The grass genera of the world
Including Boriskerella Terekhov, Erochloe Raf., Erosion Lunell, Exagrostis Steud., Kalinia (E. Fourn.) H.L. Bell & Columbus, Macroblepharus Philippi, Psilantha (K. Koch) Tzvelev, Roshevitzia Tsvelev, Triphlebia Stapf, Vilfagrostis Doell
Excluding Acamptoclados, Cladoraphis, Diandrochloa, Neeragrostis, Stiburus, Thellungia
Habit, vegetative morphology. Annual, or perennial; caespitose (sometimes shrubby), or decumbent, or stoloniferous (rarely - e.g. E. hypnoides, E. barbinodis). Culms 10–300 cm high; herbaceous (usually), or woody and persistent (occasionally); amply to sparsely branched above, or unbranched above (commonly). The branching suffrutescent (e.g., E. mahrana), or fastigiate (e.g., E. fastigiata), or simple (mostly). Culms tuberous (rarely), or not tuberous; 1–5(–20) noded. Culm nodes nearly always glabrous, or hairy (very rarely, e.g. E. annulata, E. kennedyae). Culm internodes solid, or hollow. Plants without multicellular glands, or with multicellular glands (commonly, on various organs: buttonlike, elevated pitted glands mostly on leaf blades (e.g. E. cilianensis), crateriform glands (e.g. E. annulata), spot- or band-shaped glands often beneath nodes (e.g. E. trichophora), gland-based macrohairs common on leaf sheaths, blades or collars (e.g. E. trichocolea)). Leaves mostly basal, or not basally aggregated; auriculate (rarely), or non-auriculate (mostly). Sheath margins free. The sheaths keeled or not, glabrous or hairy and glandular. Leaf blades linear; broad to narrow (mostly narrow); flat, or folded, or rolled; without abaxial multicellular glands, or exhibiting multicellular glands abaxially (sometimes). The abaxial leaf blade glands on the blade margins, or costal. Leaf blades not pseudopetiolate; without cross venation; disarticulating from the sheaths (rarely, e.g. E. australasica), or persistent (usually); rolled in bud. Ligule present; a fringe of hairs (perhaps always, with Diandrochloa etc. excluded).
Reproductive organization. Plants bisexual, all with bisexual spikelets (with the exception of E. contrerasii Pohl - see Neeragrostis); with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant (occasionally), or all alike in sexuality (usually); sometimes hermaphrodite and male-only (e.g. E. superba, with reduced spikelets towards the extremities of the panicle). Plants outbreeding and inbreeding; exposed-cleistogamous, or chasmogamous; with hidden cleistogenes (rarely, e.g. E. scaligera, E. riobrancensis), or without hidden cleistogenes. The hidden cleistogenes when present, in the leaf sheaths. Apomictic, or reproducing sexually. Viviparous (sometimes), or not viviparous.
Inflorescence. Inflorescence few spikeleted, or many spikeleted; a false spike, with spikelets on contracted axes (occasionally, e.g. E. chapelieri)), or paniculate (mostly a decompound panicle, often with multicellular glands, characteristically scented); deciduous in its entirety (rarely, e.g. E. curtipedicellata), or not deciduous; open, or contracted; with conspicuously divaricate branchlets, or without conspicuously divaricate branchlets; with capillary branchlets, or without capillary branchlets (mostly). Inflorescence with axes ending in spikelets (nearly always), or axes not ending in spikelets (ending in bristles in no more than two or three species, e.g. E. canescens, E. hispida). Rachides neither flattened nor hollowed, not winged. Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; subsessile, or pedicellate.
Female-fertile spikelets. Spikelets 1–6.5–25(–40) mm long (and 0.5–3–8 mm wide, often lead coloured or purple tinged); compressed laterally (usually strongly so, but sometimes subterete in Section Cylindrostachya); disarticulating above the glumes (usually), or falling with the glumes (e.g. E. superba); not disarticulating between the florets (commonly, the paleas persistent), or disarticulating between the florets; with conventional internode spacings. Rachilla prolonged beyond the uppermost female-fertile floret; hairy (occasionally), or hairless (usually); the rachilla extension with incomplete florets (mostly), or naked (sometimes). Hairy callus absent. Callus absent (usually), or short; when present, blunt.
Glumes two (persistent most frequently in subgenus Caesia, deciduous most frequently in subgenus Eragrostis); very unequal to more or less equal; shorter than the spikelets; shorter than the adjacent lemmas; free; hairless; glabrous, or scabrous (on the veins); pointed (mostly), or not pointed (occasionally blunt); awnless; carinate (mostly), or non-carinate (a few); similar (mostly, membranous), or very dissimilar (E. stenostachya). Lower glume shorter than the lowest lemma to about equalling the lowest lemma; 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets (when present) nearly always distal to the female-fertile florets (a very few species with 1–3 incomplete lower florets). The distal incomplete florets 1–2(–3); merely underdeveloped (mostly with reduced palea and 1–2–3 veined lemma); awnless. Spikelets nearly always without proximal incomplete florets.
