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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; studied by us - S. cereale L.

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

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: 11th December 2017.’.