Common name
Knottybutt Grass
Box Grass
Knottybutt Paspalidium

Derivation

Paspalidium Stapf in D.Prain, Fl. Trop. Afr. 9: 15, 582 (1920); from Paspalum (another grass genus) and the Greek -idium, a diminutive but here employed as a name-forming suffix.

constrictum- from the Latin constringo (bind together). Panicle branches held erect.

Published in
Bull. Misc. Inform. 447 (1934).

Common synonyms
Setaria constricta (Domin) R.D.Webster
Panicum constrictum Domin
Panicum flavidum Retz. var. tenuis Benth.
Paspalidium gracile (R.Br.) Hughes var. rugosum Hughes

Habit
Perennial, tufted. Rootstock evident. Cataphylls present. Young shoots extravaginal. Culms erect or decumbent, 10–60 cm tall, 4–7-noded. Mid-culm internodes solid or spongy, pubescent. Mid-culm nodes pubescent. Lateral branches sparsely branched or branched. Leaf-sheaths antrorsely scabrous, glabrous on surface or pilose, with tubercle-based hairs. Leaf-sheaths outer margin glabrous. Ligule a fringed membrane or a fringe of hairs, 1.25 mm long. Leaf-blades 6–15 cm long, 1–4 mm wide. Leaf-blade surface scabrous, glabrous or pilose, with tubercle-based hairs. Leaf-blade margins smooth. Leaf-blade apex attenuate.

Inflorescence
Inflorescence compound, a panicle of racemes. Racemes 5–10, appressed, unilateral, 0.45–3 cm long, 0.15–0.3 mm wide, bearing few fertile spikelets, bearing 5–12 fertile spikelets on each. Central inflorescence axis 6–15 cm long, pubescent, tip filiform. Rhachis angular, 0.4 mm wide, pubescent on surface, scabrous on margins, terminating in a barren bristle-like extension, extension 3–6 mm long. Spikelet packing abaxial, irregular, 2-rowed.

Spikelets
Spikelets solitary. Pedicels 0.25–1.5 mm long, tip discoid. Fertile spikelets 2-flowered, comprising 1 fertile floret, lower floret sterile, upper fertile, without rhachilla extension, elliptic, dorsally compressed, plano-convex, acute, 2.25–3.6 mm long, falling entire. Rhachilla internodes elongated between glumes, elongated below basal sterile floret, and elongated below proximal fertile floret.

Glumes
Glumes thinner than fertile lemma. Lower glume oblate, clasping, gibbous, 1.3–1.9 mm long, 60–66% of length of spikelet, membranous, (3–)5-nerved. Lower glume surface glabrous or puberulous. Lower glume apex acute, muticous. Upper glume orbicular, 2.1–2.9 mm long, 75–90% of length of spikelet, membranous, 7–9-nerved. Upper glume apex obtuse or acute.

Florets
Basal sterile florets 1, without significant palea. Lemma of lower sterile floret similar to upper glume, elliptic, 2.5–3.5 mm long, 100% of length of spikelet, membranous, 5-nerved, sulcate, acute. Fertile lemma elliptic, 2.25–3.5 mm long, indurate, of similar consistency on margins. Lemma surface rugulose or rugose, with distinct germination flap. Lemma margins flat or involute. Lemma apex acute, muticous. Palea reflexed at apex, indurate, 2-keeled. Palea surface rugose. Grain with adherent pericarp.

Continental Distribution:
Australasia.

Australian Distribution:
Western Australia, Northern Territory, South Australia, Queensland, New South Wales, Victoria.

Western Australia: Giles, Helms, Fortescue, Ashburton, Austin, Eucla, Irwin, Drummond. Northern Territory: Darwin & Gulf, Barkly Tableland, Central Australia North, Central Australia South. South Australia: North-western, Lake Eyre, Nullabor, Gairdner-Torrens Basin, Flinders Ranges, Eastern, Eyre Peninsula, Northern Lofty, Murray, Yorke Peninsula, Southern Lofty. Queensland: Cook, Burke, North Kennedy, South Kennedy, Port Curtis, Leichhardt, Burnett, Wide Bay, Darling Downs, Moreton, Gregory North, Mitchell, Warrego, Maranoa. New South Wales: Central Coast, South Coast, Northern Tablelands, North-Western Slopes, Central-Western Slopes, North-Western Plains, South-Western Plains, North Far Western Plains, South Far Western Plains. Victoria: Murray Mallee, Riverina, Midlands, Victorian Volcanic Plain, East Gippsland.

Classification. (GPWG 2001):
Panicoideae: Paniceae

Notes
Native. In semi-arid shrub woodlands, shrub steppe shrublands, acacia shrublands, eucalypt shrublands, arid tussock grasslands, and arid hummock grasslands. Flowers mostly Apr.–Aug.