Female-fertile florets (2–)3–10–50(–80) (or more, the highest counts representing E. cilianensis var. thyrsiflora). Lemmas similar in texture to the glumes to decidedly firmer than the glumes (narrow, membranous to papery); not becoming indurated; entire, or incised; when incised, not deeply cleft (emarginate); awnless, or mucronate (very rarely almost awned, e.g. E. walteri); hairless (usually glabrous); glabrous, or scabrous; carinate (mostly), or non-carinate. The keel when present, wingless. Lemmas without a germination flap; (1–)3(–5) nerved (1–3 in E. kennedyae, 3–5 in E. walteri); with the nerves non-confluent (the lateral veins more often conspicuous than inconspicuous, usually with only the midvein reaching the margin). Palea present (often persistent on the rachilla after the lemma and fruit have dropped); relatively long (usually, but shorter than the lemma), or conspicuous but relatively short; entire (mostly), or apically notched (then usually bifid, rarely trifid); awnless, without apical setae; thinner than the lemma (membranous/hyaline); not indurated; 2-nerved; 2-keeled. Palea keels winged (rarely), or wingless; hairy (usually), or glabrous to scabrous. Lodicules present (usually), or absent; when present, 2; free; fleshy; glabrous. Stamens (2–)3 (mostly 3, but sometimes 2–3 or 2 (E. ciliaris)). Anthers (0.1–)0.2–0.6–1.8(–2.5) mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white, or red pigmented.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small (0.4–0.8–2.4 mm long); ellipsoid, or subglobose (or obovate); not grooved (mostly), or longitudinally grooved; compressed laterally (commonly, e.g. E. pilgerana), or compressed dorsiventrally (rarely), or not noticeably compressed (mostly), or trigonous (rarely); scabrous; smooth, or sculptured (sometimes finely striate or reticulate). Hilum short. Pericarp fused (usually), or loosely adherent (rather readily detachable in some species), or free (e.g. in E. megalosperma, E. stapfiana). Embryo large (0.3–0.5–0.7 times the length of the caryopsis); waisted (usually), or not waisted. Endosperm hard; without lipid; containing compound starch grains. Embryo with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.
Seedling with a long mesocotyl; with a loose coleoptile. First seedling leaf with a well-developed lamina. The lamina broad; curved; 3–5 veined.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent (nearly always), or present (E. obtusiflora). Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls (nearly always), or having straight or only gently undulating walls (rarely). Microhairs present; elongated; clearly two-celled; panicoid-type (subgenus Caesia), or chloridoid-type (subgenus Eragrostis, or some species with more or less intermediate forms), or Enneapogon-type (known only in E. annulata). Microhair apical cell wall thinner than that of the basal cell and often collapsed (subgenus Caesia), or thinner than that of the basal cell but not tending to collapse (few), or of similar thickness/rigidity to that of the basal cell (subgenus Eragrostis). Microhairs without partitioning membranes (E. cilianensis, E. parviflora, E. elongata, despite the first two being chloridoid-type); (30–)33–75(–156) microns long; (6–)7.5–11.5–15(–22) microns wide at the septum. Microhair total length/width at septum 2.75–12.7. Microhair apical cells (10–)12–41(–48) microns long. Microhair apical cell/total length ratio 0.3–0.61. Stomata common; (16.8–)19–36(–45) microns long. Subsidiaries non-papillate; low dome-shaped (usually), or triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs, or not paired (solitary); silicified (when paired), or not silicified. Intercostal silica bodies absent, or imperfectly developed, or present and perfectly developed; when present, rounded, or crescentic, or tall-and-narrow (most frequently), or saddle shaped. Intercostal macrohairs sometimes present, often associated with rosettes of specialized cells. Marginal and/or costal prickles often present, intercostal prickles sometimes present, these sometimes paired with short-cells. Costal short-cells conspicuously in long rows, or predominantly paired, or neither distinctly grouped into long rows nor predominantly paired (not infrequently). Costal silica bodies present and well developed; present throughout the costal zones (subgenus Caesia), or confined to the central file(s) of the costal zones (rare), or present in alternate cell files of the costal zones (subgenus Eragrostis); saddle shaped (commonly), or rounded, or tall-and-narrow (rarely), or crescentic, or panicoid-type; sometimes cross shaped, or nodular.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4 (with the former startling exception, Eragrostis walteri, referred eldewhere: see Ingram et al., Ann. Bot. Nov. 23, 2010); biochemical type NADME (in all 14 species typed, although some exhibit PCK-like leaf blade anatomy); XyMS+. PCR sheath outlines uneven, or even, or uneven to even. PCR sheath extensions present (subgenus Caesia), or absent (subgenus Eragrostis). Maximum number of extension cells 1–3–7. PCR cells with a suberised lamella, or without a suberised lamella. PCR cell chloroplasts ovoid, or elongated; with well developed grana; centrifugal/peripheral, or centripetal, or centrifugal/peripheral to centripetal. Mesophyll with radiate chlorenchyma, or with non-radiate chlorenchyma; without adaxial palisade; traversed by columns of colourless mesophyll cells (rarely), or not traversed by colourless columns. Leaf blade with distinct, prominent adaxial ribs (commonly), or nodular in section (usually), or adaxially flat (E. chapelieri); when ribbed, with the ribs more or less constant in size (but larger above the primary bundles), or with the ribs very irregular in sizes (rarely). Midrib conspicuous, or not readily distinguishable (mostly); with one bundle only, or having a conventional arc of bundles (rarely). Bulliforms present in discrete, regular adaxial groups (nearly always), or not present in discrete, regular adaxial groups (E. pergracilis, no bulliforms in E. plana); associated with colourless mesophyll cells to form deeply-penetrating fans (mostly), or in simple fans and associated with colourless mesophyll cells to form deeply-penetrating fans (these sometimes linked to traversing columns of colourless cells). Usually all the vascular bundles accompanied by sclerenchyma, or many of the smallest vascular bundles unaccompanied by sclerenchyma (not uncommonly, especially towards the blade margins). Combined sclerenchyma girders present; forming figures. Sclerenchyma all associated with vascular bundles. The lamina margins without fibres, or with fibres.
