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The grass genera of the world

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

Triticum L.

Triticum: classical Latin name for wheat.

Including Crithodium Link, Deina Alefeld, Frumentum Krause, Gigachilon Seidl, Nivieria Ser., Spelta Wolf

Habit, vegetative morphology. Annual; caespitose. Culms 40–170 cm high; herbaceous; unbranched above. Culm nodes hairy, or glabrous. Culm internodes solid, or hollow. Leaves not basally aggregated; auriculate. Leaf blades narrowly to broadly linear; apically flat; broad to narrow; 2–20 mm wide; flat; without cross venation; persistent; rolled in bud. Ligule an unfringed membrane; truncate; 0.6–2 mm long.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant, or all alike in sexuality; hermaphrodite, or hermaphrodite and sterile (often incomplete at the base of the spike). Plants inbreeding.

Inflorescence. Inflorescence a single spike (elongated). Rachides hollowed. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes with substantial rachides (these flattened or hollowed); disarticulating (Crithodium), or persistent; when fragile, disarticulating at the joints (above or below the spikelet). Spikelets solitary; not secund; distichous; sessile.

Female-fertile spikelets. Spikelets 9–16 mm long; compressed laterally; disarticulating above the glumes, or falling with the glumes, or not disarticulating (in cultivated forms); not disarticulating between the florets, or disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets. Hairy callus absent. Callus very short; blunt.

Glumes two; more or less equal; shorter than the adjacent lemmas, or long relative to the adjacent lemmas; lateral to the rachis; without conspicuous tufts or rows of hairs; not pointed (obtuse, truncate or bidentate via the lateral nerves); not subulate; awned (or mucronate), or awnless; carinate (at least above, before the grain expands); with the keel conspicuously winged (and crested, in Gigachilon), or without a median keel-wing; similar (ovate or oblong, chartaceous or rarely membranous). Lower glume 5–11 nerved. Upper glume 5–11 nerved. Spikelets usually with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets usually 1, or 2; merely underdeveloped.

Female-fertile florets 1 (Crithodium), or 2–6. Lemmas similar in texture to the glumes to decidedly firmer than the glumes; becoming indurated; entire to incised (1 to several dentate, or acuminate); awnless, or awned. Awns when present, 1; median; from a sinus, or 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 hairy, or hairless (but scabrid); non-carinate, or carinate (at least above); 5–11 nerved; with the nerves non-confluent. Palea present; relatively long; entire (not split or divided at maturity), or apically notched (Crithodium); 2-nerved; 2-keeled. Palea keels somewhat winged. Lodicules present; 2; free; membranous; ciliate; not toothed. Stamens 3. Anthers 2–4.5 mm long; not penicillate. Ovary apically hairy; with a conspicuous apical appendage (fleshy below the styles). Styles free to their bases. Stigmas 2; white.

Fruit, embryo and seedling. Fruit free from both lemma and palea (free threshing); medium sized to large (to 11 mm long); ellipsoid; longitudinally grooved; compressed dorsiventrally, or not noticeably compressed; with hairs confined to a terminal tuft. Hilum long-linear. Embryo large to small (to 1/3 the caryopsis length); 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 tight coleoptile. First seedling leaf with a well-developed lamina. The lamina narrow; erect; ‘many’.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular, or rectangular and fusiform; having markedly sinuous walls, or having straight or only gently undulating walls, or having markedly sinuous walls and having straight or only gently undulating walls. Microhairs absent. Stomata common; 63–69 microns long. Subsidiaries parallel-sided, or dome-shaped (low). Guard-cells overlapped by the interstomatals. Intercostal short-cells common (e.g. T. polonicum), or absent or very rare (usually); when present, mostly in cork/silica-cell pairs; silicified. Intercostal silica bodies rounded (or oval), or crescentic. Crown cells present. Costal zones with short-cells. Costal short-cells predominantly paired (T. polonicum), or neither distinctly grouped into long rows nor predominantly paired (or varying from vein to vein). Costal silica bodies horizontally-elongated crenate/sinuous, or horizontally-elongated smooth, or rounded, or crescentic; not sharp-pointed.

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; with the ribs more or less constant in size. Midrib conspicuous; with one bundle only, or having a conventional arc of bundles. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups (in the furrows); in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present (rarely), or absent; if present, 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. Leaves without flavonoid sulphates (1 species).

Cytology. Chromosome base number, x = 7. 2n = 42, or 14 and 28 (Crithodium). 6 ploid, or 2 and 4 ploid (Crithodium). Haplomic genome content A (Crithodium), or A and B (Gigichilon), or A, B, and D (Triticum sensu stricto). Haploid nuclear DNA content 4.9–6.2 pg (8 species, mean 5.9). Mean diploid 2c DNA value 12.2 pg (3 species, 9.8–13.8).

Classification. Watson & Dallwitz (1994): Pooideae; Triticodae; Triticeae. Soreng et al. (2015): Pooideae; Triticodae; Triticeae; Triticinae. 8 species.

Distribution, phytogeography, ecology. Europe, Mediterranean, Western Asia.

Commonly adventive. Mesophytic, or xerophytic; species of open habitats. Stony hillsides, dry grassland, weedy places.

Economic aspects. Grain crop species: several, but modern agriculture largely confined to T. aestivum (Bread Wheat) and T. durum (Macaroni Wheat).

Hybrids. Intergeneric hybrids with AegilopsAegilotriticum Wagner ex Tschermak), AgropyronAgrotriticum Ciferri & Giacom.), Elymus, ElytrigiaTrititrigia Tsvelev), HordeumTritordeum Aschers. & Graebn.), Lophopyrum, SecaleTriticosecale Wittmack), Taeniatherum. See also ×Elymotriticum P. Fourn., ×Agrotrisecale Ciferri & Giacom. (Agropyron × Secale × Triticum), ×Oryticum Wang & Tang (supposedly Oryza × Triticum).

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

References, etc. Morphological/taxonomic: Löve 1984. Leaf anatomical: Metcalfe 1960; this project.

Illustrations. • T. aestivum (Hitchcock and Chase, 1950). • Caryopsis of T. aestivum. • Starch from fruit of T. aestivum. • T. aestivum, abaxial epidermis of leaf blade: 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. delta-intkey.com/grass’.

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