gahnia radula seed headGahnia belongs to the Cyperaceae family of monocotyledonous, flowering plants known as sedges. It is native to Australia, New Guinea, China, New Zealand and some islands in the Pacific.

This genus has 40 species, of which 22 are native to Australia. The most notable members are Gahnia aspera and Gahnia sieberiana. [1]

Gahnia aspera was originally described in 1810 by Robert Brown and classified in its current genus in 1825. It is a perennial plant that forms tussocks which are small areas of thick growing grass. Because of its sharp leaf edges, Gahnia aspera is also known as saw-sedge. It is widespread in the rainforests and woodlands of Queensland, New South Wales, New Guinea and Malaysia. The horticultural appeal of Gahnia comes from its distinguished dark and spiked flowers which after flowering produce shiny nuts in red or brownish color. [2]

Even though it’s rather easy to grow, the difficulties in seed propagation make Gahnia aspera unpopular garden plant. When planted in gardens, in moist soil and semi-shade position, it can grow up to 80 cm tall, and spread across 1,5 meters.  Gahnia is host of butterflies that feed on the leaves and offers shelter for birds. The seeds of Gahnia aspera were pounded and used for flour production by Aboriginal Australians. Some parts of the plant like the leaf base and seeds are edible and used as medicine. It is of great importance to be well informed of the preparation process before consuming and using this plant. [3]

gahnia sieberianaGahnia sieberiana known as “Red-Fruit Saw Sedge” it’s the most commonly seen species of this genus. It grows as a very large tussock up to 2 meters in diameter, in full sun or part shade in any free draining soil. Flowers in summer and autumn, and produces black flowers in long pannicles followed by red seeds 4 mm long. Once established, it’s fast growing, hardy, tolerant to frost and requires low maintenance. Gahnia sieberiana makes sterling floral decoration when handled with caution. It is recommended to be planted far from walkways because of its sharp leaves that can cause painful tingling.

Propagation is done by division of clumps. From all Gahnia species, this one is by far the easiest for propagation. Recent studies show that seeds from Gahnia sieberiana can be germinated with application of smoked water and heat followed by incubation. [4]

Gahnia triffida is endemic to southern Australia. It has rigid stem and leaves over 1 meter long. It is often found adjacent to swamps and creeks, in moist soil, clay or sand.

Gahnia radula is another perennial specie native to southeastern Australia found in woodlands and eucalyptus forests. Serves as a food plant for caterpillars and it’s used for erosion soil control. Gahnia radula is a competitive plant that has value in conservation of biodiversity in Victoria.

In 1998 a new Gahnia plant was discovered on Kangaroo Island, South Australia by Bev Overton. The specie was named Gahnia halmaturina and it is closely related to Gahnia hystrix also endemic to Kangaroo Island. [5]