Download Gymnoschoenus sphaerocephalus

Gymnoschoenus sphaerocephalus
FAMILY: Cyperaceae
BOTANICAL NAME: Gymnoschoenus sphaerocephalus
COMMON NAME: buttongrass
CONSERVATION SIGNIFICANCE:
None recorded
Micah Visiou
Description
Buttongrass is a perennial sedge that forms large, densely-tufted, coarse tussocks from
which arise long stalks (culms) bearing spherical flower-heads, which form the
characteristic “buttons”.
The greyish, yellow-brown leaf sheaths are up to 20 cm long, more or less shiny,
finely-grooved and open, with long, brown hairs on the margin of the sheath apex and
on the apex of the small papery structure (ligule) located at the leaf sheath–leaf blade
junction. The leaf blade is smooth, hard, long (up to 60 cm) and narrow (1–2.5 mm
wide). In cross-section, the leaf blade is flat on one side and rounded and curved
outward (convex) on the other side, and is sometimes spirally twisted.
The flower-head stalks (culms) are often 1 m or more in length, 1–2.5 mm in
diameter, cylindrical or slightly flattened, finely-grooved but smooth, hairless and
rigid with no nodes, bearing a globe-shaped flower-head at the top. The flower-head is
dense, usually 1.5–2 cm in diameter, and cupped underneath by a whorl of leaf-like
structures (involucral bracts) that are more or less circular and enfold the flower-head
when in bud. These bracts have either sharp or leaf-like tips, are flat, up to 5 mm long
and hairy at the base. There are also smaller bracts within the flower head, which are
notched at the tip and pointy, with papery margins that rapidly become torn. The
flower-head is composed of smaller units (spikelets) that are numerous, flattened and
5-6 mm long. Each spikelet has 6–7 yellow-brown, glistening leaf-like structures
(glumes). The lower glumes are empty, papery and dark brown. The upper glumes are
longer and more or less hardened, and enfold the flower units (florets). Each spikelet
holds two florets. The upper floret is bisexual and the lower one is male. The male
floret’s stamens have flattened filaments and 4 mm long anthers. The bisexual floret
has a 5 mm long style and short stiff bristles attached below the ovary (hypogynous),
which are either 2.5 mm or 4 mm long, or absent. The fruit (nut) is 4 mm long
(including the reverse pyramid-shaped stalk). The fruit is reverse egg-shaped, with a
persistent style base, the outermost layer of which is loose, thin and easily removed.
When the fruit falls, it remains enfolded in the upper glumes.
Flora of Tasmania
Gymnoschoenus sphaerocephalus
Confusing species
None in Tasmania.
Distribution and Habitat
Distribution of Gymnoschoenus sphaerocephalus
in Tasmania according 2004 data
Buttongrass moorland distribution in
Tasmania . TASVEG 2004.
In Australia, buttongrass occurs in South Australia, Victoria, New South Wales and
Queensland. In Tasmania, it occurs in the northwest, northeast, east coast, southwest
and central highlands in areas of high rainfall on poor soils.
On slopes where the drainage is better, buttongrass occurs in sedgeland heaths and
other open communities. It develops into a hummock in low closed scrub and sedge
communities. It is most common on peat overlying quartzite gravels, where it forms
extensive areas of moorland from near sea level to an altitude of 900 m, where it is
often the signature species. Buttongrass moorlands are widespread in northwestern,
western and southwestern Tasmania. These moorlands dominate the landscape in the
wetter southwest and western areas but occur only as small isolated pockets in the
drier north and east. The eastern buttongrass moors occur mostly on poorly-drained
flats or depressions with waterlogged soils or seasonally wet mineral soils, mainly
loams and sandy loams.
Ecology
Buttongrass can thrive on very poor sites with low levels of nutrients and impeded
drainage. Buttongrass employs a number of strategies to overcome the limitations of
such sites. In response to low nutrient conditions, this species has evolved
scleromorphic characteristics such as tough, long-lived leaves (culms) with high
contents of oil, lignin and silica, which allow the plants to survive in the anaerobic,
acid soils where the nutrient availability is extremely low. In the cool, wet, acidic
conditions that prevail much of the year in the sites preferred by buttongrass,
decomposition is slow so recycling of nutrients back into the soil is also slow and thus
much of the nutrients are bound up in plant matter. As the long-lived leaves age,
nutrients are probably withdrawn from the leaves and taken up by new rhizomes to
Flora of Tasmania
Gymnoschoenus sphaerocephalus
maintain the nutrient supply to the tussock. After death, the leaves do not decay but
remain attached to plants long afterwards. Over time a large amount of dead plant
material accumulates, which tends to dry quickly after rain. These features make the
plants very flammable and pyrogenic.
