| # The grass genera of the world |

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

### Panicum L.

Panicum: old Latin name for common millet (Setaria italica).

Panics.

Type species: Type: P. miliaceum L.

Including Chasea Nieuw., Coleataenia Griseb., Dileucaden (Raf.) Steud., Eatonia Raf., Eriolytrum Kunth, Hopia (Kunth) Zuloagas & Morrone, Milium Adans., Monachne P. Beauv., Polyneura Peter, Psilochloa Launert, Setiacis sensu lato Chen & Y.X. Jin (?- original description inadequate), Sorengia, Stephostachys (= P. mertensii), Trichanthecium Zuloaga & Morrone

Excluding Apochloa Zuloaga & Morrone, Cyphonanthus (= P. discrepans), Dichanthelium, Hopia Zuloaga & Morrone, Morronea Scataglini, Parodiophyllochloa Zuloaga & Morrone, Renvoizea Zuloaga & Morrone, Rugoloa Zuloaga, Steinchisma, Thedachloa S.W. Jacobs, Walwhalleya K.E. Wills & J.J. Bruhl, Zuloagaea (~ P. bulbosum)

Habit, vegetative morphology. Annual, or perennial (but no overwintering rosette - by contrast with Dichanthelium); rhizomatous, or stoloniferous, or caespitose, or decumbent. Culms 20–400 cm high; woody and persistent, or herbaceous; self-supporting; branched above, or unbranched above. The branching suffrutescent, or simple (mostly), or fastigiate. Culms tuberous (rarely), or not tuberous. Culm nodes hairy, or glabrous. Culm leaf sheaths compressed, or rounded. Culm internodes solid, or hollow (usually). Plants with multicellular glands (rarely, then stalked, e.g. in the Clavelligera group), or without multicellular glands (usually). Leaves mostly basal, or not basally aggregated; auriculate (rarely), or non-auriculate. Leaf blades broad, or narrow; cordate, or not cordate, not sagittate; setaceous (rarely), or not setaceous; flat (usually); pseudopetiolate (rarely), or not pseudopetiolate; without cross venation; disarticulating from the sheaths (occasionally), or persistent; rolled in bud. Ligule an unfringed membrane, or a fringed membrane (rarely reduced to a hair fringe elsewhere than in Australia?). Contra-ligule present (of hairs), or absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets; inbreeding; exposed-cleistogamous, or chasmogamous. Apomictic, or reproducing sexually.

Inflorescence. Inflorescence paniculate (except in the Stolonifera group and some species of section Laxa, where it consists of racemes and the distiction from Urochloa (Brachiaria sensu lato) breaks down); deciduous in its entirety, or not deciduous; open, or contracted; with capillary branchlets, or without capillary branchlets. Primary inflorescence branches inserted all around the main axis. Inflorescence with axes ending in spikelets. Rachides at least in in Panicum sensu stricto triquetrous or filiform, neither flattened nor hollowed, not winged. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. The racemes spikelet bearing to the base, or without spikelets towards the base. Spikelet-bearing axes persistent. Spikelets not secund (generally, at least in Panicum sensu stricto,), or secund (e.g., in the American Agrostoidea group, ‘Psilochloa’, some species in section Laxa, etc.); pedicellate. Pedicel apices cupuliform.

Female-fertile spikelets. Spikelets 1.4–6 mm long; elliptic, or lanceolate, or ovate, or obovate; in the few cases where the orientation is ascertainable, abaxial, or adaxial; not noticeably compressed to compressed dorsiventrally (only rarely weakly lateraly compressed, mainly in segregate genera); (usually, at least in Panicum sensu stricto), biconvex, or planoconvex (in some small segregates?); falling with the glumes, or not disarticulating; with conventional internode spacings, or with a distinctly elongated rachilla internode between the glumes, or with distinctly elongated rachilla internodes between the florets, or with a distinctly elongated rachilla internode between the glumes and with distinctly elongated rachilla internodes between the florets. The upper floret conspicuously stipitate (e.g. section Rudgeana), or the upper floret not stipitate. The stipe beneath the upper floret when present, not filiform; straight and swollen; heterogeneous (section Rudgeana), or homogeneous. Rachilla terminated by a female-fertile floret (very rarely prolonged, e.g. occasionally in P. heliophilum: Zuloaga and Morone 1991). Hairy callus absent.

