Flora of New Zealand Series

Fig. 2B

Vigorous aquatic perennial. Stems very fragile, to 1 m long, ± 3 mm diam., branched. Leaves distant below, crowded above, alternate, recurved, stiff, opaque, acute to acuminate, c. 16 × 2 mm, margins minutely toothed. All N.Z. collections have been from female plants. Flowers 1 per spathe in axils of upper leaves; female flowers with filamentous perianth-tube c. 0.25 mm diam., to 6 cm long; perianth-segments pink, 1mm long, transparent, with obvious midnerve; staminodia 3, < styles, transparent, white, toothed at tip; styles 3, 1 mm long, bifid, red-purple.

N. Scattered throughout. S. Occurs sporadically on eastern side. In lakes, rivers, streams and ponds.

(S. Africa)

First record: Mason 1960: 382,389.

First collection: Waiwhetu Stream, Hutt Valley, R. Mason 526, 19.1.1950 ().

FL. 1.

L. major may be distinguished from the related Egeria and Elodea by its alternate leaves. This species was thoroughly established and a major weed problem in some localities before it was recognised in the 1950s as an entity distinct from Elodea canadensis.

Present in waters to a depth of 6 m, L. major has a more restricted distribution and is overall less abundant than Elodea canadensis. In some N. Id lakes it is possible that Lagarosiphon entered into and ± replaced communities of Elodea which had attained their maximum density and were declining in vigour. L. major has not yet reached its potential limit of distribution in New Zealand, and has been found during the last decade in scattered eastern S. Id localities; new findings will certainly be made in both islands in the future.

The weed is established in at least four hydro-electric lakes on the Waikato River, alone or with Ceratophyllum demersum, and in May 1968, it caused temporary cessation of electric power generation through blockage of the intake screens of the Aratiatia hydro-station.

The massive weed-beds of L. Major and their detrimental effects on recreation in two of the main original infestations at Hamilton Lake and Lake Rotorua caused the plant to gain prominence locally under the name "lake weed", and ultimately focussed Government attention on aquatic weed problems on a national basis. In 1961, the Rotorua-based Society for Lake and River Weed Eradication was formed, later to be renamed the Weed Eradication Society, (1962) and the Weed Control Society (1967). The Inter-Departmental Committee for Control of Lakeweed was formed in 1963, to be superseded by the Lakeweed Officials Committee in 1964 and the Officials Committee on Eutrophication in 1970, with broad terms of reference to investigate the aquatic weed problem and natural and man-induced nutrient enrichment of New Zealand waters.