Gymnoschoenus sphaerocephalus, commonly known as button grass, is a species of tussock-forming grass from southeastern Australia. It forms part of a unique habitat in Tasmania.

It was originally described as Chaetospora sphaerocephala by Scottish botanist Robert Brown

Robert Brown (botanist)

Robert Brown was a Scottish botanist and palaeobotanist who made important contributions to botany largely through his pioneering use of the microscope...

 in his 1810 work Prodromus Florae Novae Hollandiae et Insulae Van Diemen

Prodromus Florae Novae Hollandiae et Insulae Van Diemen

Prodromus Florae Novae Hollandiae et Insulae Van Diemen is an 1810 flora of Australia by botanist Robert Brown. Often referred to as Prodromus Flora Novae Hollandiae, or by its standard botanical abbreviation Prodr. Fl. Nov. Holland., it was the first attempt at a survey of the Australian flora...

, before being given its current binomial name in 1858 by Joseph Dalton Hooker

Joseph Dalton Hooker

Sir Joseph Dalton Hooker OM, GCSI, CB, MD, FRS was one of the greatest British botanists and explorers of the 19th century. Hooker was a founder of geographical botany, and Charles Darwin's closest friend...

.

Gymnoschoenus sphaerocephalus is a perennial grass species which forms a clump or tussock. The leaf blades reach 50 cm (20 in) in length, and 0.1–0.25 cm in width. The round flowerheads arise out of the tussock, on culms which are up to a metre (3 ft) high. They are around 1.5–2 cm (0.6-0.8 in) in diameter and made up of flattened spikelets 0.5 cm (0.2 in) long. Its root system is a mass of fleshy carbohydrate

Carbohydrate

A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...

-rich rhizome

Rhizome

In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...

s, which are edible.
In New South Wales it is found from Gibraltar Range

Gibraltar Range National Park

Gibraltar Range is a national park in north-eastern New South Wales, Australia, 79 km north-east of Glen Innes and 493 km north of Sydney...

 (and Myall Lakes

Myall Lakes

The Myall Lakes are a series of fresh water lakes on the mid-north coast of New South Wales, Australia in Great Lakes Council. The lakes are adjacent to the coast about north of Sydney....

 on the coast) south to Robertson

Robertson, New South Wales

Robertson is a small town in the Southern Highlands of New South Wales, Australia, in Wingecarribee Shire. The town is located on the edge of an elevated plateau about 35 km from the coast. At the 2006 census, Robertson had a population of 1,206 people.Robertson is known for its high annual...

. It is much more abundant and widespread in Tasmania, where it is common in the western part of the state.

Gymnoschoenus sphaerocephalus grows in damp nutrient-poor soils, and in Tasmania forms a low grassland or moor in which it is the dominant shrub. Associated primitive plants include club mosses such as Lycopodium laterale, and Selaginella uliginosa

Selaginella uliginosa

Selaginella uliginosa is a small perennial plant found in Australia. An ancient and primitive plant, usually under 10 centimetres tall, it is often seen in sunny moist areas. The specific epithet uliginosa is from Latin, referring to the plant's preference to grow in swampy locations....

and the ferns Gleichenia dicarpa

Gleichenia dicarpa

Gleichenia dicarpa is a small fern growing in Australia and New Zealand. Referred to as one of the Coral Ferns. Or more formally listed as the Pouched Coral Fern, Spider Fern, Swamp Umbrella Fern or Tangle Fern....

and G. alpina. despite the wet climate, buttongrass is relatively flammable and the ecological community is adapted to regular burning. The leaves of Gymnoschoenus sphaerocephalus have the lowest recorded phosphorus

Phosphorus

Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...

 content of any plant species. The soil it grows in is a peat which is acidic, with a pH

PH

In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

 of 3.5 to 4.5.

Button grass may form a symbiotic relationship with a species of burrowing crayfish Parastacoides tasmanicus, which aerates the soil with its burrows and in turn feeds on the rhizomes.

It is also a food item of the critically endangered Orange-bellied Parrot

Orange-bellied Parrot

The Orange-bellied Parrot is a small broad-tailed parrot endemic to southern Australia, and one of only two species of parrot which migrate. The adult male is distinguished by its bright grass-green upperparts, yellow underparts and orange belly patch. The adult female and juvenile are duller...

, which breeds in buttongrass moorlands of southwestern Tasmania over the summer.