Panicum L.
Panicum: old Latin name for common millet (Setaria italica).
Including Chasea Nieuw., Coleataenia Griseb., Dileucaden (Raf.) Steud., Eatonia Raf., Eriolytrum Kunth, Milium Adans., Monachne P. Beauv., Phanopyrum (Raf.) Nash, Polyneura Peter, Psilochloa Launert, Setiacis S.L. Chen & Y.X. Jin (?- original description inadequate)
Excluding Dichanthelium, Steinchisma
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; branched above, or unbranched above; tuberous (rarely), or not tuberous. Culm nodes hairy, or glabrous. Culm internodes solid, or hollow. Plants with multicellular glands (rarely, then stalked, e.g. in the Clavelligera group), or without multicellular glands (usually). The shoots not aromatic. 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; an unfringed membrane, or a fringed membrane to a fringe of hairs. Contra-ligule present (of hairs), or absent.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality. Plants inbreeding; exposed-cleistogamous, or chasmogamous; without hidden cleistogenes. 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. Rachides hollowed, or flattened, or winged, or 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 (except in the American Agrostoidea group, ‘Psilochloa’, some species in section Laxa, etc.); pedicellate. Pedicel apices cupuliform. Spikelets not in distinct ‘long-and-short’ combinations.
Female-fertile spikelets. Spikelets 1.4–6 mm long; elliptic, or lanceolate, or ovate, or obovate; adaxial (in the few cases where the orientation is ascertainable); compressed dorsiventrally (with very few exceptions: e.g. P. hemitomum); 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. sections Phanopyrum, 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 present; two; nearly always very unequal; (the longer) long relative to the adjacent lemmas; without conspicuous tufts or rows of hairs; 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. 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 feww 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); 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; 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 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, or C3. The anatomical organization when C4 conventional, or unconventional. Organization of PCR tissue in a few C4 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); when biochemically tested, XyMS+ (C3, or C4 NAD-ME or PCK), or XyMS– (NADP-ME). 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. PBS cells without a suberised lamella. 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.
Taxonomy. Panicoideae; Panicodae; Paniceae. Panics.
Distribution, ecology, phytogeography. About 370 species; 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.
Holarctic, Paleotropical, Neotropical, Australian, and Antarctic. Boreal, Tethyan, and Madrean. African, Madagascan, Indomalesian, Polynesian, and Neocaledonian. Euro-Siberian, Eastern Asian, 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 and Central Australian. New Zealand and Patagonian. European and Siberian. Canadian-Appalachian, Southern Atlantic North American, and Central Grasslands. Sahelo-Sudanian, Somalo-Ethiopian, South Tropical African, and Kalaharian. Tropical North and East Australian and Temperate and South-Eastern Australian.
Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia dolosa, ‘Uromyces’ setariae-italicae, and Puccinia esclavensis.
Economic importance. 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. bulbosum, 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).
References, etc. Morphological/taxonomic: Hitchcock and Chase 1910, 1915; Hsu 1965; Brown 1977; Zuloaga and Soderstrom 1985; Zuloaga 1987; Ellis 1988. Leaf anatomical: mainly Metcalfe 1960 and this project.
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. Consequent re-alignments of species might reduce the variability here attributed to Panicum. See W. V. Brown (1977) for discussion, and Zuloaga (1987) for a detailed treatment of the New World species. 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 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 cannot be effectively implemented until the generic circumscriptions have been clarified (cf. Webster 1987, Zuloaga 1987).
Illustrations. • General aspect. • Bulbous culm base. Panicum bulbosum. • Ligule. • Inflorescence. Panicum stapfianum. • Inflorescence (part). • Inflorescence, spikelet. • Spikelet, floret. • Spikelet, flower. • Inflorescence base (immature). • Inflorescence pulvinus. • Spikelets. • Spikelet. Panicum laevifolium. • Spikelet, with parts displayed. 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. • Leaf blade transverse section. Panicum bulbosum. • Leaf blade transverse section. Panicum pygmaeum. • Leaf blade transverse section. Panicum effusum. • Leaf blade transverse section. Panicum miliaceum. • Leaf blade transverse section. Panicum bulbosum. • Leaf blade transverse section, electron micrograph. Panicum effusum. C4 type NAD-ME. • Leaf blade transverse section, electron micrograph. Panicum maximum. C4 type PCK. • Seedling
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).
