Flora of New Zealand Series

marshwort

Aquatic perennial with branched stolons up to c. 1 m long usually lying just below the water surface; nodes with adventitious roots suspended in water and short-petiolate floating lvs. Basal lvs: petioles to c. 1.75 m long, very slender; lamina floating, 4.5-8.5 × 3.5-7.5 cm, suborbicular or broadly elliptic-ovate, reddish pink or reddish purple beneath, glandular-punctate beneath; margin entire; base deeply cordate with a narrow triangular sinus 2-2.5 cm deep. Fls c. 7 per cluster; pedicels to c. 7 cm long, curving upwards towards apex to carry fls above surface. Calyx 6-9 mm long; lobes lanceolate, obtuse. Corolla medium yellow, 2.5-4 cm diam.; wings of lobes c. 2-3 mm broad, with fimbriae 2-3 mm long. Style short. Stigmatic lobes broad. Capsule < 1 cm long; seeds c. 1.5 mm long, glabrous.

N.: Lake Okareka (Rotorua Lakes District); S.: between Rakaia and Te Pirita.

Victoria, N.S.W. 1985

In still water near lake margin in shelter of sedge, sometimes on mud by water's edge, and in pond fed by irrigation channel.

FL Sep-Nov.

Marshwort has spread rapidly since it was planted in Lake Okareka around 1976 and its dense growth has resulted in mats of floating lvs covering the surface. There are several colonies, of which the largest was c. 20 × 3 m in 1985, and all are derived from the original plantings [Clayton, J. S. and Tanner, C. C., New Zealand J. Bot. 23: 187-190 (1985)]. Seeds have not been reported from N.Z. In Australia they are globose or nearly so and lack fimbriae, i.e. very different from N. peltata above. The lvs of N. geminata greatly resemble those of the unrelated waterlilies, Nymphaea spp., but in addition to the many floral differences there are no thick rhizomes in Nymphoides. Another plant superficially resembling marshwort but even more distantly related is the monocotyledonous Hydrocleis nymphoides (Humb. et Bonpl.) Buchenau, water poppy. However, as well as the even greater floral differences, in water poppy the lvs are in tufts and usually some are partly or completely emergent, whilst the petiole is attached near the lamina margin.