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The grass genera of the world

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

Deschampsia P. Beauv.

After Dr. Deschamps of Saint-Omer.

Type species: Type: D. caespitosa P.Beauv.

Including Airidium Steud., Aristavena Albers & Butzin, Avenella Parl., Campella Link, Czerniaevia Ledeb., Erioblastus Honda, Homoiachne Pilger, Lerchenfeldia Schur, Podinapus Dulac

Excluding Periballia, Vahlodea

Habit, vegetative morphology. Annual, or perennial; rhizomatous, or stoloniferous, or caespitose, or decumbent (but usually caespitose). Culms 8–200 cm high; herbaceous; unbranched above. Culm nodes glabrous. Culm internodes hollow. Young shoots intravaginal. Leaves mostly basal; non-auriculate. Leaf blades linear; apically cucullate (at least in D. caespitosa); narrow; 0.3–6 mm wide; setaceous, or not setaceous; flat, or folded, or rolled (convolute); not pseudopetiolate; without cross venation; persistent; rolled in bud, or once-folded in bud. Ligule present; an unfringed membrane; not truncate; 3–15 mm long.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets; outbreeding and inbreeding; exposed-cleistogamous, or chasmogamous. Viviparous (sometimes), or not viviparous.

Inflorescence. Inflorescence paniculate; usually open; with capillary branchlets, or without capillary branchlets. Primary inflorescence branches borne distichously. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets 3–9 mm long (small, delicate); compressed laterally; disarticulating above the glumes; with distinctly elongated rachilla internodes between the florets (the lower floret sessile). Rachilla prolonged beyond the uppermost female-fertile floret (the terminal extension well developed); hairy (except D. chapmanii); the rachilla extension with incomplete florets, or naked (well developed beyond the uppermost floret). Hairy callus present. Callus short; blunt.

Glumes two; very unequal (rarely), or more or less equal; shorter than the spikelets to exceeding the spikelets; long relative to the adjacent lemmas; pointed; awnless; carinate, or non-carinate; similar (subscarious to membranous, with thin margins). Lower glume 1 nerved, or 3 nerved. Upper glume 3 nerved, or 5 nerved. Spikelets with female-fertile florets only (usually), or with incomplete florets. The incomplete florets when present, distal to the female-fertile florets. The distal incomplete florets when present, 1. Spikelets without proximal incomplete florets.

Female-fertile florets (1–)2(–3). Lemmas similar in texture to the glumes to decidedly firmer than the glumes (hyaline to cartilaginous); not becoming indurated; entire, or incised (2-lobed, 4-toothed or truncate); not deeply cleft; awned (usually), or awnless to mucronate (D. tenella and New Zealand relatives, distinguished from Poa by their denticulate lemma tip). Awns 1; median; dorsal; from well down the back (mostly from the base or lower half, a few from above the middle); slender, weakly geniculate, or non-geniculate; hairless (glabrous to scabridulous); much shorter than the body of the lemma to much longer than the body of the lemma; entered by one vein. Lemmas hairy (rarely), or hairless; non-carinate (rounded on the back); 4–7 nerved. Palea present; relatively long; tightly clasped by the lemma; awnless, without apical setae; not indurated (membranous); 2-nerved; 2-keeled. Lodicules present; 2; joined, or free; membranous; glabrous; toothed, or not toothed; not or scarcely vascularized. Stamens 3. Anthers 0.3–2.5 mm long; not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small; longitudinally grooved; compressed dorsiventrally, or not noticeably compressed. Hilum short. Pericarp thin (shining). Embryo large (rarely), or small; not waisted. Endosperm 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 long mesocotyl; with a loose coleoptile, or with a tight coleoptile. First seedling leaf with a well-developed lamina. The lamina narrow; 3 veined.

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 (fairly thick walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs absent. Stomata common, or absent or very rare; 36–39 microns long. Subsidiaries parallel-sided. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs, or not paired; when paired silicified. Costal short-cells predominantly paired. Costal silica bodies horizontally-elongated crenate/sinuous, or horizontally-elongated smooth, or rounded; sharp-pointed (rarely), or not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade; traversed by columns of colourless mesophyll cells, or not traversed by colourless columns. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups, or not present in discrete, regular adaxial groups; when clearly grouped, in simple fans, or associated with colourless mesophyll cells to form deeply-penetrating fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent. Sclerenchyma not all bundle-associated. The ‘extra’ sclerenchyma in abaxial groups (but sometimes forming an almost continuous layer); abaxial-hypodermal, the groups isolated (opposite the bulliforms), or abaxial-hypodermal, the groups continuous with colourless columns.

Phytochemistry. Leaves without flavonoid sulphates (3 species).

Special diagnostic feature. Lemmas without the characteristic Corynephorus awn. Female-fertile lemma not as in Lombardochloa (q.v.).

Cytology. Chromosome base number, x = 7 and 13. 2n = 14, 24, 26, 28, 32, 42, 52, and 56 (and 26+B). 2, 4, 6, and 8 ploid (and aneuploids: some complexes with n = 13, 14). Chromosomes ‘large’. Haploid nuclear DNA content 3.1–4.5 pg (3 species). Mean diploid 2c DNA value 10 pg (D. antarctica).

Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Aveneae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Airinae (Avenella only), or Holcinae. 40 species.

Distribution, phytogeography, ecology. North and South temperate, high altitude tropics.

Commonly adventive. Helophytic, or mesophytic; shade species and species of open habitats. Meadows, upland grasslands and woods.

Economic aspects. Significant weed species: D. caespitosa, D. flexuosa. Important native pasture species: D. flexuosa.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia graminis, Puccinia coronata, Puccinia pygmaea, Puccinia praegracilis, Puccinia hordei, Puccinia recondita, and ‘Uromycesfragilipes. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae — Entyloma and Tilletia. Ustilaginaceae — Ustilago.

References, etc. Morphological/taxonomic: Koch 1979. Leaf anatomical: Metcalfe 1960; this project.

Illustrations. • D. cespitosa (as Aira): Eng. Bot. (1872). • cf. D. cespitosa ssp. alpina: Eng. Bot. (1872). • D. cespitosa, general aspect, spikelet, floret details. • D. flexuosa (as Aira), general aspect: Eng. Bot. 1872). • D. antarctica (as Aira): Hooker, Fl. Antarctica (1844). • D. atropurpurea (as Aira): Hooker, Fl. Antarctica (1844). • D. kingii (as Aira):: Hooker, Fl. Antarctica (1844). • D. chapmanii (as Catabrosa): Hooker, Fl. Antarctica (1844). • cf.bD. setacea (as Aira uliginosa): Eng. Bot. (1872). • D. caespitosa, abaxial epidermis of leaf blade: this project. • D. caespitosa, detsils of leaf blade abaxial epidermis: this project. • D. caespitosa, detsils of leaf blade abaxial epidermis: this project. • D. caespitosa, leaf blade TS: this project

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.’.