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The grass genera of the world

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

Agrostis L.

From the Greek agrostis (a forage plant, a kind of grass), cf. agros (a field).

Bents, Blowngrasses.

Type species: Type: A. alba L.

Including Agraulus P. Beauv., Agrestis Bub., Anomalotis Steud., Bromidium Nees, Candollea Steud., Chaetotropis Kunth, Decandolea Batard, Didymochaeta Steud., Lachnagrostis Trin., Neoschischkinia Tsvelev, Notonema Raf., Pentatherum Nabelek, Podagrostis (Griseb.) Scribn., Senisetum Koidz., Trichodium Michaux, Vilfa Adans.

Excluding Linkagrostis (A. juressi)

Habit, vegetative morphology. Annual, or perennial; rhizomatous, or stoloniferous, or caespitose, or decumbent. Culms mostly (3–)5–100 cm high; herbaceous; branched above, or unbranched above. Culm nodes glabrous. Culm internodes hollow. Leaves mostly basal, or not basally aggregated; non-auriculate. Sheath margins free. Leaf blades linear; apically flat; narrow; 0.2–10 mm wide; usually flat, or rolled (convolute, or canaliculate); not pseudopetiolate; without cross venation; persistent; rolled in bud. Ligule an unfringed membrane; truncate, or not truncate; 1–6 mm long.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets; outbreeding; exposed-cleistogamous, or chasmogamous.

Inflorescence. Inflorescence paniculate; deciduous in its entirety (Lachnagrostis), or not deciduous; open, or contracted (e.g., Bromidium); when contracted, spicate, or more or less irregular (not usually ‘interrrupted’); with capillary branchlets, or without capillary branchlets. Primary inflorescence branches where known, inserted all around the main axis. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets 0.8–4 mm long; compressed laterally; disarticulating above the glumes. Rachilla prolonged beyond the uppermost female-fertile floret, or terminated by a female-fertile floret; hairy, or hairless; the rachilla extension when present, naked. Hairy callus present (the hairs less than 0.5 mm long), or absent. Callus hairs absent, or if present less than 0.5 mm long. Callus short (minute); blunt.

Glumes two; more or less equal; about equalling the spikelets to exceeding the spikelets (nearly always), or shorter than the spikelets (very rarely); long relative to the adjacent lemmas; not ventricose; pointed; awnless; carinate, or non-carinate; similar (usually narrow, membranous). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only; without proximal incomplete florets.

Female-fertile florets 1(–2). Lemmas not saccate; less firm than the glumes (thinly membranous to hyaline); not becoming indurated; entire to incised (usually truncate or emarginate, sometimes toothed via excurrent veins); awnless, or mucronate, or awned. Awns when present, 1, or 3 (Bromidium), or 5 (rarely); median, or median and lateral (by extension of the lateral veins); the median different in form from the laterals (when laterals present); dorsal; from well down the back; geniculate; much shorter than the body of the lemma to about as long as the body of the lemma, or much longer than the body of the lemma (rarely); entered by one vein. The lateral awns (when present) shorter than the median to exceeding the median. Lemmas hairy, or hairless; non-carinate; without a germination flap; 3–5 nerved. Palea nearly always present; relatively long, or conspicuous but relatively short, or very reduced; entire, or apically notched; not indurated (hyaline or membranous); nerveless, or 2-nerved; 2-keeled, or keel-less. Lodicules present; 2; free; membranous; glabrous; not toothed; not or scarcely vascularized. Stamens 3. Anthers 0.3–2 mm long; not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small; longitudinally grooved, or not grooved (rarely); compressed dorsiventrally. Hilum short. Embryo small; not waisted. Endosperm liquid in the mature fruit, or hard; with lipid; containing compound starch grains. Embryo with an epiblast; without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins meeting.

Seedling with a short mesocotyl, or with a long mesocotyl; with a loose coleoptile, or with a tight coleoptile. First seedling leaf with a well-developed lamina. The lamina broad, or narrow; erect; 3–5 veined.

