| # The grass genera of the world |

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

### Hordeum L.

Hordeum, the ancient Latin name for the barley.

Barley, Barley grasses.

Including Critesion Raf., Critho Meyer, Zeocrithon P. Beauv., Zeocriton Wolf

Habit, vegetative morphology. Annual, or perennial; caespitose (or the culms solitary). Culms 5–130 cm high; herbaceous; unbranched above; tuberous, or not tuberous. Culm nodes glabrous. Culm internodes hollow. Leaves not basally aggregated; auriculate, or non-auriculate. Leaf blades linear; apically flat; broad (rarely), or narrow; 1.5–15 mm wide; not setaceous; usually flat, or rolled (convolute); without cross venation; persistent; rolled in bud. Ligule an unfringed membrane; truncate; 0.5–1 mm long.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and male-only, or hermaphrodite and sterile (the lateral spikelets sterile in Critesion, male in Hordeum sensu stricto). Plants outbreeding and inbreeding; exposed-cleistogamous, or chasmogamous.

Inflorescence. Inflorescence a false spike, with spikelets on contracted axes (the spikelets in triads); contracted. Inflorescence with axes ending in spikelets, or axes not ending in spikelets (the main axis lacking a terminal spikelet). Rachides hollowed. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes disarticulating, or persistent (in cultivated forms); falling entire (the triplets shed, in Hordeum sensu stricto), or disarticulating at the joints (the main axis fragile, e.g. in Critesion). Spikelets in triplets (the triplets shed together); not secund; distichous, or not two-ranked (in 2–6 rows); consistently in ‘long-and-short’ combinations, or not in distinct ‘long-and-short’ combinations (rarely, the laterals also sessile); usually in pedicellate/sessile combinations (the central spikelet of each triplet sessile, the laterals pedicellate). The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets hermaphrodite, or male-only, or sterile (in Critesion).

Female-sterile spikelets. The lateral spikelets usually smaller, when sterile sometimes reduced to clusters of awns.

Female-fertile spikelets. Spikelets compressed laterally to compressed dorsiventrally; falling with the glumes (in the deciduous triplets), or not disarticulating (in cultivated forms). Rachilla usually prolonged beyond the uppermost female-fertile floret (at least in the central spikelets of the triplets); hairy, or hairless; the rachilla extension naked.

Glumes two (unless the side by side pair in such forms represent a split G1, with G2 lacking (Butzin 1965)); more or less equal; free; displaced (side by side); subulate to not subulate; awned; similar (persistent, awn- or bristle-like above). Lower glume 1(–3) nerved. Upper glume 1(–3) nerved. Spikelets with female-fertile florets only.

Female-fertile florets 1. Lemmas acuminate to an awn or awn point; similar in texture to the glumes (leathery); not becoming indurated; entire, or incised; when incised, 2 lobed, or 3 lobed; awned (nearly always), or mucronate (in some South American species). Awns 1; median; apical; non-geniculate; much shorter than the body of the lemma to much longer than the body of the lemma; entered by several veins. Lemmas hairless; non-carinate; 5 nerved. Palea present; relatively long; entire, or apically notched, or deeply bifid; awnless, without apical setae; 2-nerved; 2-keeled. Lodicules present; free; membranous; ciliate; toothed, or not toothed. Stamens 3. Anthers 0.2–5 mm long; not penicillate. Ovary apically hairy. Styles free to their bases. Stigmas 2; white.

Fruit, embryo and seedling. Fruit adhering to lemma and/or palea, or free from both lemma and palea; small to large; longitudinally grooved; compressed dorsiventrally; with hairs confined to a terminal tuft. Hilum long-linear. Embryo small; not waisted. Endosperm hard; without lipid; containing only simple starch grains. Embryo with an epiblast; without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins meeting.

Seedling with a short mesocotyl; with a loose coleoptile, or with a tight coleoptile. First seedling leaf with a well-developed lamina. The lamina narrow; erect; 3–7 veined.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells the intercostals much larger; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls, or having straight or only gently undulating walls. Microhairs absent. Stomata common. Subsidiaries parallel-sided, or parallel-sided and dome-shaped. Guard-cells overlapped by the interstomatals. Intercostal short-cells common, or absent or very rare; when present, in cork/silica-cell pairs, or not paired (solitary); silicified. Intercostal silica bodies when present, rounded, or crescentic. Costal short-cells conspicuously in long rows, or predominantly paired, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies horizontally-elongated crenate/sinuous, or horizontally-elongated smooth, or rounded, or crescentic.

Transverse section of leaf blade, physiology. C3; XyMS+. PBS cells without a suberised lamella. Mesophyll with non-radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs, or ‘nodular’ in section, or adaxially flat; 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 (in the furrows); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’, or 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. Fructosans predominantly short-chain. Leaves without flavonoid sulphates (2 species).

Cytology. Chromosome base number, x = 7. 2n = 14, 28, and 42 (the polyploids supposedly only in ‘Critesion’). 2, 4, and 6 ploid. Haplomic genome content H (Critesion), or I (Hordeum sensu stricto). Chromosomes ‘large’. Haploid nuclear DNA content 5.4–5.6 pg (15 species, mean 5.5). Mean diploid 2c DNA value 11 pg (11 species, 10.8–11.1). Nucleoli disappearing before metaphase.

Classification. Watson & Dallwitz (1994): Pooideae; Triticodae; Triticeae. Soreng et al. (2015): Pooideae; Triticodae; Triticeae; Hordeinae. About 40 species.

Distribution, phytogeography, ecology. North temperate & South America.

Commonly adventive. Mesophytic, or xerophytic; species of open habitats; halophytic and glycophytic. Open weedy or sandy places, mostly in dry soils.

Economic aspects. Significant weed species: H. jubatum, H. leporinum, H. marinum, H. murinum (the fruiting inflorescence parts of these causing eye and other damage to livestock, and problems with wool). Grain crop species: H. vulgare (Barley); including (e.g.) H. distichon, H. aegiceras.

Hybrids. Intergeneric hybrids with Elytrigia (×Elytrordeum Hylander, ×Elyhordeum Zizan & Petrowa), Agropyron (×Agrohordeum A. Camus), Secale (×Hordale Ciferri & Giacom.), Sitanion (×Sitordeum Bowden), Triticum (×Tritordeum Aschers. & Graebn.).

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia graminis, Puccinia coronata, Puccinia striiformis, Puccinia montanensis, Puccinia hordei, Puccinia recondita, ‘Uromyces’ turcomanicum, ‘Uromyces’ fragilipes, and ‘Uromyces’ hordeinus. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae — Entyloma, Tilletia, and Urocystis. Ustilaginaceae — Ustilago.

References, etc. Morphological/taxonomic: Löve 1984. Leaf anatomical: Metcalfe 1960; studied by us - H. glaucum Steud., H. leporinum Link, H. vulgare L.

Illustrations. • Hordeum vulgare: Bor, Flora of Iraq (1968). • Hordeum vulgare, and H. distichon (as Zeocriton): P. Beauv. (1812). • Hordeum marinum (as H. maritimum), general aspect: Eng. Bot. (1872). • General aspect of Hordeum murinum: Gibbs Russell et al., 1990. • Hordeum murinum, general aspect: Eng. Bot. (1872). • Hordeum secalinum (as H. pratense), general aspect: Eng. Bot. (1872). • Triplet of spikelets (Hordeum bulbosum). • Lateral member of spikelet triplet (Hordeum bulbosum). • Grass pollen antigens: Watson and Knox (1976).

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’.

Contents