Culm anatomy. Culm internode bundles in one or two rings.
Phytochemistry. Tissues of the culm bases with abundant starch. Leaves containing flavonoid sulphates (E. horizontalis), or without flavonoid sulphates (4 species). Leaf blade chlorophyll a:b ratio 3.39–4.48.
Cytology. Chromosome base number, x = 10. 2n = 20, 40, 50, 60, 80, 100, and 108. 2, 4, 5, 6, 8, and 10 ploid. Chromosomes small. Haploid nuclear DNA content 0.32 pg (1 species, 4x). Nucleoli persistent.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Eragrostideae; Eragrostidinae. 350 species.
Distribution, phytogeography, ecology. Cosmopolitan, mostly subtropical.
Commonly adventive. Helophytic (rarely), or mesophytic, or xerophytic; mostly species of open habitats; halophytic, or glycophytic. Often on poor or sandy soils or disturbed ground.
Economic aspects. Significant weed species: E. amabilis, E. aspera, E. aethiopica, E. atrovirens, E. barrelieri, E. cilianensis, E. curvula, E. diffusa, E. diarrhena, E. ferruginea, E. japonica, E. malayana, E. megastachya, E. mexicana, E. minor, E. multicaulis, E. neomexicana, E. pectinacea, E. pilosa, E. superba, E. tenella, E. tenuifolia, E. tremula, E. unioloides, E. virescens, E. viscosa, E. zeylanica. Cultivated fodder: E. tef; E. curvula and E. superba drought resistant, used for reseeding denuded land. Important native pasture species: mostly more or less unpalatable, but a few useful - e.g. E. capensis, E. cilianensis, E. ciliaris, E. curvula, E. patens, E. pilosa, E. rigidior, E. superba. Grain crop species: E. tef (Teff) a staple cereal in Ethiopia, potentially of wide interest.
Rusts and smuts. Rusts Physopella and Puccinia. Taxonomically wide-ranging species: Uromyces eragrostidis. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae Tilletia. Ustilaginaceae Sorosporium, Sphacelotheca, Tolyposporella, and Ustilago.
References, etc. Morphological/taxonomic: Koch 1978; Van den Borre and Watson 1994. Leaf anatomical: Metcalfe 1960; Prendergast et al. 1986; Van den Borre and Watson 1994; and this project.
Illustrations. • General aspect (E. curvula): Gibbs Russell et al., 1990. • General aspect (E. pallens): Gibbs Russell et al., 1990. • General aspect (E.rigidior): Gibbs Russell et al., 1990. • E.curvula, E. leptocarpa, E. parviflora, E. tenellula: Gardner, 1952. • E. cilianensis, E. speciosa: Gardner, 1952. • E. eriopoda, E. setifolia, E. xerophila: Gardner, 1952. • E. falcata, E. desertorum, E. lacunaria, E. lanipes: Gardner, 1952. • Spikelet of E. cilianensis. • Spikelet of E. parviflora. • Spikelet dehiscing (E. cumingii). • E. parviflora, old inflorescence with persistent rachillas and paleas: this project. Rachillas and paleas persisting after the rest of the spikelets have fallen. • E. benthamii, leaf blade TS: this project. • E. elongata, leaf blade T.S. with details of PCR sheaths: this project. Eragrostis elongata. PCR sheath outlines ‘uneven’, chloroplasts centrifugal. • E. parviflora, leaf blade T.S. showing PCR sheath details: original. Eragrostis parviflora. PCR sheath cell chloroplasts mostly centripetal. • ‘Chloridoid-type’ microhairs of E. parviflora and E. cilianensis: longitudinal EM sections (Amarasinghe). • ‘Panicoid-type’ microhairs of E. elongata and Panicum virgatum: longitudinal EM sections (Amarasinghe)
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: 13th November 2017. delta-intkey.com/grass’.