Trithuria brevistyla
Biostatus
Native – Endemic taxon
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 | Threatened – Nationally Vulnerable | Qualifiers: DPT, RR
Category
Vascular
Structural class
Herbs - Dicotyledons other than Composites
Simplified description
Diminutive, tufted, aquatic herb 10-40 mm tall producing numerous unsheathed fine hair like leaves arranged in fans. Inflorescences inconspicuous, borne on stalks 1–6 mm long. Flowers much reduced. Female only.
Flower colours
Red/Pink, White
Detailed description
Aquatic perennial herb, tufted 10–40 mm high, from a shortly branching erect rhizome, trichomes present; copious adventitious roots. Apomictic plants female only. Plants in populations often female only, or plants co-sexual with unisexual or bisexual reproductive units. Leaf-bases weakly dilated (not sheathing), hyaline, toothed auricles present or absent; leaves spreading, glabrous, 8–37 × 0.4–0.6 mm; lamina linear-filiform, adaxially faintly compressed below, terete above, apex rounded with a hydathode. Reproductive units 1–5 per tuft, (3.5–)4–5(–7) mm long, on glabrous terete scapes 1–6 × 0.3–0.4 mm; involucral bracts 2–4(–7), ovate to broad-ovate or narrow-ovate, Female reproductive unit bracts 1.6–4.0 mm long; carpels 9–25, white–pinkish, with stigmatic hairs reduced to a knobbly capitate head (
Similar taxa
Trithuria brevistyla differs from T. inconspicua in the shortened stigmatic hairs forming a knobbly capitate head, the fruit being ovoid to globose (rather than ellipsoid to ovoid), and scapes not elongating with maturity.
Distribution
Endemic. New Zealand. South Island reported from Southland at Lakes Poteriteri, Hauroko, Manapouri, Te Anau and South Mavora Lake and from Lake Sylvan, Otago
Habitat
Shallows of lakes (rarely exposed above the water in a dry season), between 35 and 600 m a.s.l. Growing in sand, silt and gravel, sometimes almost completely buried in muddy silt. Often part of the aquatic-turf community, particularly with short-growing shallow water-species in glacial lakes to a depth of ~0.3–2 m.
Threats
Trithuria brevistyla was listed by de Lange et al. (2018), under the tag-name Trithuria aff. inconspicua (CHR 502359; South Island), as Threatened – Nationally Vulnerable (with qualifiers data-poor, partial decline). Smissen et al. (2019) suggested that this assessment be elevated to Threatened-Nationally Endangered citing as reasons the low area of occupancy estimated by them at 10 ha and their projected decline of 10–50%. However, the New Zealand vascular plant assessment panel maitained the status of Threatened – Nationally Vulnerable in the 2023 assessment without comment on the recommendation of Smissen et al.
Detailed taxonomy
Genus
Family
Synonyms
Trithuria inconspicua subsp. brevistyla K.A.Ford
Endemic taxon
Yes
Endemic genus
No
Endemic family
No
Ecology
Flowering
January - February
Fruiting
March - May
Propagation technique
Difficult - should not be removed from the wild.
Other information
Previous 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.
2017 | Threatened – Nationally Vulnerable | Qualifiers: DP, PD
Regional conservation statuses
Otago: 2025 | Regionally Threatened – Regionally Critical | Qualifiers: DPR, DPS, DPT, NR, NS, NStr, RR
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
de Lange, P.J.; Rolfe, J.R.; Barkla, J.W.; Courtney, S.P.; Champion, P.D.; Perrie, L.R.; Beadel, S.M.; Ford, K.A.; Breitwieser, I.; Schönberger, I.; Hindmarsh-Walls, R.; Heenan, P.B.; Ladley, K. 2018: Conservation Status of New Zealand Indigenous Vascular Plants, 2017. New Zealand Threat Classification Series 22. Department of Conservation, Wellington. 82pp.
de Lange, P.J.; Mosyakin, S.L. 2019: Trithuria brevistyla (Hydatellaceae), a new combination for the New Zealand endemic species from the South Island. Ukrainian Botanical Journal 76 (2): https://doi.org/10.15407/ukrbotj76.02.095
Smissen, R.D.; Ford, K.A.; Champion, P.D.; Heenan, P.B. 2019: Genetic variation in Trithuria inconspicua and T. filamentosa (Hydatellaceae): a new subspecies and a hypothesis of apomixis
arising within a predominantly selfing lineage. Australian Systematic Botany 32: 1–11.
Townsend, A.J.; de Lange, P.J.; Duffy, C.A.J.; Miskelly, C.M.; Molloy, J.; Norton, D.A. 2008: New Zealand Threat Classification System manula. Department of Conservation, Wellington. 35pp.
Attribution
Fact sheet prepared by P.J. de Lange (4 February 2019). Description based on Smissen et al. (2019).
NZPCN Fact Sheet citation
Please cite as: de Lange, P.J. (Year at time of access): Trithuria brevistyla Fact Sheet (content continuously updated). New Zealand Plant Conservation Network. https://www.nzpcn.org.nz/flora/species/trithuria-brevistyla/ (Date website was queried)