Gahnia filum, commonly known as Chaffy Saw-sedge, is a tussock-forming perennial herb endemic to coastal heathlands, wetlands, and open forests of southeastern Australia, including New South Wales, Victoria, Tasmania, and South Australia. It typically grows to a height of 24-43 inches (60-110 cm) and is characterized by its long, narrow leaves with serrated edges that can cut skin, hence the name "saw-sedge." The plant produces brownish flower spikes during the summer, which are not particularly showy but are ecologically significant. The dense tussocks provide shelter for various fauna, including the caterpillar of the Yellow Sedge-skipper butterfly, which uses the plant as a daytime refuge.

Chaffy Saw-sedge is valued for its ability to thrive in poor, sandy soils and its tolerance of salt spray, making it suitable for coastal revegetation projects and habitat restoration, particularly at sites like Aldinga Washpool in South Australia. It is also used in ornamental plantings for its textural foliage and as a low-maintenance option in native gardens. Gahnia filum prefers full sun to part shade and can tolerate a range of soil types, provided they are well-drained. While generally pest-free, it can be susceptible to root rot in overly wet conditions. This species is not known for being invasive and does not typically present problems when grown within its native range.CC BY-SA 4.0