Triodia stenostachya  Domin 1915

pronounced: try-OH-dee-uh sten-oh-STAK-ee-uh 

(Poaceae —  the grass family)

common names: Porcupine Grass, Spinifex

Triodia triodia stenostachyaspinifex (porcupine grass)triodia stenostachyafloweringis from two Greek words, τρια (tria), three, and οδους (odous), tooth, referring to the divided lemma; stenostachya is from στενος (stenos), narrow, and σταχυς (stachys), an ear of corn, spike.  Although this grass is called ‘spinifex’ all over Australia, it is not a spinifex. The genus Spinifex, somewhat similar in appearance, but with vastly different flowers, is confined to sandy habitats along coastal beaches, while the members of the Triodia genus are found not only on low-nutrient soils of inland sand plains in the arid inland, but also on rocky outcrops along the coast. Hummock grasses in the genus Triodia dominate the vegetation of 20% of Australia, and this grass is plentiful on most of the Magnetic Island headlands. The various members of the genus are notoriously difficult to identify, but I am fairly sure that our local plants are Triodia stenostachya – the other possibility is Triodia scariosa.

Triodia triodia stenostachya fruiting spikesfruiting spikesusually form coarse tussocks, with the green leaves on the outer surface. The inside of the tussock consists of densely matted stems and dead leaves. When the leaves are young, they are flat and relatively soft, but as they are, the edges roll under and the leaf becomes very stiff and pointed. Older specimens can develop into rings. Some species secrete resin from the leaves, and Aboriginal people used the resin as an adhesive, particularly in spear-making. They also collected the seeds and ground them into a flour. Smoke signals were made with spinifex to communicate with families and groups a long distance away, as the plant burns with a readily visible black smoke. The leaves are extremely prickly, hence the ‘porcupine’. Viewed from a distance, Triodia can be attractive, especially when they are in flower, but close encounters will soon change your mind about that, especially if you accidentally step back into one when photographing something else.

They are, in fact, quite useful plants, providing ground cover to slow down soil erosion, and giving refuge to various small bush creatures who scuttle in under the plants. When rings are formed, other plants such as tree seedlings are often found growing in the central space, safe from grazing predators.

The plants grow in dense clumps, with culms 30 – 200 cm long, 1 mm or a little more in diameter. The leaf-blades are curled or flexuous, about 40 cm long, and 0.6-1.3 mm wide. The inflorescence is a compound panicle 20-40 cm long. The spikelets are solitary and consist of at least 2 fertile florets, with diminished florets at the apex. These apical sterile florets resemble the fertile ones, though they are underdeveloped. The glumes are shorter than the spikelets. The flowers have three anthers.

Especially in the arid inland regions, Triodia are very susceptible to fire (often caused by lightning strikes), but regenerate fairly rapidly, either as seedlings arising from a soil seed bank, or from re-sprouts from the bases of the tussocks.

Photographs taken 2005-2010, Hawkings Point & Florence Bay

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