Ovule, embryology. Micropyle oblique. Outer integument extensive, being absent only from the micropylar region; two cells thick at the micropylar margin. Inner integument continuous, the micropyle constricted; 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. Mid-intercostal long-cells fusiform; having straight or only gently undulating walls. Microhairs absent. Stomata common; 37–39 microns long (in A. avenacea). Subsidiaries low dome-shaped, or parallel-sided. Guard-cells overlapped by the interstomatals. Intercostal short-cells absent or very rare. Costal short-cells neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies horizontally-elongated crenate/sinuous, or tall-and-narrow.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs, or ‘nodular’ in section; with the ribs more or less constant in size. Midrib conspicuous, or not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups, or not present in discrete, regular adaxial groups; when well defined, in simple fans (or the groups of fairly uniform cells). Many of the smallest vascular bundles unaccompanied by sclerenchyma, or all the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present, or absent; nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Culm anatomy. Culm internode bundles in one or two rings.

Phytochemistry. Tissues of the culm bases with little or no starch. Leaves without flavonoid sulphates (1 species).

Special diagnostic feature. Lemmas without the characteristic Corynephorus awn.

Cytology. Chromosome base number, x = 7. 2n = 14, 16, 21, 28, 30, 32, 35, 42, 44, 46, and 56 (and aneuploids). 2, 3, 4, 5, 6, 7, and 8 ploid (and aneuploids). Chromosomes ‘large’. Haploid nuclear DNA content 1.5 and 1.8 pg (2 species). Mean diploid 2c DNA value 6.9 pg (1 species).

Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Aveneae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Agrostidinae. About 220 species.

Distribution, phytogeography, ecology. Worldwide-temperate.

Commonly adventive. Helophytic, or mesophytic, or xerophytic (rarely); shade species and species of open habitats; nearly always glycophytic. Grassland, light woodland, rarely sand dunes.

Economic aspects. Significant weed species: A. canina, A. castellana, A. gigantea, A. stolonifera, A. tenuis. Cultivated fodder: A. palustris, A. tenuis (only for poor, acid soils), etc. Important native pasture species: A. exarata, A. oregonensis, A. tenuis, A. variabilis etc. Lawns and/or playing fields: A. canina, A. stolonifera, A. tenuis etc.

Hybrids. Intergeneric hybrids with PolypogonAgropogon P. Fourn.), Calamagrostis.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia graminis, Puccinia coronata, Puccinia striiformis, Puccinia pygmaea, Puccinia brachypodii, Puccinia praegracilis, Puccinia poarum, Puccinia recondita, ‘Uromycesfragilipes, and ‘Uromycesdactylidis. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae — Entyloma, Tilletia, and Urocystis. Ustilaginaceae — Sphacelotheca.

References, etc. Morphological/taxonomic: Vickery 1941; Bjorkman 1960; Nicora 1962. Leaf anatomical: Metcalfe 1960; studied by us - A. aemula R. Br., A. australiensis Mez, A. avenacea Gmelin, A. billardieri R.Br., A. tenuis Sibth. (= A. capillaris L.).

Illustrations. • A. canina, general aspect: Eng. Bot. (1872). • A. curtisii (as setacea), general aspect: Eng. Bot. (1872). • A. tenuis (as vulgaris), general aspect: Eng. Bot. (1872). • xAgropogon littoralis (A. stolonifera x Polypogon monspeliensis, as P. littoralis): Eng. Bot. (1872). • A. (Lachnagrostis) aequata and A. venusta: Hooker, Fl. Tasmaniae (1860). • A. (Lachnagrostis) rudis (as A. scabra): Hooker, Fl. Tasmaniae (1860). • A. avenacea, = Lachnagrostis rudis: Gardner, 1952. • A. eriantha: Gibbs Russell et al., 1990. • A. parviflora: Hooker, Fl. Tasmaniae (1860). • Spikelets of A. parviflora. • Agrostis magellanica: Hooker, Fl. Antarctica (1844). • Spikelets. • Spikelets. • Spikelet. • Spikelet. • Abaxial epidermis of leaf blade. • Pollen antigens: Watson and Knox (1976). • Pollen antigens: cross-reactions against anti-Lolium serum. • Pollen antigens: cross-reactions against anti-Lolium serum. • Heat stable pollen antigens (allergens): cross-reactions against anti-Lolium serum. • Pollen antigens: cross-reactions against anti-Cynodon serum

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: 11th December 2017.’.