| # The grass genera of the world |

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

### Pennisetum Rich.

From the Latin penna (feather) and seta (bristle), alluding to the inflorescence.

~ Cenchrus

Type species: Type: P. typhoideum (L.) Rich. = P. glaucum (L.) R.Br.

Including Amphochaeta Anderss., Catatherophora Steud., Eriochaeta Fig. & De Not, Gymnotrix P. Beauv., Loydia Delile, Macrochaeta Steud., Penicillaria Willd., Pentastachya Steud., Sericura Hassk.

Excluding Beckeropsis, Pseudochaetochloa

Habit, vegetative morphology. Annual (rarely), or perennial; stoloniferous, or caespitose, or decumbent. Culms 15–800 cm high; herbaceous; branched above, or unbranched above. The branching suffrutescent, or simple (mostly), or fastigiate. Culm leaf sheaths compressed (usually), or keeled, or rounded. Culm internodes solid, or hollow. Young shoots extravaginal, or intravaginal, or extravaginal and intravaginal. Leaves mostly basal, or not basally aggregated; auriculate, or non-auriculate. Leaf blades broad, or narrow; 3–35(–50) mm wide (and up to 1 m or more long in some species); not pseudopetiolate; without cross venation; disarticulating from the sheaths, or persistent; rolled in bud, or once-folded in bud. Ligule a fringed membrane to a fringe of hairs. Contra-ligule present (of hairs), or absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant, or all alike in sexuality; hermaphrodite, or hermaphrodite and male-only (peripheral spikelets of the glomerules may be male-only); overtly heteromorphic (section Hetercetachya, where the outer, male spikelets are laterally compressed and keeled, with larger upper glume and lower lemma), or homomorphic (mostly). Plants outbreeding; with hidden cleistogenes (e.g. P. clandestinum, which lacks ‘normal’ inflorescences), or without hidden cleistogenes. The hidden cleistogenes when present, in the leaf sheaths. Apomictic, or reproducing sexually.

Inflorescence. Inflorescence a false spike, with spikelets on contracted axes, or paniculate (the spikelets fascicled in false spikes, in small groups or apparently solitary, but always surrounded at their bases by reduced-branch bristles); contracted (into false spikes). Primary inflorescence branches inserted all around the main axis. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes very much reduced (to one or few spikelets plus bristles); disarticulating (but the main axis persistent); falling entire (the false spikes or spikelet-plus-bristle clusters falling). Spikelets with ‘involucres’ of ‘bristles’ (these sessile to shortly stalked, the bristles relatively slender, basally free or scarcely united, by contrast with Cenchrus). The ‘bristles’ relatively slender, not spiny; deciduous with the spikelets. Spikelets secund (when the inflorescence is branched), or not secund; subsessile, or pedicellate; not in distinct ‘long-and-short’ combinations.

Female-fertile spikelets. Spikelets compressed dorsiventrally (to subterete); falling with the glumes, or disarticulating above the glumes and falling with the glumes, or not disarticulating (in cultivated forms); not disarticulating between the florets, or disarticulating between the florets (i.e the upper floret sometimes readily disarticulating from the rest of the spikelet). Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; very unequal (G1 often minute or vestigial); shorter than the adjacent lemmas, or long relative to the adjacent lemmas (G2 very short to as long as the spikelet); free; awnless; very dissimilar, or similar (hyaline or membranous). Lower glume 0–5 nerved. Upper glume 0–11 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate, or epaleate. Palea of the proximal incomplete florets when present, fully developed to reduced. The proximal incomplete florets male, or sterile. The proximal lemmas awnless; 3–9(–15) nerved; exceeded by the female-fertile lemmas to more or less equalling the female-fertile lemmas (mostly), or decidedly exceeding the female-fertile lemmas (section Brevivalvula); less firm than the female-fertile lemmas to similar in texture to the female-fertile lemmas (membranous); not becoming indurated.

Female-fertile florets 1. Lemmas similar in texture to the glumes to decidedly firmer than the glumes; smooth, or striate; not becoming indurated (membranous to chartaceous or subleathery, the texture hardened or unchanged at maturity); white in fruit, or yellow in fruit; entire; pointed, or blunt; awnless, or mucronate; hairy (near the margins), or hairless (glabrous); non-carinate; having the margins lying flat on the palea; with a clear germination flap; 5–7 nerved. Palea present; relatively long; entire; awnless, without apical setae; textured like the lemma (apart from the thinner margins); not indurated; 2-nerved. Lodicules present (then often very minute), or absent; when present, 2; glabrous. Stamens 3. Anthers penicillate (conspicuously so in section Penicillaria), or not penicillate. Ovary apically glabrous. Styles fused, or free to their bases. Stigmas 2; white.

