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)
Taxa not yet included in identification key
| ||Key to the species|| |
|1||Spines 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 burr||2|
|Spines or bristles fused for 25% or more of their length from the base, forming a ± globular burr or involucre enclosing 1-several spikelets||5|
|2||Burr 5–11 mm long, bristles retrorsely barbed, burrs often dark purplish black||3|
|Burr c. 12 mm long, with one bristle longer than the others, bristles antrorsely barbed, inner bristles ciliate in the lower part|
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|3||Spikelets 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 maturity||Cenchrus 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|
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|4||Inner bristles of involucre fused only at the base forming a short disc, otherwise free, bristles forming an uninterrupted ring; a variable species||Cenchrus 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|
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|5||Burr 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 base||6|
|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|
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|6||Bristles retrorsely barbed; burr 4–10 mm long, 3.5–6 mm wide; bristles often tinged with purple at the tips||Cenchrus echinatus|
|Bristles antrorsely barbed; burr 3–7 mm long, 1.5–4 mm wide, not purple tinged|
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|7||Spikelets 6–7 mm long protruding from the burr which is made up of 40–70 spines; burrs with one deep cleft and sometimes purple-tinged||Cenchrus 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|
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