Glumes two; nearly always very unequal; (the longer) long relative to the adjacent lemmas; without conspicuous tufts or rows of hairs (at least, without the transverse row characterizing the lower glume of Yakirra?); nearly always awnless (the G2 truncate to pointed, very rarely shortly awn-tipped); very dissimilar, or similar (herbaceous-membranous, the lower sometimes very short and nerveless). Lower glume 0.15–0.8 times the length of the upper glume; much shorter than half length of lowest lemma to longer than half length of lowest lemma; 1–7 nerved. Upper glume 3–9 nerved. Spikelets nearly always with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets nearly always 1 (rarely 2); paleate, or epaleate. Palea of the proximal incomplete florets when present, fully developed to reduced; not becoming conspicuously hardened and enlarged laterally. The proximal incomplete florets male, or sterile (e.g., in Morronea). The proximal lemmas awnless; 3 nerved (rarely), or 5–9 nerved, or 11 nerved (rarely); more or less equalling the female-fertile lemmas to decidedly exceeding 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; smooth (rarely rugose: subgenus Megathyrsus (~ P. maximum)); becoming indurated to not becoming indurated (leathery, bony or cartilaginous, usually becoming indurated, but membranous in a few species of section Laxa, associated with other morphological peculiarities); yellow in fruit, or brown in fruit; entire; pointed, or blunt; usually not crested; awnless (rarely minutely apiculate); hairy (rarely, e.g. in Morronea), or hairless; non-carinate; having the margins inrolled against the palea (nearly always, but no doubt there are exceptions among the forms with non-indurated lemmas); with a clear germination flap; mostly obscurely 3–11 nerved. Palea present; relatively long; tightly clasped by the lemma (except in P. discrepans, where it is free at the tip); entire; awnless, without apical setae; textured like the lemma; indurated, or not indurated; 2-nerved. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers 0.3–2 mm long; not penicillate. Ovary apically glabrous; without a conspicuous apical appendage. Styles free to their bases. Stigmas 2; red pigmented.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small; compressed dorsiventrally. Hilum nearly always short (but linear in (e.g.) P. glutinosum, P. macranthum, P. pilgerianum = Psilochloa). Embryo large. Endosperm hard; without lipid; containing only simple starch grains, or containing compound 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; 6–12 veined.

Ovule, embryology. Micropyle not noticeably oblique. Outer integument covering no more than the chalazal half of the ovule; two cells thick at the micropylar margin. Inner integument discontinuous distally; not thickened around the micropyle. Synergids not haustorial; without large, globular starch grains.

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. Intercostal zones with typical long-cells, or exhibiting many atypical long-cells, or without typical long-cells. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; clearly two-celled (nearly always), or uniseriate (3(-4) celled in P. validum, Zuloaga et al. 1989); panicoid-type; without ‘partitioning membranes’ (in P. virgatum); (38–)42–78(–85) microns long; (5.4–)6–6.3(–6.6) microns wide at the septum. Microhair total length/width at septum 6.3–9. Microhair apical cells (25.5–)26–48(–55) microns long. Microhair apical cell/total length ratio 0.57–0.62. Stomata common; 30–33 microns long. Subsidiaries low dome-shaped, or triangular, or dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common, or absent or very rare; in cork/silica-cell pairs, or not paired (solitary); silicified, or not silicified. Intercostal silica bodies when present, cross-shaped, or rounded, or tall-and-narrow. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’, or tall-and-narrow to crescentic (rarely); mostly cross shaped to dumb-bell shaped, or nodular; not sharp-pointed.

