Cenchrus L.
From the Greek kegchros (millet, Panicum miliaceum).
Including Echinaria Fabric., Nastus Lunell, Raram Adans.
Habit, vegetative morphology. Annual, or perennial (‘sand-burrs’); rhizomatous, or stoloniferous, or caespitose, or decumbent. Culms 5–100(–150) cm high; herbaceous; branched above. Culm nodes glabrous. Culm internodes solid, or hollow. Leaves not basally aggregated; non-auriculate. Leaf blades linear, or linear-lanceolate; narrow; flat, or folded; without cross venation; persistent; rolled in bud; a fringed membrane to a fringe of hairs.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite, or hermaphrodite and sterile (if the ‘bristles’ are taken to include vestigial spikelets). Apomictic, or reproducing sexually.
Inflorescence. Inflorescence a false spike, with spikelets on contracted axes (the spikelets in prickly glomerules (burrs) composed of coalescing spines representing modified branchlets). Primary inflorescence branches inserted all around the main axis. Rachides angular or compressed. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes very much reduced (to burrs); disarticulating (but the main axis persistent); falling entire (i.e., the burrs falling). Spikelets with ‘involucres’ of ‘bristles’ (the bristles coalescing, by contrast with Pennisetum). The ‘bristles’ nearly always spiny, markedly coalescent basally (not spiny, merely ciliate, in C. ciliaris); deciduous with the spikelets. Spikelets not secund.
Female-fertile spikelets. Spikelets lanceolate, or ovate; compressed dorsiventrally; falling with the glumes (i.e., in the burrs). Rachilla terminated by a female-fertile floret. Hairy callus absent.
Glumes present; two; very unequal; shorter than the adjacent lemmas, or long relative to the adjacent lemmas; awnless; very dissimilar, or similar (hyaline or membranous). Lower glume 1–5 nerved. Upper glume 1–7 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets paleate, or epaleate (rarely). Palea of the proximal incomplete florets fully developed, or reduced (rarely). The proximal incomplete florets male, or sterile. The proximal lemmas awnless; 1–7 nerved; more or less equalling the female-fertile lemmas; less firm than the female-fertile lemmas; not becoming indurated.
Female-fertile florets 1. Lemmas similar in texture to the glumes to decidedly firmer than the glumes (firmly membranous, dull, papery or leathery); smooth; not becoming indurated; yellow in fruit; entire; awnless; hairless; non-carinate; having the margins lying flat on the palea; with a clear germination flap; 3–7 nerved. Palea present; relatively long; entire; awnless, without apical setae; textured like the lemma; not indurated; 2-nerved. Lodicules absent. Stamens 3. Anthers not penicillate. Ovary glabrous. Styles fused, or free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit small; compressed dorsiventrally. Hilum short. Embryo large; waisted. Endosperm hard; without lipid; containing only simple starch grains. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.
Seedling with a short mesocotyl. First seedling leaf with a well-developed lamina. The lamina broad; curved; 21–30 veined.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls, or having straight or only gently undulating walls. Microhairs present; panicoid-type; (45–)54–84(–114) microns long; 6–11.5(–12.6) microns wide at the septum. Microhair total length/width at septum 6–10(–11.6). Microhair apical cells (27–)30–60(–72) microns long. Microhair apical cell/total length ratio 0.5–0.69. Stomata common; 30–45 microns long, or 36–52 microns long (C. echinatus). Subsidiaries markedly triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common, or absent or very rare. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped, or butterfly shaped, or dumb-bell shaped.
Transverse section of leaf blade, physiology. C4; biochemical type NADP–ME (C. pauciflorus, C. incertus); XyMS–. PCR sheath outlines uneven. PCR sheath extensions absent. PCR cells with a suberised lamella. PCR cell chloroplasts with reduced grana; centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Midrib conspicuous; having a conventional arc of bundles; with colourless mesophyll adaxially, or without colourless mesophyll adaxially (rarely). Bulliforms present in discrete, regular adaxial groups; in simple fans, or in simple fans and associated with colourless mesophyll cells to form deeply-penetrating fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present, or absent; nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.
Culm anatomy. Culm internode bundles scattered.
Phytochemistry. Leaves without flavonoid sulphates (1 species).
Cytology. Chromosome base number, x = 9 and 12. 2n = 34, 35, 36, 40, 44, 45, and 68. Chromosomes ‘small’. Mean diploid 2c DNA value 2.6 pg (?-ploidy of the one species studied unknown).
Taxonomy. Panicoideae; Panicodae; Paniceae.
Distribution, ecology, phytogeography. 22 species; tropical and warm temperate. Commonly adventive. Mesophytic to xerophytic; shade species, or species of open habitats; halophytic, or glycophytic. Grassland, bush, sandy and weedy places.
Holarctic, Paleotropical, Neotropical, Australian, and Antarctic. Boreal, Tethyan, and Madrean. African, Madagascan, Indomalesian, Polynesian, and Neocaledonian. Atlantic North American and Rocky Mountains. Macaronesian, Mediterranean, and Irano-Turanian. Saharo-Sindian, Sudano-Angolan, West African Rainforest, and Namib-Karoo. Indian, Indo-Chinese, Malesian, and Papuan. Hawaiian and Fijian. Caribbean, Venezuela and Surinam, Amazon, Central Brazilian, Pampas, and Andean. North and East Australian. New Zealand. Canadian-Appalachian, Southern Atlantic North American, and Central Grasslands. Sahelo-Sudanian, Somalo-Ethiopian, South Tropical African, and Kalaharian. Tropical North and East Australian.
Rusts and smuts. Rusts — Puccinia. Smuts from Ustilaginaceae. Ustilaginaceae — Sorosporium, Sphacelotheca, Tolyposporium, and Ustilago.
Economic importance. Significant weed species: C. biflorus, C. brownii, C. ciliaris, C. echinatus, C. incertus, C. longispinus, C. myosuroides, C. pauciflorus, C. tribuloides. Cultivated fodder: C. ciliaris (drought resistant, tolerant of heavy grazing), C. setiger. Important native pasture species: C. biflorus, C. ciliaris, C. pennisetiformis, C. setigerus.
References, etc. Leaf anatomical: Metcalfe 1960 and this project.
Special comments. Some species overlapping with Pennisetum.
Illustrations. • General aspect. • General aspect. • Ligule region. • Inflorescence detail. Cenchrus ciliaris , spikelet clusters. • A spikelet cluster. Cenchrus ciliaris, a spikelet cluster subtended by ‘bristles’. • Spikelet clusters. Cenchrus setiger. • Rachis and abscising spikelet clusters. Cenchrus setiger. • Old spikelet cluster. Cenchrus setiger. • Spikelet cluster. Cenchrus longispinus. • Germination flap. Cenchrus echinatus. • Abaxial epidermis of leaf blade
Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘Grass Genera of the World: Descriptions, Illustrations, Identification, and Information Retrieval; including Synonyms, Morphology, Anatomy, Physiology, Phytochemistry, Cytology, Classification, Pathogens, World and Local Distribution, and References.’ http://biodiversity.uno.edu/delta/. Version: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).
