| # The grass genera of the world |

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

### Bromus L.

From the Greek bromos (oat), out of broma (food).

Type species: Type: B. secalinus L.

Including Aechmorpha Steud., Anisantha Koch, Avenaria Fabrich., Bromopsis (Dumort.) Fourr., Ceratochloa P. Beauv., Forasaccus Bub., Genea (Dumort.) Dumort., Libertia Lejeune, Michelaria Dumort., Nevskiella Krecz & Vved., Serrafalcus Parl., Stenofestuca (Honda) Nakai, Triniusa Steud., Trisetobromus Nevski

Excluding Boissiera

Habit, vegetative morphology. Annual, or perennial; rhizomatous, or stoloniferous, or caespitose, or decumbent. Culms 3–190 cm high; herbaceous; branched above, or unbranched above. Culm nodes hairy (rarely), or glabrous. Culm internodes solid (rarely), or hollow. Leaves not basally aggregated; auriculate, or non-auriculate. Sheath margins joined. Sheaths usually hairy. Leaf blades linear; apically flat; broad, or narrow; 1–15 mm wide; usually flat, or rolled (somewhat involute, or convolute); without cross venation; persistent; rolled in bud. Ligule an unfringed membrane; not truncate; 1–9 mm long.

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

Inflorescence. Inflorescence reduced to a single spikelet (very rarely), or few spikeleted, or many spikeleted; a single raceme (rarely), or paniculate; open, or contracted; when contracted more or less ovoid, or spicate, or more or less irregular; with capillary branchlets, or without capillary branchlets. Primary inflorescence branches borne distichously, or inserted all around the main axis. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets secund (falling to one side), or not secund; pedicellate.

Female-fertile spikelets. Spikelets (5–)10–70 mm long; compressed laterally; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; hairy, or hairless; the rachilla extension with incomplete florets. Hairy callus absent.

Glumes two; very unequal (usually), or more or less equal (rarely); shorter than the adjacent lemmas; free; pointed; awnless; carinate, or non-carinate; similar (herbaceous, persistent). Lower glume 1–5(–7) nerved. Upper glume 3–7(–9) nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped; usually awned, or awnless.

Female-fertile florets 3–30 (rarely 1–2). Lemmas similar in texture to the glumes to decidedly firmer than the glumes (herbaceous to subcoriaceous, the margins sometimes membranous); not becoming indurated; incised (usually), or entire (rarely); when incised, 2 lobed; when incised deeply cleft, or not deeply cleft; awnless, or mucronate, or awned. Awns when present, 1, or 3 (B. danthoniae, which may have two additional awnlets); median, or median and lateral (rarely); (the median) from a sinus, or dorsal; from near the top (generally ‘subapical’, but sometimes only very marginally so); non-geniculate; much shorter than the body of the lemma to much longer than the body of the lemma; entered by several veins. Lemmas hairy, or hairless; carinate (Ceratochloa), or non-carinate; without a germination flap; 5–15 nerved. Palea present; relatively long to conspicuous but relatively short; entire to apically notched; awnless, without apical setae; 2-nerved; 2-keeled. Lodicules present; 2; free; fleshy, or membranous; glabrous; not toothed; not or scarcely vascularized. Stamens 1–3. Anthers 0.3–7 mm long; not penicillate. Ovary apically hairy; with a conspicuous apical appendage (above the styles, these lateral to it). Styles free to their bases. Stigmas 2; white.

Fruit, embryo and seedling. Fruit adhering to lemma and/or palea; medium sized; longitudinally grooved; compressed laterally; with hairs confined to a terminal tuft. Hilum long-linear. Embryo small; waisted (rarely), or not waisted. Endosperm hard; without lipid; containing only simple starch grains. Embryo without 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 narrow; erect; 3–12 veined.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells of similar wall thickness costally and intercostally (thin walled). Intercostal zones with typical long-cells (these often large). Mid-intercostal long-cells rectangular, or fusiform; having straight or only gently undulating walls. Microhairs absent. Stomata common; 43–48 microns long. Subsidiaries parallel-sided. Guard-cells overlapped by the interstomatals. Intercostal short-cells common, or absent or very rare; not paired (when present); silicified (often, when present). Intercostal silica bodies usually mainly tall-and-narrow. Crown cells present, or absent. 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 (commonly), or rounded, or tall-and-narrow, or crescentic.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. 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; with one bundle only. Bulliforms present in discrete, regular adaxial groups (in the furrows); 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; 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 (4 species).

Cytology. Chromosome base number, x = 7. 2n = 14, 28, 42, 56, and 70. 2, 4, 6, 8, and 10 ploid. Chromosomes from ‘very small’ to ‘large’. Haploid nuclear DNA content 1.8–7 pg (39 species, mean 4.0). Mean diploid 2c DNA value 9.8 pg (11 species, (6.5–12.5). Nucleoli disappearing before metaphase.

Classification. Watson & Dallwitz (1994): Pooideae; Triticodae; Bromeae. Soreng et al. (2015): Pooideae; Triticodae; Bromeae. About 150 species.

Distribution, phytogeography, ecology. North temperate, tropical mountains, South America.

Commonly adventive. Mesophytic, or xerophytic; shade species and species of open habitats.

