Trithuria inconspicua
A tiny New Zealand aquatic herb at the center of angiosperm evolution debate.
Trithuria inconspicua is a small aquatic herb in the Hydatellaceae family, found only in New Zealand. It grows 15–55 mm tall, with a rhizome up to 2 cm long and 3 mm wide, adventitious roots, and glabrous, linear-filiform leaves of the same length and 0.25–0.4 mm wide. The plant can be monoicous or partly exclusively female, with bisexual or unisexual reproductive units. Female plants are more common, but male and bisexual individuals occur. Male flowers have bright red filaments 10 mm long, while female flowers are yellow-brown with 5–10 styles clustered at the tip. Its chloroplast genome is 165,389 base pairs long.
The species was described by Thomas Frederick Cheeseman in 1906, based on a lectotype collected by H. Carse in Lake Ngatu, New Zealand, on 1 January 1902. It belongs to the section *Hydatella*. Two subspecies are recognized: the autonymous *Trithuria inconspicua* subsp. *inconspicua*, found in coastal dune lakes in the north of North Island, and *Trithuria inconspicua* subsp. *brevistyla*, described in 2019 by K.A. Ford, found in glacial lakes in the south of South Island. The specific epithet *inconspicua* means inconspicuous, or not easily visible.
Originally thought to be a monocot based on a single plastid gene (*rbcL*), later studies using multiple genetic loci and re-evaluated morphology place *T. inconspicua* as a sister group to water lilies (Nymphaeales). This means only one flowering plant lineage is considered older: the woody New Caledonian shrub *Amborella trichopoda*. However, a 2013 study by Goremykin et al. challenged this, finding *T. inconspicua* as the oldest angiosperm when highly variable sites were removed. Drew et al. (2014) criticized this, arguing the result was an artifact of the filtering method. If *T. inconspicua* is basal, it suggests the first angiosperms were soft-bodied aquatic plants rather than woody terrestrial ones like *Amborella*. These competing ideas are nicknamed "wet and wild" and "dark and disturbed."
The species is seriously threatened by competition from introduced bladderwort (*Utricularia gibba*) and other freshwater weeds. It grows in coastal dune lakes and glacial lakes, in shallow to 5–7 m deep waters, on mud, sand, and gravel substrates, often partly buried. In 2024, it was chosen as New Zealand's Favourite Plant.
Quick Facts
- Genus
- Trithuria
- Parent
- Trithuria sect. Hydatella
- Species
- inconspicua
Facts from the source article.
Lore & Background
Trithuria inconspicua was published by Thomas Frederick Cheeseman in 1906, with a lectotype specimen collected by H. Carse in Lake Ngatu, New Zealand on 1 January 1902. It is placed in Trithuria sect. Hydatella and divided into two subspecies: the autonymous Trithuria inconspicua subsp. inconspicua, found in coastal dune lakes in the North of North Island, New Zealand, and Trithuria inconspicua subsp. brevistyla K.A.Ford described in 2019, found in glacial lakes in the South of South Island, New Zealand. The specific epithet inconspicua means inconspicuous, not easily visible. The plant is a small, 15–55 mm tall, aquatic, perennial, rhizomatous herb with adventitious roots and glabrous, linear-filiform leaves. It can be monoicous or in part exclusively female, with bisexual or unisexual reproductive units. Female plants are more frequent, with yellow-brown flowers containing 5-10 styles bunched at the apex, while male flowers have bright red 10 mm long filaments. It occurs in coastal dune lakes and glacial lakes in shallow to 5–7 m deep waters, growing in mud, sand, and gravel substrates, often partly buried.
Reader's Guide
Trithuria inconspicua holds significance primarily due to its contested role in angiosperm evolution. Originally believed to be a monocot based on a single plastid gene (rbcL), more recent multi-locus genetic studies and morphological re-evaluation place it as a sister group to water lilies (Nymphaeales), making it older than all flowering plants except Amborella trichopoda. However, a 2013 study by Goremykin et al., which removed highly variable sites from the dataset, consistently identified T. inconspicua as the oldest angiosperm lineage. This proposal was criticized by Drew et al. (2014), who argued the basal placement was an artifact of the variable site filtering method. If T. inconspicua were the oldest, it would suggest the first angiosperms were soft-bodied aquatic plants rather than woody terrestrial ones—theories nicknamed 'wet and wild' versus 'dark and disturbed'. The species is seriously threatened by competition from the introduced bladderwort Utricularia gibba and other freshwater weeds. It was chosen as New Zealand's Favourite Plant 2024.
Did You Know?
- Trithuria inconspicua is only found in New Zealand.
- Its chloroplast genome is 165389 bp long.
- The species is seriously threatened by the introduced bladderwort Utricularia gibba.
Frequently Asked Questions
What is Trithuria inconspicua?
It is a diminutive freshwater herb found only in New Zealand, classified in the Hydatellaceae family. The whole plant rarely exceeds 55 millimeters in height, making it one of the smallest known aquatic angiosperms.
What does Trithuria inconspicua look like in detail?
Its glabrous, thread-like leaves measure 15–55 mm long but are only 0.25–0.4 mm wide, and the plant is anchored by a short rhizome up to 2 cm long and 3 mm wide. Male flowers display vivid red filaments about 10 mm in length, while female blooms are yellow-brown with a tight cluster of 5–10 styles at the tip.
Can I keep Trithuria inconspicua in a planted aquarium?
Because it is endemic to New Zealand, extremely small, and not commercially propagated, it is virtually unavailable through the standard hobby-plant trade. Enthusiasts who encounter it do so mainly through botanical research collections rather than retail aquarium suppliers.
Why is Trithuria inconspicua important to angiosperm evolution research?
Its reproductive architecture and a 165,389-base-pair chloroplast genome supply critical data for reconstructing the deep branching of flowering-plant phylogeny. Researchers point to its unusual combination of monoecious and gynodioecious strategies as a window into early angiosperm diversity.
How does Trithuria inconspicua reproduce, and is it mostly male or female?
The species produces both bisexual and unisexual units, but female individuals are the most common form in the wild, with male and fully bisexual plants occurring less frequently. This skewed, mixed reproductive system makes simple sex-ratio predictions difficult for anyone studying a population.
More in Aquarium and Aquatic Plants, Part 3 1-24
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