| # The grass genera of the world |

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

### Deyeuxia Clarion ex P. Beauv.

After Nicolas Deyeux (1753–1837) Professor of Pharmacy Medicine, Paris.

Bent grasses.

~ Calamagrostis. See also Agrostis, Dichelachne

Type species: Type: D. montana (Gaudin) P.Beauv., nom. illeg..

Including Sclerodeyeuxia (Stapf) Pilger

Excluding D. uncinioides = Ancistragrostis, Aniselytron, Stilpnophleum

Habit, vegetative morphology. Perennial; caespitose. Culms herbaceous; unbranched above. Culm nodes glabrous. Culm internodes hollow. Leaves mostly basal, or not basally aggregated; non-auriculate. Leaf blades apically cucullate; narrow; not pseudopetiolate; without cross venation; persistent. Ligule an unfringed membrane; truncate; 0.5–2 mm long.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality. Plants inbreeding.

Inflorescence. Inflorescence paniculate; open, or contracted; when contracted, spicate to more or less irregular; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets 1–8 mm long; compressed laterally; disarticulating above the glumes. Rachilla prolonged beyond the uppermost female-fertile floret, or terminated by a female-fertile floret (rarely); hairy, or hairless; the rachilla extension when present, naked. Hairy callus present (the hairs sometimes 0.5 mm or more long, but shorter than the lemma), or absent.

Glumes two; very unequal, or more or less equal; about equalling the spikelets to exceeding the spikelets; long relative to the adjacent lemmas (the lemma usually at least 3/4 as long, by contrast with Calamagrostis, but only about half as long in D. drummondii); pointed, or not pointed; awnless; carinate; similar. Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only.

Female-fertile florets 1(–2). Lemmas decidedly firmer than the glumes (the main, equivocal distinction from Agrostis); not becoming indurated; incised; usually minutely 2–4 lobed; not deeply cleft (toothed); nearly always awned (rarely only mucronate). Awns when present, 1; dorsal; from near the top, or from well down the back; non-geniculate, or 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; entered by one vein; deciduous, or persistent. Lemmas hairless; non-carinate; 4–5 nerved. Palea present; relatively long, or conspicuous but relatively short, or very reduced; 2-nerved; 2-keeled. Lodicules present; 2; free; membranous; glabrous; not toothed. Stamens 3. Anthers 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; with hairs confined to a terminal tuft. Hilum short. Embryo small.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally (elongated); differing markedly in wall thickness costally and intercostally (the costals thicker walled). Mid-intercostal long-cells rectangular to fusiform; having straight or only gently undulating walls. Microhairs absent. Stomata common. Subsidiaries low dome-shaped, or parallel-sided. Guard-cells overlapped by the interstomatals. Intercostal short-cells absent or very rare; not paired; not silicified. Costal short-cells conspicuously in long rows, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies horizontally-elongated crenate/sinuous, or horizontally-elongated smooth, or rounded.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. 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 not present in discrete, regular adaxial groups (irregularly grouped in the furrows, of small cells - cf. Ammophila). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 7. 2n = 28.

Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Aveneae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Agrostidinae. 42 species.

Distribution, phytogeography, ecology. Temperate.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia graminis, Puccinia hordei, and Puccinia recondita. Smuts from Ustilaginaceae. Ustilaginaceae — Ustilago.

References, etc. Morphological/taxonomic: Vickery 1940. Leaf anatomical: Metcalfe 1960; studied by us - D. affinis M. Gray, D. crassiuscula Vickery, D. quadriseta (Labill.) Benth.

Illustrations. • Deyeuxia monticola (as Agrostis): Hooker, Fl. Tasmaniae (1860). • Deyeuxia contracta (as Agrostis): Hooker, Fl. Tasmaniae (1860). • Deyeuxia drummondii, inaequalis, quadriseta: spikelets and lemmas, Gardner, 1952. • Inflorescence detail of Deyeuxia angustifolia. • Deyeuxia quadriseta, abaxial epidermis of leaf blade: this project. • Deyeuxia quadriseta, abaxial epidermis of leaf blade - silica bodies: 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: 15th June 2025. delta-intkey.com’.

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