Plants of
South Australia
Machaerina tetragona
Square Twig-sedge,
Square Twig-rush
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Regional Species Conservation Assessments per IBRA subregion.
Least concern
Near threatened
Critically endangered
Data deficient
Coober Pedy
Mount Gambier
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Botanical art

Kath Alcock painting: 1

Prior names

Baumea tetragona

Lepidosperma tetragonum

Cladium tetraquetrum

Cladium tetragonum

Common names

Square Twig-sedge

Square Twig-rush


Machaerina from the Latin 'machaera' meaning a bent dagger or sword, and the feminine diminutive suffix '-ina", referring to the shape of the leaves of some species (formally Baumea named after Antoine Baume (1728 - 1804), a French chemist and inventor). Tetragona from the Greek 'tetra' meaning four and 'gonia' meaning an angle, referring to the square cross section of the stem.

Distribution and status

Found on Kangaroo Island, southern Mount Lofty Ranges and the lower South-east in South Australia, growing in swamps. Also found in Queensland, New South Wales, Victoria and Tasmania. Native. Uncommon in South Australia. Rare in Queensland. Common in the other States.
Herbarium regions: Southern Lofty, Kangaroo Island, South Eastern, Green Adelaide
NRM regions: Adelaide and Mount Lofty Ranges, Kangaroo Island, South East
AVH map: SA distribution map (external link)

Plant description

Perennial sedge with slender stems to 120 cm long and 2 mm wide, prominently 4-angled in the upper part, often compressed or subterete in the lower part. Leaves all basal, acutely 4-angled, much wider and sometimes as long as the stem, the tip very acute; inner leaves often reduced to the sheath with lowest bract reduced to its sheath. Flowers in dense panicles with crowded brown-black spikelets. Flowering between spring and summer. Fruits are dense brown-black heads at the tip of stems. Seeds are pale yellow-brown ovoid nut to 2 mm long and 1 mm wide, with a wrinkled surface. Seed embryo type is capitate.

Seed collection and propagation

Collect seeds between November and March. Collect whole heads that are brown, containing dark hard seeds. Not all heads will contain seeds. Place the heads in a tray and leave to dry for one to two weeks. Then rub the heads with a rubber bung to dislodge the seeds. Use a sieve to separate any unwanted material. Store the seeds with a desiccant such as dried silica beads or dry rice, in an air tight container in a cool and dry place. Not all mature seeds are viable. Seed viability is variable depending on maturity of seeds when collected. This species is generally difficult to germinate, it has morphophysiological dormancy and complex germination requirements.

Seeds stored:
LocationNo. of seeds
(weight grams)
of plants
Collection number
Collection location
% ViabilityStorage
BGA20,500 (15.38 g)7-Dec-2006RJB70682
Southern Lofty
Location: BGA — the seeds are stored at the Adelaide Botanic Gardens, MSB — the seeds are stored at the Millennium Seed Bank, Kew, England.
Number of plants: This is the number of plants from which the seeds were collected.
Collection location: The Herbarium of South Australia's region name.
% Viability: Percentage of filled healthy seeds determined by a cut test or x-ray.