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Poaceae

THOMAS A. COPE


Herbarium, Royal Botanic Gardens, Kew.

  • Gramineae A. L. Jussieu

    Annual or perennial herbs, rarely shrubs or trees, sometimes with rhizomes or stolons; stems erect, ascending or creeping, usually branched at the base, in perennials with sterile shoots and flowering stems (culms) mixed, in annuals only the latter present; culms cylindrical, rarely flattened, jointed, usually hollow in the internodes, closed at the nodes; branches subtended by a leaf, and with a 2-keeled hyaline leaflet (prophyll) at the base. Leaves solitary at the nodes, sometimes crowded at the base of the stem, alternate and 2-rowed, consisting of sheath, ligule and blade; sheaths encircling the stem, with the margins free and overlapping or ± connate, frequently swollen at the base, the shoulders sometimes extended upwards into triangular auricles; ligule adaxial, placed at the junction of sheath and blade, membranous or reduced to a fringe of hairs, rarely absent (very rarely with a similar abaxial structure, the external ligule); blades usually long and narrow, rarely broad, flat or sometimes rolled or terete, parallel-nerved, rarely with transverse connections, usually passing gradually into the sheath, sometimes amplexicaul or with falcate auricles, rarely narrowed into a false petiole or articulated with the sheath. Inflorescences made up of spikelets arranged in a panicle, or in spikes or racemes, these either solitary, digitate or disposed along a central axis, usually terminal, sometimes (especially in Andropogoneae) numerous, each inflorescence being subtended by a bladeless sheath (spatheole) and the whole flowering branch system condensed into a leafy false panicle. Spikelets consisting of bracts distichously arranged along a slender axis (rhachilla); the 2 lower bracts (glumes) empty; the succeeding 1 to many bracts (lemmas) each enclosing a flower and opposed by a hyaline scale (palea), the whole (lemma, palea and flower) termed a floret; base of spikelet or floret sometimes with a horny prolongation downwards (callus); glumes or lemmas often bearing 1 or more stiff bristles (awns); this basic pattern of spikelet structure consistent throughout the family, though often much modified by reduction, suppression or elaboration of parts. Flowers usually bisexual, sometimes unisexual, small and inconspicuous; perianth represented by 2, rarely 3, minute hyaline or fleshy scales (lodicules); stamens hypogynous, 1-6, rarely more, usually 3, with delicate filaments and 2-thecous anthers opening by a longitudinal slit or rarely a terminal pore; ovary 1-locular, with 1 anatropous ovule often adnate to the adaxial side of the carpel; styles usually 2, rarely 1 or 3, generally with plumose stigmas. Fruit mostly a caryopsis with thin pericarp adnate to the seed, rarely with a free seed, still more rarely, a nut or berry; caryopsis commonly combined with various parts of the spikelet, or less often the inflorescence, to form a false fruit; seed with starchy endosperm, an embryo at the base of the abaxial face, and a point or line (hilum) on the base of adaxial face marking the connection between pericarp and seed.

    About 620 genera and 10,000 species in ± 60 tribes; throughout the world; 158 genera and 492 species in 26 tribes in Pakistan. Zea is not in the numbered sequence.

    The grasses form a natural and homogeneous family, remarkable both for the constancy of its basic theme and for the number of variations that have been derived from it. The division of the family into tribes was formerly based upon spikelet morphology, but now relies heavily upon cryptic characters whose significance is discussed by Bor, Grasses Burma Ceyl. Ind. Pak. (1960) and Jacques-Felix, Les Graminees d’Afrique tropicale (1962). Among the most important of these are characters derived from the anatomy of the plant, briefly summarised below in the subfamily descriptions, but described in detail by Metcalfe, Anatomy of the Monocotyledons I Gramineae (1960).

    It is not always easy to separate annuals from perennials, though the character is sometimes unavoidable in keys. The following characters should be looked for in perennials: sterile shoots mixed with the flowering culms; charred remnants of the previous year’s growth; dormant buds on the rootstock; perennating rhizomes.

    Acknowledgements: The author, editors and publisher are grateful to the Government of Iraq, the holder of the copyright, for kindly allowing the reproduction of 58 plates already published in the Flora of Iraq, Volume 9 and to the Director, Royal Botanic Gardens, Kew, for his good offices on their behalf in obtaining this concession. They are also grateful to the U.S. Department of Agriculture for financing the project under P.L. 480.


