The saw-sedges (Gahnia sp.) are well known to the bush walker and children for the vicious cuts they leave on exposed legs and arms. In particular the large cutting grass Gahnia grandis has proven a nightmare to many children endeavouring to bush bash their way through thick scrub, which contains many large clumps, interwoven into a dense understorey. However, let me give you something else to think about, when diving into your first aid kit for a bandaid to stem the flow of blood oozing from your finger after your latest encounter with a saw sedge. The saw-sedges have a fascinating set of attributes, which this article will reveal. Hopefully this may help redirect your painful thoughts next time you are doing a skin patch up job.
Firstly the saw-sedges belong to the Cyperaceae family and are hardier representatives than most other members of the family. The papyrus sedge, biblically referred to for its use in Egyptian papermaking, and the bulbous rooted water chestnut, used as a tasty and crunchy additive in Chinese cooking, are well known members of this family.
The best-known member of the saw-sedge genus is the large cutting grass Gahnia grandis. Typical of the saw-sedges, they have thin weeping leaves with distinctive sharp saw-like leaf edges, formed from tiny granules of silica incorporated into the leaf surface. Many an unsuspecting child's limbs have been deeply gashed as a consequence of these sharp leaves brushing across their unprotected skin. Fingers often suffer deep wounds when trekkers grab its foliage.
Interestingly, cutting grass relies on birds such as the currawong for germinating its seed, more correctly referred to as small nuts. The currawong eats and regurgitates the red flesh covered seed, with the aid of a gullet full of water. This helps purge out a reddish bolus of partially digested fruits. The currawong's stomach acid etches these seeds weakening their tough seed coats to allow ease of germination. This is an intriguing example of how co-evolution between native plants and wildlife ensures mutual benefits for both.
As understorey in wet sclerophyll forests, these large tussocks are notorious habitat for the white-lipped and black tiger snakes. These snakes flattened their bodies when disturbed by children, while basking between tussocks or preying on skinks, frogs or small mammals.
For the gardeners, cutting grass Gahnia grandis along with the red fruit saw-sedge Gahnia sieberiana can take pride of place as feature plants. Fringed by their 2 metre strap-like leaves, their long plume-like flowering heads and bright red fruits, they present wonderful landscaping potential.
Although common in the drier woodlands, the thatch saw-sedge (Gahnia radula) with its characteristic thin leaves that droop markedly at their tips are not noticed unless walkers' bare legs begin to feel as though they are being sandpapered.
The rapidly browning landscapes of summer are punctuated with drifts of dark brown flowers, dashed with the cream colour of their thread-like anthers. These supply pollen to the delicate chaostola skipper butterfly whose larvae (caterpillar) occupy cylindrical shelters constructed from 2 or 3 leaves drawn together and bound with silk. The mottled brown and yellow butterflies remain in close flying distance to the flowers during the October to December period.
Both the flame skipper and donnysa skipper butterfly also rely on either the thatched saw-sedge or large cutting grass for their survival. The male donnysa skipper is very territorial, engaging other males in spiralling flights as it endeavours to defend its patch and attract females. Once mated, tiny yellowish green eggs are laid under the leaves, hatching into caterpillars with distinctive dark streaks along their green bodies. This camouflage only partially protects them from the native birds, which successfully scavenge large numbers to feed their young nestlings. However, they are rarely missed by the greater and lesser long-eared bats, which feed slowly close to the ground and, at times, amongst these tussocks.
By late summer, the thatch saw -sedge flower heads ripen to form hundreds of small nuts. Once harvested, these nuts can be pounded and ground into flour for making flat breads. The young leaf bases can provide a tasty pea-like snack when harvested from plants grown with sufficient soil moisture. The waist high leaves can be woven into traditional items such as baskets and dillies. Traditionally they are split, left to dry for a few days and stored for later use. To render them pliable for weaving they require dampening for a day.
Frequently, families on strolls who enjoy either coastal or estuarine tracks encounter wide expanses of the chaffy saw-sedge (Gahnia filum) often in association with coastal tussock and spear grasses. This sedge land occupies the margins of brackish estuarine marshes and saline water bodies. Common in the Lauderdale and Pittwater inter-tidal wetland flats, these sedges form part of the crucial habitat for many of our migratory birds such as the pied oystercatcher and hooded plover.
Their roots also act as one of the hosts for the microbes that filter the detritus from the nutrient laden tides. Hence it performs a fundamental role in the food web for these wetland communities. Children would also tune into the banjo-like "bong….bong…" of the eastern banjo frog and/or the lamb-like quavering bleat "baa-aa-aaaa" of the Tasmanian froglet, which both survive happily under the dense canopy of these insect rich sedge lands.
Along with the coast saw-sedge (Gahnia trifida) they host the erratic flying chrysotricha skipper butterfly. Their larvae have the unusual habit of twisting adjacent leaves together in a spiral fashion to form their characteristic shelter.
Only the most observant walker would discover amongst the dry woodland ground layer the insignificant Gahnia rodwayi. It is uncommon, small and compact saw-sedge growing in dry sclerophyll understorey on dolerite soils. Since it is listed as a rare plant, increasing its rapidly diminishing populations by adding it to your native garden should be contemplated. The 'do it yourself' gardener may even consider gathering the easily collectable seed. Although like Gahnia radula it can be slow to germinate, the commitment to successfully growing it's seedlings is a worthy challenge.
With the above information budding gardeners may feel inspired enough to use the saw sedges as part of a drought tolerant garden patch. This requires establishing a well-mulched framework of hardy native grasses, sedges and rushes including the saw sedges. The saw sedges, like our native grasses and other sedges such as the sagg and native flax and native iris are adapted to survive drought periods without supplementary watering.
Within the inter-tussock spaces, which they form, delicate herbaceous natives can be planted such as everlasting daisies, billy buttons, chocolate and leek lilies and native cranberries. These drought adapted herbs, with their lush green leaves and colourful spring flowers will generally die back to their underground rootstocks by the onset of our dry summer and autumn. However they reappear in all their splendour by early spring.
Finally, next time you inadvertently walk into the sharp realities of saw sedges, rather than cursing their presence, reflect on of the many natural values they possess and nature's services they perform.
Phil Watson