Transverse section of leaf blade, physiology. C4 (in Panicum sensu stricto, with C3 species continuing to be removed to segregate genera). The anatomical organization conventional, or unconventional. Organization of PCR tissue in a few species Alloteropsis type. Biochemical type PCK (5 species), or NAD–ME (14 species, with some of these exhibiting ‘PCK-like’ leaf blade anatomy), or NADP–ME (4 species); XyMS+, or XyMS–. PCR sheath outlines uneven, or even. PCR sheath extensions present (rarely), or absent (usually). Maximum number of extension cells when present, 1. PCR cells with a suberised lamella, or without a suberised lamella. PCR cell chloroplasts ovoid, or elongated; with well developed grana, or with reduced grana; centrifugal/peripheral, or centripetal. Mesophyll with radiate chlorenchyma; Isachne-type, or not Isachne-type; traversed by columns of colourless mesophyll cells, or not traversed by colourless columns. Leaf blade ‘nodular’ in section, or adaxially flat; with the ribs more or less constant in size, or with the ribs very irregular in sizes. Midrib conspicuous, or not readily distinguishable; with one bundle only, or having a conventional arc of bundles; with colourless mesophyll adaxially, or without colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; in simple fans and associated with colourless mesophyll cells to form deeply-penetrating fans (sometimes linking with traversing columns of colourless cells). Many of the smallest vascular bundles unaccompanied by sclerenchyma, or all the vascular bundles accompanied by sclerenchyma (rarely). Combined sclerenchyma girders present; forming ‘figures’, or nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Phytochemistry. Tissues of the culm bases with abundant starch. Leaves containing flavonoid sulphates (2 species), or without flavonoid sulphates (8 species). Leaf blade chlorophyll a:b ratio 3.2–3.56 (PCK), or 3.5–4.82 (NAD-ME), or 3.86–4.64 (NADP-ME).

Special diagnostic feature. Plants not as in Dichanthelium (q.v.).

Cytology. Chromosome base number, x = 7, 9, and 10. 2n = 18 (seemingly rarely), or 36, or 37, or 54, or 72. Chromosomes ‘small’. Haploid nuclear DNA content 0.5 pg (1 species, 6x). Nucleoli persistent.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Melinidinae (Megathyrsus only), or Panicinae (mostly, still), or Arthropogoninae (e.g., Stephostachys). About 370 species.

Distribution, phytogeography, ecology. Tropical, subtropical and warm temperate.

Commonly adventive. Mesophytic, or xerophytic; shade species and species of open habitats; halophytic (rarely), or glycophytic. Diverse habitats: P. pinifolium sandbinding.

Economic aspects. Significant weed species: P. antidotale, P. barbipulvinatum, P. bisulcatum, P. brevifolium, P. capillare, P. dichotomoflorum, P. gattingeri, P. laevifolium, P. maximum, P. miliaceum, P. natalense, P. obtusum, P. repens, P. sarmentosum, P. trichoides, P. turgidum, P. virgatum, etc. Cultivated fodder: P. coloratum (Buffalo), P. maximum (Guinea grass), P. miliaceum, P. purpurascens, P. schinzii. Important native pasture species: many species, e.g. P. coloratum, P. maximum, P. merkeri, P. obtusum, P. poaeoides, P. repens, P. stipitatum, P. trichocladum, P. trichoides, P. texanum, P. virgatum. Grain crop species: P. miliaceum (Proso millet); also P. sonorum (Sauwi), P. sumatrense (Sama).

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia dolosa, ‘Uromyces’ setariae-italicae, and Puccinia esclavensis.

References, etc. Morphological/taxonomic: Hitchcock and Chase 1910, 1915; Hsu 1965; Brown 1977; Zuloaga and Soderstrom 1985; Zuloaga 1987; Ellis 1988. Leaf anatomical: Metcalfe 1960; studied by us - P. antidotale Retz, P. bulbosum H.B.K., P. buncei F. Muell. ex Benth., P. cambogiense Balansa, P. coloratum L., P. effusum R. Br., P. incomtum Trin., P. laevifolium Hack., P. maximum Jacq., P. miliaceum L., P. mitchellii Benth., P. paludosum Roxb., P. pygmaeum R. Br., . simile Domin, P. subxerophyllum Domin, P. trachyrhachis Benth.

Special comments. Generic limits among the relatives of Panicum (Ancistrachne, Brachiaria, Dichanthelium, Digitaria, Eriochloa, Homolepis, Hylebates, Hymenachne, Ichnanthus, Paspalidium, Sacciolepis, Setaria, Tricholaena, Urochloa, Whiteochloa etc., and many small segregates) need critical revision in terms of comparative data recorded at world level. W. V. Brown (1977) expounded on the problem 1n 1977, and Zuloaga embarked on a detailed treatment of the New World species in 1982. Subsequent re-alignments of species (e.g., Webster (1987), Webster et al (1994), Morrone et al. (2007, 2008), Sede et al. (2008), Scataglini and Zuloaga (2013)) continue to reduce the variability here attributed to Panicum, but by 2016 a sensu stricto version permitting convincing diagnosis and practical applicationhas yet to be delimited. Occasional species with a rachilla prolongation or a second sterile floret, and small suites of species with laterally compressed spikelets, secund one-sided inflorescence branches, stipitate upper florets, linear hila, etc., pose major hazards for printed generic keys; and for use in that context, the description of Panicum as encoded here will generally require editing at regional level. The agriculturally important species P. maximum well illustrates the situation. It may belong with species currently referred to Urochloa and/or Brachiaria (PCK, rugose upper lemma, etc.), but changes of this kind will not be effectively implemented until the generic circumscriptions have been clarified.

