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The grass genera of the world

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

Secale L.

Classical Latin name for rye or spelt.

Habit, vegetative morphology. Annual (rarely perennial); caespitose (or the culms solitary). Culms 20–150 cm high; herbaceous; unbranched above. Culm nodes glabrous. Culm internodes hollow. Leaves not basally aggregated; auriculate. Leaf blades linear; apically flat; broad, or narrow; 2.5–20 mm wide; flat, or rolled (convolute); without cross venation; persistent; rolled in bud. Ligule an unfringed membrane; truncate.

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

Inflorescence. Inflorescence a single spike (laterally compressed, distichous). Rachides hollowed. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes disarticulating, or persistent (in cultivated forms); disarticulating at the joints. Spikelets solitary; not secund; distichous; sessile.

Female-fertile spikelets. Spikelets 10–18 mm long; compressed laterally; falling with the glumes (and the joint), or not disarticulating (in cultivated forms). Rachilla prolonged beyond the uppermost female-fertile floret; hairless. Hairy callus absent. Callus very short.

Glumes two; very unequal to more or less equal; shorter than the adjacent lemmas; free; lateral to the rachis; subulate; acuminate to awned; carinate (sharply keeled to the base); similar (membranous). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets 1; merely underdeveloped.

Female-fertile florets 2–3. Lemmas lanceolate, tapered to the awn; less firm than the glumes to similar in texture to the glumes; entire; pointed; awned. Awns 1; median; apical; non-geniculate; hairless (scabrid); much longer than the body of the lemma; entered by several veins. Lemmas hairless; carinate (the keel with rigid, pectinate cilia); 5 nerved; with the nerves non-confluent. Palea present; relatively long; apically notched; not indurated (hyaline); 2-nerved; 2-keeled. Lodicules present; 2; free; membranous; ciliate. Stamens 3. Anthers 2.3–12 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; medium sized to large; ellipsoid; longitudinally grooved; slightly compressed dorsiventrally to not noticeably compressed; with hairs confined to a terminal tuft. Hilum long-linear. Embryo large to small (to 1/3 the length of the caryopsis). 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; with a tight coleoptile. First seedling leaf with a well-developed lamina. The lamina narrow; erect; 9–15 veined (?).

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs absent. Stomata common; 48–49–51 microns long. Subsidiaries low dome-shaped, or parallel-sided. Guard-cells overlapped by the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies rounded (elliptical), or crescentic. Costal short-cells predominantly paired. Costal silica bodies rounded and crescentic; not sharp-pointed.

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; with the ribs very irregular in sizes. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Culm anatomy. Culm internode bundles in one or two rings.

Phytochemistry. Leaves without flavonoid sulphates (1 species).

Cytology. Chromosome base number, x = 7. 2n = 14. 2 ploid. Haplomic genome content R. Chromosomes ‘large’. Haploid nuclear DNA content 7.2–9.5 pg (5 species, mean 8.3). Mean diploid 2c DNA value 16.8 pg (6 species, 14.8–19.0).

Classification. Watson & Dallwitz (1994): Pooideae; Triticodae; Triticeae. Soreng et al. (2015): Pooideae; Triticodae; Triticeae; Hordeinae. 5 species.

Distribution, phytogeography, ecology. Mediterranean, eastern Europe to central Asia, and South Africa.

Commonly adventive. Mesophytic, or xerophytic; species of open habitats. Sandy soils and dry hillsides.

Economic aspects. Grain crop species: S. cereale (Rye).

Hybrids. Intergeneric hybrids with TriticumTriticosecale Wittmack), Agropyron, AegilopsAegilosecale Ciferri & Giacom.), HordeumHordale Ciferri & Giacom.), Elytrigia. ×Agrotrisecale Ciferri & Giacom. = Agropyron × Secale × Triticum.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia graminis, Puccinia striiformis, Puccinia recondita, ‘Uromycesturcomanicum, and ‘Uromycesfragilipes. 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. • S. cereale: Gardner, 1952. • S. africanum: Hook. Ic. Pl. 27 (1901). • General aspect (S. africanum): Gibbs Russell et al., 1990. • Rye inflorescence with Ergot


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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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