Common name
Porcupine Grass

Derivation
Triodia R.Br., Prodr. 182 (1810); from the Greek treis (three) and odous (tooth), referring to the 3-toothed or 3-lobed lemmas.

irritans- from the Latin irrito (irritate). Leaf-blades rigid, pungent.

Published in
Prodr. 182 (1810).

Habit
Perennial, densely tufted. Culms 30–100 cm tall. Mid-culm internodes terete. Leaves distichous. Leaf-sheaths longer than adjacent culm internode, without exudate, indistinctly nerved. Ligule a fringe of hairs. Collar glabrous. Leaf-blade base with a false petiole. Leaf-blades straight, aciculate, conduplicate, 5–25 cm long, 0.5–2 mm wide, coriaceous, rigid, resinous. Leaf-blade apex pungent.

Inflorescence
Inflorescence compound, a panicle, exserted or embraced at base by subtending leaf. Panicle contracted, linear or elliptic or oblong, 5–12(–19) cm long, 1.5–4 cm wide. Primary panicle branches appressed, simple.

Spikelets
Spikelets solitary. Pedicels filiform, 5–15 mm long. Fertile spikelets many flowered, comprising 5–10 fertile florets, with diminished florets at the apex, cuneate, laterally compressed or terete, 11–30 mm long, breaking up at maturity. Spikelets disarticulating below each fertile floret. Spikelet callus bearded, base obtuse. Rhachilla internodes pubescent. Floret callus pubescent.

Glumes
Glumes persistent, similar, thinner than fertile lemma, gaping. Lower glume lanceolate, 9–26 mm long, equalling upper glume, scarious or cartilaginous, 1-keeled, 3–5(–7)-nerved. Lower glume surface glabrous. Lower glume apex entire or lobed, 1–2-fid, acute or acuminate, muticous or mucronate. Lower glume awn 3 mm long. Upper glume lanceolate, 9–26 mm long, 150–170% of length of adjacent fertile lemma, scarious or cartilaginous, 1-keeled, 3–5(–7)-nerved. Upper glume surface glabrous. Upper glume apex entire or lobed, 1–2-fid, acute, muticous or mucronate. Upper glume awn 3 mm long.

Florets
Fertile lemma oblong, 6–12 mm long, scarious or cartilaginous or coriaceous, keeled above, 3(–9)-nerved. Lemma midnerve ciliate. Lemma lateral nerves with distinct primaries but obscure intermediates. Lemma surface scaberulous, pubescent or hirsute. Lemma apex dentate or lobed, 2-fid, with lobes 0.9–1.8 mm long, obtuse or acute or acuminate, mucronate, 1-awned. Median (principal) awn from a sinus, straight, 0.5–6 mm long overall. Palea keels wingless, ciliolate, adorned above. Palea surface glabrous or hirsute. Apical sterile florets resembling fertile though underdeveloped. Lodicules 2, fleshy. Anthers 3, 3–4 mm long.

Continental Distribution:
Australasia.

Australian Distribution:
Western Australia, Northern Territory, South Australia.

Western Australia: Roe, Coolgardie. Northern Territory: Central Australia South. South Australia: North-western, Lake Eyre, Nullabor, Gairdner-Torrens Basin, Flinders Ranges, Eastern, Eyre Peninsula, Southern Lofty.

Classification. (GPWG 2001):
Chloridoideae: Triodieae

Notes
Native, widespread in the southern and central arid regions of Australia. Chiefly in skeletal or shallow, stony or rocky soils on quartzite and granite hills and ranges, often in creeks, rock crevices, gullies and valleys; also limestone soils, saline flats, coastal dunes above a high cliff, sandplains, flats in red sandy loam; flowers all seasons.