Althenia bilocularis
Biostatus
Native
Category
Vascular
Structural class
Herbs - Monocots
Detailed description
Annual, summer-green, submerged, rhizomatous herb forming small patches. Stems up to 20 cm long, thread-like, usually unbranched. Internodes 1-4 cm long. Leaves regularly alternate, leaf-base at first sheathing stem, to 4 mm long, becoming fibrous with age, leaf-blade 2.5-3.5 x 1 mm, entire, 1- or 3- nerved, with nerves extending to the squarely truncate tip. Flower enclosed within leaf-bases. Both sexes in separate positions on the same plant. Male on small 5 mm stalk (pedicel), stamen solitary, anther 2 x 0.6 mm, sickle-shaped, with 2 pollen sacs. Female shortly stalked (pedicellate), perianth-segments narrow-oblong, lacerate, 1.5 x 0.5 mm. Carpels 3(-4), style narrower than ovary, stigma funnel-shaped with long feathery margins. Seed (achene) 1.5-2 x 0.5 mm., asymmetrically oblong, yellow, smooth, narrowing above to style remnant c. 1 mm long.
Similar taxa
Althenia is most likely to be confused with Zannichellia palustris which is a superficially similar indigenous aquatic herb of much the same habitats. Zannichellia differs from Althenia by its much-branched floating habit, in having leaves arranged in false whorls of 3-4, and by the flowers arranged together within the sheathing bracts. Submerged plants of Schoenus maschalinus (Cyperaceae) are also superficially similar, but these are much branched, and will not flower when submerged.
Distribution
Indigenous. Known from North, South and Chatham Islands. Also present in Australia.
Habitat
Aquatic herb of lakes, brackish water, or slow-flowing rivers. Usually found in shallow fresh water habitats not far from the coast.
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.
- 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 | At Risk – Naturally Uncommon | Qualifiers: Sp, DPR, EF, RR, SO
Threats
As the result of field surveys it is clear that Althenia bilocularis is biologically sparse in its distribution. In the northern part of its range it seems to have been especially uncommon and there more than anywhere else is where it has undergone some range contraction. However, that loss is insufficient to justify its listing as Threatened.
Detailed taxonomy
Genus
Family
Synonyms
Lepilaena bilocularis Kirk
Taxonomic notes
Althenia bilocularis was initially placed in the genus Lepilaena, as L. bilocularis by Thomas Kirk who discovered it and described it (Kirk 1896). Later Cockayne (1927) placed Lepilaena bilocularis in Althenia, a decision that was not followed by Moore & Edgar (1970). Subsequently using a combination of molecular and morphological data Ito et al. (2016) confirmed the opinion of Cockayne (1927) and resurrected his combination in Althenia and this is followed here.
Endemic taxon
No
Endemic genus
No
Endemic family
No
Ecology
Flowering
Flowers can be present throughout the year
Fruiting
Fruit can be present throughout the year
Propagation technique
No information available.
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
NVS 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.
ALTBIL
Previous conservation statuses
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.
- 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.
2017 | Threatened – Nationally Vulnerable | Qualifiers: EF, RR, SO, Sp
2012 | Threatened – Nationally Vulnerable | Qualifiers: RR, SO, Sp
2009 | At Risk – Naturally Uncommon | Qualifiers: SO
2004 | Sparse
Regional conservation statuses
Otago: 2025 | Regionally Threatened – Regionally Vulnerable | Qualifiers: DPR, DPS, DPT, NStr, TL
The regional threat classification system leverages off the national assessments in the NZTCS, providing information relevant for the regional context. Otago conservation status information is sourced from the “Conservation Status of Indigenous Vascular Plants in Otago, 2025” Jarvie S et al. (2025) report.
Referencing and citations
References and further reading
Cockayne, L.C. in Speight, R., Wall, A. & Laing, R.M. (ed.) 1927: Ecological botany of the Canterbury Plains. Natural History of Canterbury: 126
Ito, Y.; Tanaka, N.; García-Murillo, P.; Muasya, A.M. 2016: A new delimitation of the Afro-Eurasian plant genus Althenia to include its Australasian relative, Lepilaena (Potamogetonaceae)–evidence from DNA and morphological data. Molecular Phylogenetics and Evolution 98: 261-270.
Kirk, T. 1896: Art. LII: Notes on Certain Veronicas, and descriptions of new species. Transactions and Proceedings of the New Zealand Institute 28: 500.
Moore, L.B.; Edgar, E. 1970: Flora of New Zealand. Vol. II. Government Printer, Wellington.
Attribution
Fact Sheet prepared for NZPCN by P.J. de Lange 14 April 2007: Description adapted from Moore and 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): Althenia bilocularis Fact Sheet (content continuously updated). New Zealand Plant Conservation Network. https://www.nzpcn.org.nz/flora/species/althenia-bilocularis/ (Date website was queried)