Concern At Spread Of Weed In Streams

Press, Volume CIX, Issue 32252, 21 March 1970, Page 8

Concern At Spread Of Weed In Streams

An aquarium plant of South American origin, Myriophyllum brasiliense, commonly known as parrot’s feather, has spread into drains and other waterways in New Zealand. It is now a problem in some districts, and the Botany Division of the Department of Scientific and Industrial Research is trying to find out more about its present distribution. The weed, a native of eastern regions of South America, has been grown in fish ponds for many years, and has become established in several other countries, including the United 'States, France and Australia. The first report of its growing wild in New Zealand was in Palmerston North in 1929. It has remained in ponds and lagoons in that I area to the present time, but lately it has begun to spread further, and to clog drains and floodways. Last year it was also found in the Aka Aka district north of the Waikato River, and in the Otara Stream near Auckland, and a few years ago a patch of it was found in the Ohau Channel between Lakes Rotorua and Rotoiti. Miss R. Mason, of the Botany Division, has identified the weed and surveyed its incidence in the Manawatu.

She says the division wants to find out how widely it has spread in the wild, what sorts of places it is growing in, how it got to them, and how long it has been established.

“We’d be very glad to receive information, and dried or pressed specimens, from people who think they have the weed but are not certain,” she says. Such information should be addressed to the Director, Botany Division, D.5.1.R., Private Bag, Christchurch. Myriophyllum brasiliense is taller and more robust than most water plants in New Zealand. Its stems can be a quarter-inch thick and Bft long, and they reach stiffly above water for a foot or so The leaves have a comblike appearance, being divided into 13 to 15 narrow! segments. They are an) unusually light green in col ) our, though sometimes the underwater leaves are al reddish brown.

The plant grows in water up to 9ft deep, but it can grow in very shallow water;

or even in damp soil where fragments have been thrown up on to banks and have taken root among sheltering grasses.

It spreads by means of creeping rhizomes in the silt of stream beds, or by broken fragments being washed downstream. Quite small fragments can send out roots and grow. Only female plants are known to exist in New Zealand, so it does not spread by seeding. There is a native species, Myriophyllum robustum, that is very similar in appearance, but this usually grows in swamps where there is a fair amount of dark, brackish water, whereas Myriophyllum brasiliense thrives only in silty conditions.