Hydatella inconspicua (Cheeseman) Cheeseman, Trithuria inconspicua Cheeseman subsp. inconspicua
Vascular – Native
Herbs - Dicotyledons other than Composites
2n = c.24
Current conservation status
The conservation status of all known New Zealand vascular plant taxa at the rank of species and below were reassessed in 2017 using the New Zealand Threat Classification System (NZTCS). This report includes a statistical summary and brief notes on changes since 2012 and replaces all previous NZTCS lists for vascular plants. Authors: By Peter J. de Lange, Jeremy R. Rolfe, John W. Barkla, Shannel P. Courtney, Paul D. Champion, Leon R. Perrie, Sarah M. Beadel, Kerry A. Ford, Ilse Breitwieser, Ines Schönberger, Rowan Hindmarsh-Walls, Peter B. Heenan and Kate Ladley.
2018 | Threatened – Nationally Critical
Previous conservation statuses
2012 | Threatened – Nationally Endangered | Qualifiers: EF, PD, RR
2009 | Threatened – Nationally Vulnerable | Qualifiers: RR
2004 | Serious Decline
Diminutive, tufted, aquatic herb 15-55 mm tall producing numerous unsheathed fine hair like leaves arranged in fans. Inflorescences inconspicuous, borne on stalks 20–40 mm long. Flowers much reduced, male, flower or bisexual. Male flowers with obvious red stamens. Female flowers much reduced reddish.
Endemic. New Zealand. North Island, Northland, where it is known from western dune lakes from near Awanui to the Pouto Peninsula.
An aquatic of shallow to medium depth (5-7m) freshwater lakes (exact depth range dependant on water quality and light levels). Preferring reasonably stable substrates but has been found growing in fine sand, gravel and organic muds. Apparently intolerant of surrounding taller vegetation. Mature plants are often partially buried in sediment so that only their upper most leaf tips are exposed.
Aquatic perennial herb, tufted 15–55 mm high, from a shortly branching erect rhizome, trichomes present; copious adventitious roots. Apomictic or sexual. 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, 15–55 × 0.25–0.4 mm; lamina linear-filiform, adaxially faintly compressed below, terete above, apex rounded with a hydathode. Reproductive units 1–4 per tuft, (3.5–)4–5(–7) mm long, on glabrous terete scapes 20–40 × 0.3–0.4 mm; involucral bracts 2–4(–7), male reproductive unit bracts 3.5–5.0 mm long, ovate to narrow-ovate, stamens (1–)3–8; anthers 0.8–1.4 mm long, bright red, filaments 1–5 mm long. Bisexual reproductive unit bracts 4–5 mm long; stamens 1–5; carpels 2–10. Female reproductive unit bracts 2.5–5.0mmlong; carpels 8–24, reddish, with 5–13 stigmatic hairs of unequal length, 0.3–1.0 mm long, red becoming hyaline. Fruits 0.4–0.56 × 0.2–0.4 mm, ellipsoid to ovoid, deciduous from persistent stalks, pericarp thin and membraneous, smooth, indehiscent. Seed faintly reticulate, yellowish-brown to reddish-brown with a darker apical cap (formed by an operculum).
Trithuria inconspicua is most likely to be confused with some of the spike rushes (Eleocharis spp.) and species of Centrolepis. From these Trithuria differs by its submerged flowering habit, with the male and female flowers usually separate; by the male flowers which have much longer filaments and 2-celled anthers; and by the female flowers which have septate styles that are septate. Vegetative material of Trithuria differs from Centrolepis in that the leaves are not sheathed. Trithuria could be confused with sterile plants of Eleocharis pusilla, however, E. pusilla has uniformly bright green leaves arising from a creeping rhizome. Trithuria brevistyla differs from T. inconspicua by the possession of shortened stigmatic hairs that form a knobbly capitate head; by the void to globose (rather than ellipsoid to ovoid), and by the scapes which do not elongate at maturity
October - December
December - February
Difficult. Should not be removed from the wild.
Seriously threatened in Northland due to the recent spread of the introduced bladderwort Utricularia gibba, and also by the continuing spread of oxygen weeds into these important lakes. Indeed, as of 2004, it has been confirmed as extinct in two more Far North dune lakes.
Fact Sheet by P.J. de Lange (6 January 2004). Fact sheet updated by P.J. de Lange (4 February 2019). Description based on Smissen et al. (2019).
References and further reading
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.
Please cite as: de Lange, P.J. (Year at time of access): Trithuria inconspicua Fact Sheet (content continuously updated). New Zealand Plant Conservation Network. https://www.nzpcn.org.nz/flora/species/trithuria-inconspicua/ (Date website was queried)