Box grass or Knottybutt grass

SCIENTIFIC NAME: Paspalidium constrictum

CATEGORY: C4 perennial


  • A tufted, erect to spreading, warm  season perennial to 60cm tall and with hairy, thickened, knotted stem bases
  • Leaves dull-green to blue-green with  a prominent midrib.  Stems mostly covered  in dense short hairs.  Nodes covered with  soft fine hairs, with a few long hairs
  • Seedhead is a narrow primary axis of  racemes to 35cm long, with the branches pressed against the main axis.  Each branch ends in a short bristle
  • Spikelets have a distinct  constriction along their length
  • Flowers throughout year, but major  flowering is in summer and autumn following rain


  • Widespread on lighter soils (sandy  loam to clay loam); rarely on clays
  • More common on fertile soils where  moisture is high
  • Usually found under tree canopies  and where it is protected from grazing around fallen timber
  • Very drought tolerant and slightly  frost tolerant


  • High grazing value
  • Digestibility  ranges from 35-56% - from one trial only at Cobar
  • Crude protein  11-15.5%


  • Usually only a minor component of  pastures
  • Dry matter yields are low, but it is  highly palatable and regarded as useful forage even after it has hayed off
  • On poor soils it forms a slender  wiry plant, but forms a dense leafy tussock on moister, more fertile sites
  • The bulk of growth is produced in  summer and autumn, but it will produce a green pick throughout the year in all  but the driest times
  • Persists best under rotational  grazing.  It rapidly regenerates when  stock are excluded after heavy grazing, as its buds are below ground level and  protected from damage


  • Slender panic (Paspalidium gracile) is common and very difficult to distinguish;  nodes are usually hairless or covered with minute soft hairs and the seedheads  extend well beyond the leaves
  • The spikelets of warrego summer grass  (Paspalidium jubiflorum) and bent summer grass (Paspalidium  aversum) don’t have constrictions their length.  The latter species has weak and easily  compressed stems that often root at the lower nodes
Box grass

(Plant: L McWhirter)

Further information

See also 'Grassed up' - Box grass.