The New Zealand Plant Conservation Network

Species

Lagarosiphon major

Etymology

major: greater

Common Name(s)

Lagarosiphon

Authority

Lagarosiphon major (Ridley) Moss ex Wager

Family

Hydrocharitaceae

Brief Description

Submerged perennial bottom rooted oxygenweed. It is characterised by strongly recurved leaves along the stem that are arranged spirally and closely-packed, even more so towards the shoot apex. Leaves are dark green and up to 16 mm long and 2mm wide and gradually tapering to an acute tip. The stems are long, slender, brittle and much branched. The flowers are minute, only 0.25 mm in diameter on fine filamentous stems up to 6 cm long found in the upper leaf bases.

Flora Category

Vascular - Exotic

NVS Species Code

LAGMAJ

Structural Class

Monocotyledonous Herbs

Distribution

Widely naturalised in North Island and lowland northern and eastern South island, rare in Westland and upland South Island.

Habitat

Moderately fast flowing to still water bodies. Waters of low fertility, clear streams and lakes.

Features

Vigorous submerged bottom rooting aquatic perennial reaching depths of 6.5m. Stems slender, brittle and much branched. Leaves are dark green, alternate and crowded and overlapping toward the apex of the stem. They are also stiff and curved downwards, are gradually tapered towards the tip, usually 6 to 20 mm long, and have minute marginal serrations. Flowers are tiny 0.25 mm in diameter and up to 6 mm long, pinkish and occur threadlike from the axils of upper leaves. Only female plants have been collected in New Zealand.

Similar Taxa

Canadian pondweed (Elodea canadensis) and egeria (Egeria densa). Both of these species have leaves arranged in whorls on the stem, whereas lagarosiphon has leaves arranged alternately in a spiral pattern and leaves are downward curving.

Flowering

January-March

Flower Colours

Red / Pink

Fruiting

No seed production known in NZ

Year Naturalised

1950

Origin

Africa.

Reason for Introduction

Ornamental pond plant

Control Techniques

Plants can be physically removed from the lake or waterway using SCUBA or snorkel divers for small scale infestations, or using mechanical diggers. But the appropriateness of these methods is site specific, and the potential for contamination of other sites by mechanical equipment is a signficant concern. There are a number of manipulations to the habitat that in theory can control lagarosiphon (e.g., shading, bottom lining, water drawdown) but there are significant limits to their practical application, rendering them site (or waterbody) specific. The only chemical products registered for aquatic use in New Zealand that are efficacious on lagarosiphon are diquat and endothall. Diquat is a relatively fast acting contact herbicide, which interrupts the electron transport system in plant photosynthesis and causes the destruction of cell membranes and desiccation. At present the introduced grass carp (Ctenopharyngodon idella) are the only biocontrol agent available to manage lagarosiphon.

Life Cycle and Dispersal

Perennial. New plants develop from stem fragments which can produce adventitious roots. There is no seed production in New Zealand, with only female plants of this species being present here. Stem fragments are easily dispersed within catchments by water flow. New catchments are colonised by contaminated boats and trailers (occasionally motor cooling water), eel nets, diggers, people liberating fish, and emptying aquaria. Birds are unlikely to be a factor.

Tolerances

Physical damage and grazing results in resprouting from branches and fragments.

This page last updated on 21 Aug 2013