Another feature is the white, fleshy (and edible) rhizomes, with the capacity for
considerable carbohydrate storage, which enables the plants to recover after an
adverse event such as fire or drought. These fleshy rhizomes form a dense bundle
close to the surface, penetrating 5–10 cm below the peat. The structure of the rhizome
elevates the tussock above the water table for at least some of the year, maximising
the available oxygen and enabling the plants to cope with impeded drainage and lack
of oxygen in the soil. At some sites, the rhizomes can form large pedestals (up to
50 cm high) and the top of the plants may reach 2 m in height. In some cases,
rhizomes can penetrate the peat to depths of 15–20 cm and are often seen growing
along the tunnels of burrowing crayfish (Parastacoides tasmanicus). In fact,
buttongrass plants tend to be the preferred sites for the crayfish burrows. Evidence
suggests that a symbiotic relationship may exist between the crayfish and buttongrass,
where the crayfish improves aeration of the peat while the plant’s fleshy rhizomes
provide a food source.
Buttongrass is well adapted to fire and can recover vegetatively after fire. However,
the tussocks can be killed by even a moderate fire if the conditions are dry or in areas
where there is little peat cover, as the rhizomes require wet peat to protect them from
heat damage.
Regeneration after fire is quite rapid and buttongrass can produce shoots 10–20 cm
long 3 months after a low intensity spring or autumn fire. Some plants can produce
flower buttons 6 months after a mild autumn fire, which suggests they use the
carbohydrates stored in the rhizomes prior to spring growth. The buttons generally
appear 3–4 years after a mild spring fire, about the same time as new leaves appear.
Flowering occurs during the following season, which for most tussocks is during late
November and early December.
In the absence of fire, the main flush of growth occurs early in spring, with flowering
occurring from spring through to summer and seed produced from December through
to March.
Buttongrass is not an aggressive species and does not rapidly colonise areas. Rather, it
seems to spread slowly in a stepwise manner from the parent plants. It is dispersed
principally by seed rather than by vegetative spread. The seeds seem to require high
light and moisture levels for germination. For example, waterlogged sites with patches
of exposed soil or well-lit disturbed sites, such as those along roadsides and tracks,
appear to be very favourable for germination. Seedlings are more likely to establish
where there has been partial removal of peat and less likely to establish on bare
quartzite, where the rhizomes have difficulty penetrating the rocky surface. Seedling
densities observed are low, especially when compared with that observed in some
shrub species. This observation is consistent with the discovery that the buttons
produce few viable seeds.
It is possible that buttongrass may be spread more widely via dispersal by birds, since
its seed are a source of food for species such as ground parrots. If bird dispersal does
occur it is apparently not a highly successful process, as itinerant seedlings or young
plants of buttongrass are not encountered as widely as are those of Gahnia species
Flora of Tasmania
Gymnoschoenus sphaerocephalus
(sawsedges) and Cenarrhenes nitida (native plum) for example, which are also
dispersed by birds. Ant colonies may help disperse seed short distances, as they have
been observed gathering buttongrass seed.
Buttongrass is resistant to Phytophthora cinnamomi but acts as a host for this disease.
Buttongrass is the signature species of buttongrass moorlands. Globally, this is a
unique vegetation type.
Potential for Cultivation
The cultivation potential of this species is low. Buttongrass tends to produce few
viable seed. The seed is very difficult to germinate, with the best results achieved
when a heat bed is used.
The flower stalks (culms) are currently used in basket making. The flower-heads are
also generating some interest for use in floriculture.
Information Sources
Curtis, W.M. & Morris, D.L. (1994) The Student’s Flora of Tasmania. Part 4B. St.
David’s Park Publishing, Hobart.
Gellie, N.J.H. (1980) Fire Ecology of Buttongrass Moorlands. Bulletin 6. Forestry
Commission, Tasmania.
Jarman, S.J., Kantvilas, G. & Brown, M.J. (1988) Buttongrass Moorland in
Tasmania. Research Report No. 2. Tasmanian Forest Research Council Inc.
Marsden-Smedley, J. (1993) Fuel Characteristics and Fire Behaviour in Tasmanian
Buttongrass Moorlands. A fire and research study conducted by the Protection
Branch, Parks and Wildlife Service, Department of Environment and Land
Management, Hobart, Tasmania.
Marsden-Smedley, J., Catchpole, W.R. & Pyrke, A. (1998) Unbounded Burning in
Tasmanian Buttongrass Moorlands. Unpublished report prepared for the Tasmanian
Fire Research Fund. Parks and Wildlife Service, Forestry Tasmania and Tasmania
Fire Service.
Understorey Network. Tasmanian Native Species Database. www.understoreynetwork.org.au
Walsh, N.G. & Entwisle, T.J. (1994) Flora of Victoria. Vol. 2. Inkata Press,
Melbourne.
Flora of Tasmania