-nerved with or without finer parallel veins between, transverse veins few; stipules free, at length conspicuously lacerate. Peduncles stout, erect, usually shorter than the leaves, 1–3 in. long; spike short, oblong, about ½ in. long. Fruit broadly obliquely ovoid, subcompressed, 1/10 in. long, back rounded, beak short, thick.—Hook. f. Fl. Nov. Zel. i. 236, and ii. 336; A. Bennett in Journ. Bot. xxv. (1887) 178. P. gramineus, Hook. f. Handb. N.Z. Fl. 279 (not of Linn.). P. obtusifolius, Benth. Fl. Austral. vii. 172 (not of Mert. and Koch).
North and South Islands: Rivers and lakes from the North Cape to Otago, not uncommon. November–March. This is a much larger and stouter plant than the northern P. obtusifolius, to which it was referred by Bentham. It appears to be plentiful in Australia, ranging from Queensland to Tasmania. |
| 5. | P. pectinatus, Linn. Sp. Plant. 127.—Stems long, filiform, much branched, often forming dense masses. Leaves all sub- merged, alternate, sheathing at the base, 2–4 in. long by 1/20–1/25 in. broad, very narrow-linear or almost filiform, upper channelled on both surfaces, lower flatter, 1–3-nerved with transverse veinlets; stipules adnate with the sheathing base of the leaf. Peduncles long, slender, filiform, not thickened upwards; spike 1½–2 in. long, of distant whorls of flowers. Fruit rather large for the size of the plant, about ⅛ in. long, turgid, obscurely keeled on the back, slightly convex in front, rugose when dry, beak very short.—Hook, f. Fl. Nov. Zel. ii. 336; Handb. N.Z. Fl. 279; Benth. Fl. Austral. vii. 173; A. Bennett, Journ. Bot. xxv. (1887) 178.
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North Island: Auckland—Waikato River and Lake Whangape, Kirk! T. F. C.; Lakes Tarawera and Rotomahana, Kirk! Hawke's Bay—Tangoia Lagoon, Colenso, A. Hamilton! South Island: Canterbury—Lake Forsyth, Kirk! Otago—Lake Waihola, and still waters of the Taieri Plain, Petrie! December–March. A very widely distributed plant, found in fresh or brackish waters in most, parts of the world. |