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Genus Cenchrus Family Poaceae

Description: Tufted or rhizomatous annuals or perennials.

Leaves with ligule a ciliate membranous rim; blade flat or involute; sheath compressed.

Inflorescence a terminal spike-like panicle or raceme of 'burrs' enclosing the spikelets.

Spikelets in groups of 1–5, enclosed by a ring or involucre of bristles (1 bristle often longer than the others), with their bases at least partly fused forming a cup-like structure, or the bristles thickened and fused to form a spiny burr the bristles falling with the spikelets; florets 1 or 2, the upper bisexual, the lower sterile or male. Lower glume minute, the upper equalling the spikelet. Lower lemma similar in texture to the glumes, the upper hardened. Paleas firm, similar in texture to their lemmas, the lower sometimes absent.

Distribution and occurrence: World: c. 30 species, mainly in warm dry regions of Africa, America & SW Asia. Australia: c. 10 species (4 species native), all mainland States.

Recent research has shown that Pennisetum is more appropriately amalgamated with Cenchrus - see Chemisquy et al. (2010) and references therein. We will be making this change once all of the relevant names have been published.

Text by S. W. L. Jacobs & S. M. Hastings (1993); edited KL Wilson (Sept 2010)
Taxon concept:

Taxa not yet included in identification key
Cenchrus americanus,    Cenchrus clandestinus,    Cenchrus longisetus,    Cenchrus macrourus,    Cenchrus purpurascens,    Cenchrus purpureus,    Cenchrus setaceus,    Cenchrus spinifex

 Key to the species 
1Spines or bristles fused for 25% or less of their length from the base, forming a small disc or shallow cup at the base of the burr2
Spines or bristles fused for 25% or more of their length from the base, forming a ± globular burr or involucre enclosing 1-several spikelets5
2Burr 5–11 mm long, bristles retrorsely barbed, burrs often dark purplish black3
Burr c. 12 mm long, with one bristle longer than the others, bristles antrorsely barbed, inner bristles ciliate in the lower part
                       Back to 1
3Spikelets 7 mm long or less, rarely exceeding the 4–7 mm long bristles; cupule at the base of the involucre usually well developed; spikelets tending to diverge from the c. 1 mm diameter axis at maturityCenchrus caliculatus
Spikelets 9 mm long or more, usually exceeding the 7–9 mm long involucral bristles; cupule well developed, often one-sided; rachis >1 mm in diam., spikelets not diverging at maturity
                       Back to 2
Cenchrus robustus
4Inner bristles of involucre fused only at the base forming a short disc, otherwise free, bristles forming an uninterrupted ring; a variable speciesCenchrus ciliaris
Inner bristles of involucre fused at the base for 1–3 mm to form a shallow, often oblique cup, burr usually deeply cleft on one side
                       Back to 2
Cenchrus pennisetiformis
5Burr consisting of an inner whorl of fused, flattened bristles or spines subtended by at least one whorl of shorter, finer bristles often united only at the base6
Burr consisting of several whorls of flattened spines fused into a cleft, cup-like structure with spines protruding at regular intervals; ring(s) of smaller bristles absent
                       Back to 1
6Bristles retrorsely barbed; burr 4–10 mm long, 3.5–6 mm wide; bristles often tinged with purple at the tipsCenchrus echinatus
Bristles antrorsely barbed; burr 3–7 mm long, 1.5–4 mm wide, not purple tinged
                       Back to 5
Cenchrus setiger
7Spikelets 6–7 mm long protruding from the burr which is made up of 40–70 spines; burrs with one deep cleft and sometimes purple-tingedCenchrus longispinus
Spikelets 4.5–5.5 mm long their tips scarcely protruding beyond the burr which is made up of <40 spines; burrs with two deep clefts; rarely purple-tinged
                       Back to 5
Cenchrus incertus

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