The grass genera of the world

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L. Watson and M. J. Dallwitz

Bromus L.

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

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; 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; 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, 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. Spikelets without proximal incomplete florets.

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 hairy; with a conspicuous apical appendage (the styles 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.

Taxonomy. Pooideae; Triticodae; Bromeae.

Distribution, ecology, phytogeography. About 150 species; North temperate, tropical mountains, South America. Commonly adventive. Mesophytic, or xerophytic; shade species and species of open habitats.

Holarctic, Paleotropical, Neotropical, Cape, Australian, and Antarctic. Boreal, Tethyan, and Madrean. African and Indomalesian. Arctic and Subarctic, Euro-Siberian, Eastern Asian, Atlantic North American, and Rocky Mountains. Macaronesian, Mediterranean, and Irano-Turanian. Saharo-Sindian, Sudano-Angolan, and West African Rainforest. Indo-Chinese, Malesian, and Papuan. Caribbean, Venezuela and Surinam, Central Brazilian, Pampas, and Andean. North and East Australian and South-West Australian. New Zealand and Patagonian. European and Siberian. Canadian-Appalachian, Southern Atlantic North American, and Central Grasslands. Sahelo-Sudanian, Somalo-Ethiopian, and South Tropical African. Temperate and South-Eastern Australian.

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.

Economic importance. 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.

References, etc. Morphological/taxonomic: Wagnon 1952, Smith 1970. Leaf anatomical: Metcalfe 1960; this project.

Illustrations. • General aspect (B. catharticus). • General aspect (B. diandrus, B. hordeaceus). • Inflorescence and spikelet (B. catharticus). • 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 B. 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 B. unioloides. Bromus unioloides. Radicle (lower right) emerging through the split lemma. • Abaxial epidermis of leaf blade (B. unioloides). • Abaxial epidermis of leaf blade, silica bodies (B. unioloides). • Abaxial epidermis of leaf blade, silica bodies (B. diandrus). • Pollen antigens. • 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


This description is offered for casual browsing only. We strongly advise against extracting comparative information from it. This is much more easily achieved using 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 specified attributes, summaries of attributes within groups of taxa, geographical distribution, classification, and species sampled for anatomy.

Cite this publication as: ‘Watson, L., 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: 5th February 2014. http://delta-intkey.com’.

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