Illustrations. • Panicum aequinerve: Wood, Natal Plants 2 (1904). • Panicum aquaticum, with Morronea arundinariae as Panicum Pohl, Flora Costaricensis (1980). • Panicum decompositum and P. effusum: Turner, Austr. Grasses (1895). • Panicum deustum: Wood, Natal Plants 2 (1904). • Panicum laticomum: Wood, Natal Plants 2 (1904). • Panicum maximum: Fl. W. Trop. Afr. (1936). • Panicum maximum: Wood, Natal Plants 2 (1904). • General aspect (Panicum maximum): Gibbs Russell et al., 1990. • Panicum maximum, as Megathyrsus: Sanchez-Ken, Flora del Valle Tehuacán-Cuicatlan (2011). • Panicum miliaceum: Lamson-Scribner (1890). • Panicum pilosum, as P. monostachyum: Kunth (1835). • Panicum repens: Bor, Flora of Iraq (1968). • Bulbous culm base (Panicum bulbosum, ~ Zuloagaea). • Ligule of Panicum kalaharense. • Inflorescence detail of Panicum antidotale. • Inflorescence and spikelet of Panicum decompositum: E. Hickman. • Spikelet and floret of Panicum decompositum: E. Hickman. • Spikelet and flower of Panicum decompositum: E. Hickman. • Inflorescence base (immature) of Panicum effusum. • Inflorescence pulvinus (Panicum effusum). • Spikelets of Panicum effusum. • Spikelet of Panicum laevifolium in close-up. • Inflorescence of Panicum stapfianum. • Panicum stapfianum, spikelet with parts displayed in detail: this project. Panicum stapfianum. Opened, showing short G1 (bottom right) and long G2 (left); long lemma of the lower, male floret (right, resembling G2, anther tips visible); and long, thin palea. Upper hermaphrodite floret with short, shiny, indurated lemma and palea, exhibiting stamens and stigmas. • Opened spikelet of Paicum effusum. • Seedling of Panicum laevifolium. • Seedlings of Panicum milioides. • Panicm bulbosum, ~Zuloagaea), T.S. leaf blade (fluorescence image). • Panicum pygmaeum, T.S. leaf blade (fluorescence image). • Panicum pygmaeum, T.S. leaf blade with immunofluorescent-labelled Rubisco (Hattersley, Watson and Osmond 1977). Exhibiting immunofluorescent-labelled Rubisco throughout the chlorophyllous mesophyll. • Panicum effusum, leaf blade transverse section. • Panicum miliaceum, leaf blade transverse section. • Panicum bulbosum (~Zuloagaea), leaf blade transverse section. • Leaf blade T.S.: immunofluorescent-labelled Rubisco in Panicum milioides (Hattersley, Watson and Osmond 1977). This C3-C4 intermediate species exhibits C3-like occurrence of Rubisco in both sheath and mesophyll chloroplasts. See Hattersley, Watson and Osmond (1977). • Panicum milioides, T.S. leaf blade (fluorescence image). See Hattersley, Watson and Osmond (1977). • Panicum effusum, leaf blade T.S., electron micrograph of PCR cell. Panicum effusum. C4 type NAD-ME. • Panicum maximum, leaf blade T.S., electron micrograph of PCR cell. Panicum maximum. C4 type PCK. • ‘Panicoid-type’ microhairs of Panicum virgatum and Eragrostis elongata: longitudinal EM sections (Amarasinghe). Longitudinal sections showing ultrastructural details of ‘panicoid-type’ microhairs: 21–22, Panicum virgatum; 23–25, Eragrostis elongata. BC = basal cell, CC = cap cell, CW = cell wall, CH = cuticular chamber, D = dictyosomes, M = mitochondria, N = nucleus, OS = osmophilic material, P = plastids, RER = rough endoplasmic reticulum, VC = vacuole; scale bar = 1.5 microns.

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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