Myriophyllum robustum


Myriophyllum: many leaves
robustum: sturdy

Common Name(s)

Stout water milfoil

Current Conservation Status

2012 - At Risk - Declining

Conservation status of New Zealand indigenous vascular plants, 2012
The conservation status of all known New Zealand vascular plant taxa at the rank of species and below were reassessed in 2012 using the New Zealand Threat Classification System (NZTCS). This report includes a statistical summary and brief notes on changes since 2009 and replaces all previous NZTCS lists for vascular plants. Authors: Peter J. de Lange, Jeremy R. Rolfe, Paul D. Champion, Shannel P. Courtney, Peter B. Heenan, John W. Barkla, Ewen K. Cameron, David A. Norton and Rodney A. Hitchmough. File size: 792KB

Previous Conservation Status

2009 - At Risk - Declining
2004 - Gradual Decline


2012 - Sp
2009 - EF, Sp


Myriophyllum robustum Hook.f.



Flora Category

Vascular - Native

NVS Species Code


The National Vegetation Survey (NVS) Databank is a physical archive and electronic databank containing records of over 94,000 vegetation survey plots - including data from over 19,000 permanent plots. NVS maintains a standard set of species code abbreviations that correspond to standard scientific plant names from the Ngä Tipu o Aotearoa - New Zealand Plants database.

Structural Class

Dicotyledonous Herbs other than Composites


Myriophyllum variaefolium var. beta Hook.f.


Endemic to the North and South Islands. In the North Island known now only from Northland to Taranaki and the northern Rangitikei. In the South Island only known from North West Nelson, the West Coast and Fiordland


Shallow peaty lakes, slow flowing streams, dune ponds, and in muddy or seasonally flooded ground in alluvial forest.


Perennial aquatic herb which if in pools of water is firmly rooted to the bottom. Stems spongy, inflated up to 1.5 m long, emergent portion 300 mm tall, erect to prostrate. Submerged leaves in whorls of (4-)5-7, (15-)20-35 x (4-)6-10 mm finely divided, pectinate with 26-32 pinnae, brown, these diminishing in size toward water surface. Emergent leaves glaucous, tinged red, narrowly ovate to oblong, apex acute, otherwise similar to submerged leaves. Flowers perfect. Sepals 4, ovate to deltoid 0.6-0.8 x 0.5-0.6 mm, petals 4, weakly hooded, 2.5-4 x 1-1.5 mm. Fruits globular to slightly turbinate, 1.5-2 x 2-2.5 mm.

Similar Taxa

Similar to the naturalised M. aquaticum (Vell.) Verdc. From which it differs by being monoecious (males and females on the same plant), the exposed stems usually pink coloured and by the leaf tipes which are acute rather than blunted ended


September - March


October - April

Propagation Technique

Easy in a pond or in permanently damp soils. Can be grown from division of rooted pieces, by cuttings and seed. An attractive plant which should be more widely grown.


Threatened by wetland drainage, eutrophication, and the spread of naturalised wetland weeds.

Chromosome No.

2n = 28

Endemic Taxon


Endemic Genus


Endemic Family


Where To Buy

Can be purchased from Oratia Native Plant Nurseries (info@oratianatives.co.nz).  

Cultural Use/Importance

Myriophyllum robustum is proving popular as an aquarium and pond plant.


Fact Sheet Prepared by P.J. de Lange (1 April 2007). Description based on fresh plants and herbarium material - see also Orchard (1979)

References and further reading

Orchard, A.E. 1979: Myriophyllum (Haloragaceae) in Australasia. 1. New Zealand: a revision of the genus and a synopsis of the family. Brunonia 2: 247-287.

This page last updated on 13 May 2014