    KEY TO TRIBES

    1 Spikelets 1-many-flowered, breaking up at maturity above the ± persistent glumes, or if falling entire then not 2-flowered with the upper floret bisexual and the lower male or barren; spikelets usually laterally compressed or terete   (2)
    + Spikelets 2-flowered, falling entire at maturity, with the upper floret bisexual and the lower male or barren and in the latter case often much reduced; spikeletes usually dorsally compressed   (29)
           
    2 (1) Tall woody arborescent or shrubby bamboos; leaf-blades flat, lanceolate, many-nerved with transverse veins, usually with a petiole-like base and articulated with the sheath; lemmas several, 5-many-nerved, awnless; lodicules usually 3.   POACEAE Tribe BAMBUSEAE
    + Perennial or annual herbs with herbaceous culms; leaf-blades sessile and not articulated with the sheath   (3)
           
    3 (2) Inflorescence a spike with the spikelets sunk in cavities in the fragile rhachis; glumes inserted laterally, completely covering the cavity; mouth of leaf-sheath without auricles   Poaceae Tribe Hainardeae
    + Inflorescence not as above, if a spike with the spikelets sunk in cavities then either the lower glume absent and the upper minute (Psilurus) or mouth of leaf-sheath with auricles (Henrardia)   (4)
           
    4 (3) Ovary with a fleshy, hairy apical appendage, the styles arising from beneath it   (5)
    + Ovary sometimes hairy at the tip but without a fleshy hairy apical appendage; styles terminal   (7)
           
    5 (4) Inflorescence an open or contracted panicle   POACEAE Tribe BROMEAE
    + Inflorescence a spike or raceme, the spikelets placed broad-side to the rhachis, I-several at a node   (6)
           
    6 (5) Spikelets solitary at the nodes of the rhachis, borne upon a pedicel 1-3 mm long, several-flowered   POACEAE Tribe BRACHYPODIEAE
    + Spikelets 1-several at the nodes of the rhachis, quite sessile, or if on a short pedicel then either 1-flowered or borne in pairs at least in the middle part of the spike   POACEAE Tribe TRITICEAE
           
    7 (4) Lemmas deeply cleft into 9 lobes or awns   POACEAE Tribe PAPPOPHOREAE
    + Lemmas entire or bilobed, awnless or at most 3-awned   (8)
           
    8 (7) Spikelets containing 1 fertile floret (except Tetrapogon) with or without 1 or 2 male or barren florets below it or 1 or more above (if spikelets sunk in cavities in the spike-axis see 108. Psilurus)   (9)
    + Spikelets containing 2 or more fertile florets, rarely 1 but this succeeded by several sterile lemmas reduced to a clavate mass (Melica)   (20)
           
    9 (8) Glumes very minute or suppressed   (10)
    + Glumes usually well-developed, or at least the upper; palea usually 2-nerved and hyaline; stamens 3 or fewer   (11)
           
    10 (9) Inflorescence a panicle; spikelets 1-flowered or 3-flowered with the 2 lower florets reduced to glume-like lemmas; palea 3-nerved; stamens 6   POACEAE Tribe ORYZEAE
    + Inflorescence a single terminal 2-flowered spikelet exserted from a spathe-like sheath; lemmas fused into a tube; paleas 2-nerved, fused below along the back; stamens 3   Poaceae Tribe Lygeae
           
    11 (9) Spikelets falling entire at maturity, either singly or in clusters, from the persistent axis of spike-like panicles or racemes; lemma delicately 1-3-nerved (if spikelets falling entire with the pedicel or part of it from an open or contracted, lobed panicle, see XX Aveneae)   Poaceae Tribe Zoysieae
    + Spikelets breaking up at maturity above the persistent glumes   (12)
           
    12 (11) Inflorescence of racemes or spikes, these solitary, digitate or scattered along an axis, rarely a dense ovoid, spike like panicle (Fingerhuthia)   Poaceae Tribe Chlorideae
    + Inflorescence a panicle, either open or contracted and spike-like   (13)
           
    13 (12) Spikelets 1-flowered   (14)
    + Spikelets 2-3-flowered (the two lower florets may be reduced to minute chaffy scales at the base of the fertile lemma)   (18)
           
    14 (13) Lemmas bearing a 3-branched awn   POACEAE Tribe ARISTIDEAE
    + Lemmas with an unbranched awn or awnless   (15)
           
