1. Bristles or spines joined to some degree at the base, forming a burr

    Bristles free or almost free to the base, fine and thread‑like



  2. Spines connate for more than 1/3 of distance above base 3
    Spines connate to 1/3 of distance above base 6
  3.   Burr of 1 whorl of united flattened spines surrounded by many smaller finer    bristles 4
      Burr of several whorls of united flattened spines surrounded by many smaller finer bristles 5
  4.  Outer bristles and inner spines ± equal in length *C. brownii (NT WA QLD)
     Outer bristles ± 1/2 length of inner spines *C. echinatus (NSW NT WA QLD)
  5.   Spines slender, usually more than 30 *C. longispinus (NSW VIC NT SA WA QLD)
C. pauciflorus var. longispinus, C. tribuloides auct.
      Spines broader at base, less than 25 *C. spinifex (NSW VIC SA WA QLD)
C. pauciflorus, C. tribuloides auct.
  6.   Spines retrorsely barbed 7
     Spines antrorsely barbed 9
  7.   Spines grooved externally *C. biflorus (NT WA QLD)
C. barbatus
      Spines not grooved externally 8


8.  Burr with one spikelet 3.8-6mm long C. caliculatus (NSW QLD)
C. australis
    Burr with two spikelets 8-9mm long C. robustus (QLD)
9.  Spines not extending beyond burr

* C. setigerus  (NSW NT WA QLD)

Pennisetum setiger

     Spines or a single spine extending beyond burr


10.  Spikelets c. 8 mm long


      Spikelets c. 5 mm long 12
11.  Burr with a single elongated bristle and a few very short basal bristles

C. brevisetosus  (NT WA QLD)

      Burr with many bristles as long as or extending beyond spikelets,  one of them  at least three times longer than the others

C. elymoides (NT WA QLD)

12. Bristles joined together only at base

* C. ciliaris  (NSW NT SA WA QLD)

Pennisetum ciliare

Bristles joined together above base for 1-3 mm

* C. pennisetiformis  (NT SA WA QLD)

Pennisetum pennisetiforme

  13. Inflorescence concealed within uppermost leaf sheath

* C. clandestinus (NSW VIC TAS SA WA QLD)

Pennisetum clandestinum

    Inflorescence exserted from uppermost leaf‑sheath 14
  14.  Rachis angular 15
       Rachis cylindric 18
  15.  Involucral bristles scaberulous; rachis hair

C. basedowii   (NT WA QLD)

Pennisetum basedowii

     Involucral bristles hairy; rachis glabrous or scaberulous 16
  16. Spikelet sessile within involucre

 * C. polystachios  (NT QLD)
Pennisetum polystachyum

     Spikelet pedicelled within involucre 17
  17. Involucre with 1 spikelet

* C. pedicellatus  subsp. unispiculus  (NT WA QLD)

Pennisetum pedicellatum subsp. unispiculatum

     Involucre with 2‑5 spikelets

* C. pedicellatus  subsp. pedicellatus (NT WA )

Pennisetum pedicellatum subsp. pedicellatum

  18.  Annual; grain exserted at maturity from gaping spiklelet  * C. americanus   (NSW NT WA QLD)
Pennisetum glaucum
      Perennial; grain not exserted from spikelet 19
  19. Involucres on a stalk 1-3 mm long 20
      Involucres subsessile 22
  20. Involucre bristles glabrous 

  * C. purpurascens   (NSW VIC QLD)

  Pennisetum alopecuroides. P. compressum   

     Involucre bristles hairy 21
  21. Spikelets 9-10 mm long

* C. longisetus    (NSW VIC TAS SA WA QLD)

Pennisetum villosum

     Spikelets 5-6 mm long

* C. setaceus   (NSW VIC SA WA QLD)

Pennisetum setaceum


22. Slender plant to 60 cm long; inflorescence c. 5 cm long  * C. thunbergii   (QLD)

Pennisetum glabrum, P.thunbergii

     Vigorous plant exceeding 1.5 m; inflorecence 8-30 cm long 23

23. Bristles scabrous, slightly longer than spikelets except for a single longer bristle; culms not  branched

* C. macrourus (NSW VIC TAS SA WA)

Pennisetum macrourum

      Bristles scabrous to hairy, at least 3 times the spikelet length; culms branched

* C. purpureus  (NSW NT  SA WA QLD) 

Pennisetum purpureum

Key to Cenchrus derived from De Lisle 1963, Vickery 1975 (Cenchrus s.s and Pennisetum),  Webster 1987  (Cenchrus s.s and Pennisetum) .  Nomenclature from Chemisquy et al 2010.


Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith