Ruppia polycarpa
Common names
Horses mane weed, lakeweed
Biostatus
Native
Category
Vascular
Structural class
Herbs - Monocots
Detailed description
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.
Distribution
Indigenous. North, South and Chatham Islands. Also in Australia
Habitat
Saline ponds, lagoons, brackish streams, slow flowing fresh water streams and fresh water lakes from sea level to 700 m a.s.l.
Current conservation status
The conservation status of all known New Zealand vascular plant taxa at the rank of species and below were reassessed in 2022-2023 using the New Zealand Threat Classification System (NZTCS) – more information about this can be found on the NZTCS website. This report includes replaces all previous NZTCS lists for vascular plants. Previous assessments can be found here.
Please note, threat classifications are often suggested by authors when publications fall between NZTCS assessment periods – these interim threat classification statuses has not been assessed by the NZTCS panel.
- Conservation status of vascular plants in Aotearoa New Zealand, 2023. 2024. Peter J. de Lange, Jane Gosden, Shannel P. Courtney, Alexander J. Fergus, John W. Barkla, Sarah M. Beadel, Paul D. Champion, Rowan Hindmarsh-Walls, Troy Makan and Pascale Michel Department of Conservation. Source: NZTCS and licensed by DOC for reuse under the Creative Commons Attribution 4.0 International licence.
2023 | Not Threatened | Qualifiers: SO
Detailed taxonomy
Family
Ruppiaceae
Synonyms
None
Endemic taxon
No
Endemic genus
No
Endemic family
No
Ecology
Flowering
October - February
Fruiting
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.
Wetland plant indicator status rating
Information derived from the revised national wetland plant list prepared to assist councils in delineating and monitoring wetlands (Clarkson et al., 2021 Manaaki Whenua – Landcare Research Contract Report LC3975 for Hawke’s Bay Regional Council). The national plant list categorises plants by the extent to which they are found in wetlands and not ‘drylands’. The indicator status ratings are OBL (obligate wetland), FACW (facultative wetland), FAC (facultative), FACU (facultative upland), and UPL (obligate upland). If you have suggestions for the Wetland Indicator Status Rating, please contact: [Enable JavaScript to view protected content]
OBL: Obligate Wetland
Almost always is a hydrophyte, rarely in uplands (non-wetlands).
Other information
Where To Buy
Not commercially available
Etymology
ruppia: Named after Heinrich Bernhard Ruppius (1689-1719), an 18th century German botanist
Chromosome number
2n = 18
Previous conservation statuses
2017 | Not Threatened | Qualifiers: SO
2012 | Not Threatened
2009 | Not Threatened
2004 | Not Threatened
Referencing and citations
References and further reading
Moore LB, Edgar E. 1970. Flora of New Zealand, Volume II. Indigenous Tracheophyta: Monocotyledones except Gramineae. Government Printer, Wellington, NZ. 354 p.
Attribution
Fact sheet prepared for NZPCN by P.J. de Lange 2 March 2011. Description adapted from Moore & Edgar (1970).
Some of this factsheet information is derived from Flora of New Zealand Online and is used under a Creative Commons Attribution 3.0 New Zealand licence.
NZPCN Fact Sheet citation
Please cite as: de Lange, P.J. (Year at time of access): Ruppia polycarpa Fact Sheet (content continuously updated). New Zealand Plant Conservation Network. https://www.nzpcn.org.nz/flora/species/ruppia-polycarpa/ (Date website was queried)