    15 (14) Lemmas indurated at maturity or if hyaline then bibbed with the lobes produced as 2 stout scabrid bristles   (16)
    + Lemmas hyaline or membranous at maturity, not bibbed with the lobes produced as stout scabrid bristles   (17)
           
    16 (15) Spikelets awned   POACEAE Tribe STIPEAE
    + Spikelets awnless   Poaceae Tribe Milieae
           
    17 (15) Lemmas usually awned; glumes longer and firmer than the hyaline lemma; grain with adherent pericarp   POACEAE Tribe AVENEAE
    + Lemmas usually awnless; glumes and lemmas similar in texture, the former often shorter; grain with loose pericarp (lemma long-awned and pericarp adherent in Muhlenbergia)   Poaceae Tribe Sporoboleae
           
    18 (13) Florets 2 per spikelet, the lower male or barren, the upper bisexual, rarely the rhachilla produced and bearing a third male or rudimentary floret   (19)
    + Florets 3 per spikelet, the fertile floret with 2 sterile florets below; rhachilla not produced   POACEAE Tribe AVENEAE
           
    19 (18) Spikelets 4-14 mm long   POACEAE Tribe ARUNDINELLEAE
    + Spikelets 1.2-1.8 mm long   POACEAE Tribe THYSANOLAENEAE
           
    20 (8) Tall reed-like grasses with large plumose panicles   Poaceae Tribe Arundineae
    + Slender grasses without large plumose panicles   (21)
           
    21 (20) Spikelets 2-flowered, both of the lemmas hardened or leathery; spikelets awnless   POACEAE Tribe ISACHNEAE
    + Spikelets nearly always 3- or more flowered; lemmas membranous or awned   (22)
           
    22 (21) Inflorescence made up of racemes, either solitary, digitate or scattered along an axis, sometimes in dense ovoid heads   (23)
    + Inflorescence an open to contracted panicle, if a simple spike then lemma 5- or more nerved   (24)
           
    23 (22) Lemma 1-3-nerved, if 5-nerved then the two lowermost lemmas empty and resembling the glumes (Tetrachne)   POACEAE Tribe ERAGROSTIDEAE
    + Lemma 9-11- nerved   Poaceae Tribe Aeluropodeae
           
    24 (22) Glumes shorter than the lowest lemma, with the upper florets distinctly exserted; lemmas awnless or with a straight awn from the entire or bilobed tip   (25)
    + Glumes longer than the lowest lemma, usually as long as the spikelet and enclosing the florets, rarely shorter but then the lemmas with a geniculate or dorsal awn; lemmas 5-many-nerved   (28)
           
    25 (24) Lemmas 1-3-nerved, if 5-nerved then plant producing cleistogamous spikelets (cleistogenes) form the lower sheaths (Kengia)   POACEAE Tribe ERAGROSTIDEAE
    + Lemmas 5-many-nerved, if 3-nerved then plant a tall, broad-leaved fescue (Festuca asthenica) or the lemma with a blunt, broadly hyaline tip   (26)
           
    26 (25) Sheaths open along the edges; all florets fertile or the upper gradually reduced, rarely the spikelets dimorphic (Lamarckia)   POACEAE Tribe POEAE
    + Sheaths tubular, fused along the margins   (27)
           
    27 (26) Only the lowest 1-3 florets fertile, the upper 2-3 clearly barren and often reduced to a clavate mass of sterile lemmas   POACEAE Tribe MELICEAE
    + All florets fertile or the upper gradually reduced; lemmas with distinctive parallel nerves   Poaceae Tribe Glycerieae
           
    28 (24) Lemmas awned from the back, rarely awnless; ligule membranous   POACEAE Tribe AVENEAE
    + Lemmas awned from the sinus of the prominently 2-lobed tip; ligule a ciliate fringe   Poaceae Tribe Arundineae
           
    29 (1) Spikelets solitary, rarely paired with the spikelets all alike; glumes usually membranous, the lower mostly smaller or sometimes suppressed; upper lemma papery to polished and stony, usually awnless   POACEAE Tribe PANICEAE
    + Spikelets typically paired with 1 sessile and the other pedicelled, those of each pair usually dissimilar (the pedicelled sometimes much reduced), rarely with the spikelets all alike; glumes as long as the spikelets and enclosing the florets, ± rigid and firmer than the hyaline or membranous lemmas; upper lemma often with a geniculate awn   POACEAE Tribe ANDROPOGONEAE

  • List of lower taxa


     

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