M. elatinoides, Gaud. in Ann. Sci. Nat. Ser. i. 5 (1825) 105.—Forming dense masses in still waters. Stems slender, 6 in. to 3 ft. long according to the depth of the water. Submerged leaves in whorls of 4, rarely more, deeply pectinately pinnatifid, the segments capillary; the upper emerged or floral leaves in whorls of 4 or 3, sometimes opposite, much smaller, ⅕–⅓ in. long, ovate or oblong to broadly lanceolate, sessile, obtuse, entire or the lower slightly toothed. Male flowers: Calyx-lobes very minute. Petals 4, oblong. Stamens 8. Females: Calyx-lobes and petals apparently wanting. Nuts 4, small, oblong, smooth.—Hook. f. Fl. Nov. Zel. i. 63; Handb. N.Z. Fl. 66; Benth. Fl. Austral. ii. 487; Kirk, Students' Fl. 150.

North and South Islands, Stewart Island: Common in rivers and lakes from the Auckland Isthmus southwards, ascending to 3500 ft. November–February. Also in Australia and extra-tropical South America.

Subalpine specimens are stouter, with less delicate and more closely set submerged leaves, and the nuts are rather larger.

M. intermedium, D.C. Prodr. iii. 69.—Very variable in habit: in lakes and rivers forming masses of floating stems 1–4 ft. long, with numerous submerged leaves; in wet ground sometimes only an inch or two high, with the leaves all linear and entire. Leaves in whorls of 3–8, usually 4–5; submerged leaves deeply and finely pectinately pinnatifid, segments capillary; upper emerged or floral leaves much smaller, ¼–½ in long, lanceolate and inciso-pinnatifid to narrow-linear and quite entire. Male flowers: Calyx-lobes evident. Petals white. Stamens 8. Female flowers: Calx-lobes and petals apparently wanting. Nuts 4, very small, linear-oblong, usually minutely scabrid or almost echinate, rarely quite smooth.—M. variæfolium, Hook. f. in Hook. Ic. Plant. t. 289; Fl. Nov. Zel. i. 64; Handb. N.Z. Fl. 66; Benth. Fl. Austral. ii. 487; Kirk, Students' Fl. 150. M. propinquum, A. Cunn. Precur. n. 532.

North and South Islands, Stewart Island: Abundant in lakes and streams, wet swamps, &c, from the North Cape southwards, ascending to 3000 ft. December–March. Also in Australia, Malaya, and India.

M. robustum, Hook. f. Handb. N.Z. Fl. 67.—Stems stout, erect, branched at the base, 6 in. to 2 ft. high, rarely more. Leaves page 152usually 5 in a whorl, 1–2 in. long, all deeply pectinately pinnatifid; upper rather coarse, usually crowded and overlapping; submerged, leaves not often seen, when present with longer capillary segments. Flowers rather large, ⅕–¼ in. long, solitary or rarely in pairs in the axils of the floral leaves, with a pair of minute laciniate bracts at the base of each. Calyx-lobes present in both sexes, deltoid, jagged. Petals in the males only, linear-oblong. Stamens 8. Stigmas usually 4, plumose. Nuts 4, ⅛ in. long, laterally compressed, usually with a single or double row of tubercles down the back, but sometimes smooth and rounded.—Kirk, Students' Fl. 151. M. variæfolium var. b, Hook. f. Fl. Nov. Zel. i. 64.

North Island: In swamps from Ahipara to the Upper Waikato, but often local; apparently rare further south. Hawke's Bay, Colenso! Mungaroa, Wellington, Kirk! South Island: Awatere, Kirk! Moutere, Nelson, T. F. C.; near Westport, Townson! Hokitika, Tipler. December–February.

This is seldom found in lakes or streams, and is a marsh plant rather than a true aquatic. It often covers large stretches in swamps that are quite dry in. summer.

M. pedunculatum, Hook. f. Fl. Tasm. i. 123, t. 23B.—Stems short, simple or sparingly branched, tufted, 1–3 in. high, usually forming broad matted patches. Leaves opposite, minute,. ⅛–¼ in. long, linear or linear-spathulate, quite entire, rather fleshy. Flowers minute, usually diœcious; males shortly stalked or sessile;. females sessile; bracts 2 at the base of each flower, minute, linear. Calyx-lobes 4, very minute. Petals 4, wanting in the female flowers. Stamens 8. Stigmas 4, plumose, recurved. Carpels 4, small, oblong, minutely rugose.—Handb. N.Z. Fl. 67; Kirk, Students' Fl. 151.

North and South Islands, Stewart Island: From Cape Maria van. Diemen southwards, but far from common. Sea-level to 2000 ft. December–February. Also in Australia and Tasmania.

M. verrucosum, Lindl. in Mitch. Trop. Austral.; Benth. Fl. Austral. ii. 488, is included by Mr. Kirk in the "Students' Flora" as a native of New Zealand, on the authority of specimens gathered by himself near Tauranga Harbour. These are very imperfect, having no flowers and few withered fruits; but, having compared them with authentic examples of M. verrucosum from Australia, I can state definitely that they are not referable to that species. They only differ from M. intermedium in the upper leaves being pinnatifid, and until more complete specimens are obtained are best considered as a form of that plant.