Economic aspects. Significant weed species: B. arvensis, B. catharticus, B. commutatus, B. danthoniae, B. diandrus, B. erectus, B. hordeaceus, B. inermis, B. japonicus, B. lanceolatus, B. madritensis, B. pectinatus, B. rigidus, B. rubens, B. secalinus, B. squarrosus, B. sterilis, B. tectorum (several species with injurious callus or awns. Cultivated fodder: B. unioloides; B. inermis cultivated for hay. Important native pasture species: B. danthoniae, B. inermis, B. carinatus, B. catharticus, B. pectinatus, B. tectorum etc. Grain crop species: B. mango - formerly grown as a cereal in Chile.

Hybrids. Supposed intergeneric hybrid with Festuca: ×Bromofestuca Prodan.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia graminis, Puccinia coronata, Puccinia striiformis, Puccinia brachypodii-phoenicoidis, Puccinia hordei, and Puccinia recondita. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae — Tilletia and Urocystis. Ustilaginaceae — Ustilago.

References, etc. Morphological/taxonomic: Wagnon 1952, Smith 1970. Leaf anatomical: Metcalfe 1960; studied by us - B. diandrus Roth, B. erectus Huds. (= Zerna), B. mollis L. (= B. hordeaceus L.), B. unioloides Kunth.

Special comments. Forms with relatively straight-sided, distally widened spikelets, relatively long, long-awned lemmas and relatively fewer-veined glumes are often referred to Anisantha.

Illustrations. • Bromus arvensis, general aspect: Eng. Bot. (1872). • Inflorescence and spikelet (B. catharticus): Gardner, 1952. • B. catharticus: Gibbs Russell et al., 1990. • B. commutatus, general aspect: Eng. Bot. (1872). • Bromus diandrus: Bor, Flora of Iraq (1968). • B. diandrus, B. hordeaceus Gardner, 1952. • B. (Anisantha) diandrus, general aspect: Eng. Bot. (1872). • B. erecta, general aspect: Eng. Bot. (1872). • B. hordeaceus (as B. mollis), general aspect: Eng. Bot. (1872). • B. hordeaceus ssp. ferronii (as B. mollis var. ferronii): Eng. Bot. (1872). • B. (Anisantha) madritensis, general aspect: Eng. Bot. (1872). • B. racemosus, general aspect: Eng. Bot. (1872). • B. secalinus, general aspect: Eng. Bot. (1872). • cf. B. secalinus (as var. velutinus): Eng. Bot. (1872). • B. (Anisantha) sterilis, general aspect: Eng. Bot. (1872). • B. ramosa (as B. asper), general aspect: Eng. Bot. (1872). • Ligule region (B. unioloides). • Ligule region (B. unioloides). • Spikelet of B. unioloides. • Spikelet details (B. unioloides). Bromus unioloides. Tip of spikelet, opened to expose rachilla prolongation (below left of the terminal floret). • Lemma tip and awn (B. inermis). • Rachilla tip (B. unioloides). Bromus unioloides. Uppermost floret (left), rachilla prolongation with undeveloped floret (right). • Mature ovary of Bromus unioloides. Bromus unioloides. Hairy, terminally appendaged ovary with subterminal styles. • Ovary and lodicules of B. unioloides. Bromus unioloides. Membranous lodicules at base of immature ovary. • Caryopsis. • Germination in Bromus unioloides. Bromus unioloides. Radicle (lower right) emerging through the split lemma. • Bromus unioloides, abaxial epidermis of leaf blade: this project. • Bromus unioloides: Abaxial epidermis of leaf blade, silica bodies). • Bromus diandrus, abaxial epidermis of leaf blade, silica bodies. • Grass pollen antigens: Watson and Knox (1976). • Grass pollen antigens: cross-reactions against anti-Lolium serum. IMMUNOELECTROPHORESIS OF GRASS POLLEN EXTRACTS (DIFFUSIBLE ANTIGENS).

Each slide with rabbit antiserum in the trough, Lolium perenne pollen extract (control) in the upper well, and comparable extracts from other genera in the lower wells, as indicated. Results are compared using raw extract (left) with those using boiled extract (right). Antigens allergenic in humans are concentrated in the heat-stable components. For experimental details and discussion of the taxonomic patterns among cross-reactions, see Watson and Knox (1976) and Watson (1983). • Grass pollen antigens: cross-reactions against anti-Lolium serum. IMMUNOELECTROPHRESIS OF GRASS POLLEN EXTRACTS (DIFFUSIBLE ANTIGENS).

Each slide with rabbit antiserum in the trough, Lolium perenne pollen extract (control) in the upper well, and comparable extracts from other genera in the lower wells, as indicated. For experimental details and discussion of the taxonomic patterns among cross-reactios, see Watson and Knox (1976) and Watson (1983). • Heat stable grass pollen antigens (allergens): cross-reactions against anti-Lolium serum. IMMUNOELECTROPHRESIS OF GRASS POLLEN EXTRACTS (DIFFUSIBLE ANTIGENS-HEAT-STABLE COMPONENT).

Each slide with rabbit antiserum in the trough, boiled Lolium perenne pollen extract (control) in the upper well, and comparable boiled extracts from other genera in the lower wells, as indicated. For experimental details and discussion of the taxonomic patterns among cross-reactios, see Watson and Knox (1976) and Watson (1983).

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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