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 long mesocotyl. First seedling leaf with a well-developed lamina. The lamina broad; erect, or curved; 21–30 veined.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; (30–)33–70(–102) microns long; (5.4–)6–6.9(–7.2) microns wide at the septum. Microhair total length/width at septum 4.5–6.1. Microhair apical cells (18.6–)21–46(–54) microns long. Microhair apical cell/total length ratio 0.53–0.73. Stomata common; 24–25.5–27 microns long. Subsidiaries triangular, or dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies tall-and-narrow, or vertically elongated-nodular. Costal short-cells predominantly paired, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies ‘panicoid-type’; cross shaped, or butterfly shaped, or dumb-bell shaped, or nodular; not sharp-pointed.

Transverse section of leaf blade, physiology. C4; biochemical type NADP–ME (2 species); XyMS–. PCR sheath outlines uneven. PCR sheath extensions absent. PCR cell chloroplasts with reduced grana; centrifugal/peripheral. Mesophyll with radiate chlorenchyma; without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs, or ‘nodular’ in section, or adaxially flat; with the ribs very irregular in sizes. Midrib conspicuous; with one bundle only, or having a conventional arc of bundles; with colourless mesophyll adaxially (this sometimes mirrored by adaxial colourless tissue above the lateral vacular bundles), 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 containing flavonoid sulphates (some material only of 1 species), or without flavonoid sulphates (2 species).

Cytology. Chromosome base number, x = 9. 2n = 14, 18, 22, 34, 35, 36, 45, 52, and 54, or 32–54. Chromosomes ‘small’. Haploid nuclear DNA content 0.6–2.5 pg (2 species, 2x and 4x).

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Cenchrinae. About 80 species.

Distribution, phytogeography, ecology. In warm regions.

Commonly adventive. Helophytic, mesophytic, and xerophytic; shade species and species of open habitats. Savanna, woodland, weedy ground.

Economic aspects. Significant weed species: P. alopecuroides, P. americanum, P. clandestinum, P. pedicellatum, P. polystachyon, P. purpureum, P. setaceum, P. sieberianum (in P. glaucum), P. villosum. Cultivated fodder: P. clandestinum (Kikuyu), P. purpureum (Elephant). Important native pasture species: P. donsonii, P. massaicum, P. trachyphyllum etc. Grain crop species: P. glaucum (Pearl Millet - the most drought tolerant tropical cereal). Lawns and/or playing fields: P. clandestinum.

Rusts and smuts. Rusts — Phakopsora and Puccinia. Taxonomically wide-ranging species: Puccinia chaetochloae, Puccinia stenotaphri, Puccinia levis, Puccinia substriata, ‘Uromyces’ setariae-italicae, and Puccinia esclavensis. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae — Tilletia. Ustilaginaceae — Sorosporium, Sphacelotheca, Tolyposporium, and Ustilago.

References, etc. Leaf anatomical: Metcalfe 1960; studied by us - P. alopecuroides (L.) Sprengel, P. villosum R. Br.

Special comments. Some of the species closely approach Cenchrus.

Illustrations. • Pennisetum basedowii: Hook. Ic. Pl. 32 (1933). • Pennisetum basedowii: Gardner, 1952. • Pennisetum polystachion (as P. borbonicum): Kunth (1835), Dist. méthodique de la famille Graminées. • Pennisetum purpureum: Fl. W. Trop. Afr. (1936). • Clandestine inflorescence (Pennisetum clandestinum). • Clandestine spikelets of Pennisetum clandestinum. • General aspect of Pennisetum setaceum. • General aspect of Pennisetum sphacelatum: Gibbs Russell et al., 1990. • Falsely-spicate Inflorescence of Pennisetum alopecuroides. Pennisetum alopecuroides. A false spike of bristly-involucrate glomerules. • Spikelike inflorescence of Pennisetum glaucum. Pennisetum glaucum. A dense spikelike inflorescence of bristly-involucrate spikelet clusters. • Spikelet glomerule with involucre of bristles (Pennisetum villosum). Pennisetum villosum. Glomerule with involucre of bristles. • Pennisetum villosum, abaxial epidermis of leaf blade: this project. • T.S. leaf blade of Pennisetum typhoides, fluorescence image: this project. • Pennisetum villosum, T.S. leaf blade fluorescence image: this project. • Pennisetum villosum, T.S. leaf blade midrib zone: this project. • Pennisetum villosum, T.S. leaf blade with immunofluorescent-labelled Rubisco (Hattersley, Watson and Osmond 1977). Immunofluorescent-labelled Rubisco confined to the (centrifugal) sheath cell chloroplasts. See Hattersley, Watson and Osmond (1977). • Grass pollen antigens: Watson and Knox (1976).

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, and classifications. See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., Macfarlane, T.D., and Dallwitz, M.J. 1992 onwards. The 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. Version: 15th June 2025. delta-intkey.com’.

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