Flora of New Zealand Series

Cape Pondweed

Freshwater, scapose aquatic; tuber globose, 3-4 cm diam., with ring of long, soft roots and fibrous remains of petioles. Leaves submersed and linear, or floating with ± oblong lamina, 10-15-(25) × 3-4-(7) cm, cross-veinlets numerous, very faint; petiole varying in length with depth of water. Inflorescence white, terminal, of 2 divergent spikes exserted just above surface of water, each spike c. 6 cm long, enlarging in fruit; spathe tubular, caducous. Flowers sessile, more or less in two rows, fragrant, seated at bases of white, oblong, bract-like lateral extensions of the spike axis, each segment ± 1cm long, delicate at flowering, becoming larger, reddish and firmer at fruiting. Follicles 3-6, flask-shaped, ±1 cm long. Seeds ± 9 mm long, with green spongy outer testa.

N. Throughout in coastal and lowland areas, not detected in central N. Id. S. Marlborough - Blenheim; Canterbury - near Lake Coleridge, Darfield, Ohoka, Hororata, common at Temuka; Westland - scattered, buy heavy infestation at Lake Mahinapua; Otago - near Dunedin; Fiordland - near Lake Te Anau. In still and slow waters.

(S. Africa)

First record: Kirk 1870: 143.

First collection: Waimate, Bay of Islands, R. Mair, no date ().

FL. 12.

A. distachyus, with its broad, long-petiolate leaves, could be confused with Hydrocleys nymphoides and Ottelia ovalifolia, but may be recognised by the distinct basal tuber with crown of roots, and the terminal inflorescence of 2 divergent many-flowered white spikes.

Cape pondweed is established and often a nuisance in stock water dams and ponds, impeding water flow in slow-moving streams and drainage channels. At Lake Mahinapua, Westland, where it is thoroughly established, it adversely affects recreation - power boating, swimming and fishing. Its presence in localities such as Hororata and near Dunedin show that it will tolerate cold winter conditions and could become more widespread in Canterbury and Otago. Although A. distachyus is very distinct from Eichhornia crassipes and Nymphaea spp. [Nymphaeaceae] and should not be confused with them, it is often erroneously given their respective common names "water hyacinth" or "water lily".

Fig. 5. Aponogeton distachyus, Cape pondweed; A inflorescence of two divergent spikes, B flower with swollen perianth-segment, C leaf. © All rights reserved. [Image: 26XK]