Ruppia polycarpa


Ruppia: Named after Heinrich Bernhard Ruppius (1689-1719), an 18th century German botanist

Common Name(s)

horses mane weed, lakeweed

Current Conservation Status

2012 - Not Threatened

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 - Not Threatened
2004 - Not Threatened


Ruppia polycarpa R.Mason



Flora Category

Vascular - Native

Structural Class

Monocotyledonous Herbs




Indigenous. North, South and Chatham Islands. Also in Australia


Saline ponds, lagoons, brackish streams, slow flowing fresh water streams and fresh water lakes from sea level to 700 m a.s.l.


Rhizome prominent, and either much branched and congested giving rise to short stems and long leaves in dense grass-like mats or less closely branched with longer, sparsely branched stems. Leaves c.50–300 × 0.3–0.4 mm, dark green, almost filiform and only slightly flattened; apex obtuse, often most minutely denticulate; sheath (10-)25–35–50 mm long, auricles narrow. Peduncles to 0.5 m long, usually conspicuously thicker just below flowers, becoming spirally coiled as fruit matures. Flowers protandrous; carpels (5-)8(-16). Podogynes slender. Achenes (1.7-)2(-2.7) mm long, asymmetric, brown; mesocarp thin; endocarp smooth, black, with 2 longitudinal slits opposite to and about on level of top of operculum; beak 0.2–0.3 mm long.

Similar Taxa

Ruppia polycarpa differs from R. megacarpa by its curved to straight rather than zig-zagged branching pattern, obtuse rather than bidentate leaf apices; carpels usually 4 per flower (rather than (5-)8(-16)), and fruits which are 4-5 mm long rather than < 3 mm long. Stuckenia pectinata which sometimes grows with both species of Ruppia is superficially similar. It is easily distinguished from both Ruppia species by the ligulate acute-tipped leaves, tuberous stems, and spicate inflorescences.


October - February


October - May

Propagation Technique

Uncertain. Probably easily grown in suitable conditions but Ruppia is unlikely to be widely cultivated (if at all). Most people regard it as a pest and are only interested in eradicating it.


Not Threatened

Chromosome No.

2n = 18

Endemic Taxon


Endemic Genus


Endemic Family


Where To Buy

Not commercially available


Fact sheet prepared for NZPCN by P.J. de Lange 2 March 2011. Description adapted from Moore & Edgar (1970).

References and further reading

Moore, L.B.; Edgar, E. 1970: Flora of New Zealand Vol. II. Wellington, Government Printer. 

This page last updated on 11 Aug 2014