Aira L.
The Greek name for Lolium temulentum.
Including Airella (Dumort.) Dumort., Aspris Adans., Caryophyllea Opiz, Fiorinia Parl., Fussia Schur, Salmasia Bub.
Habit, vegetative morphology. Small, slender annual; caespitose. Culms 2–40 cm high; herbaceous; unbranched above. Culm nodes glabrous. Culm internodes hollow. Leaves mostly basal, or not basally aggregated; non-auriculate. Leaf blades linear; narrow; 0.3–2 mm wide; setaceous; flat, or folded, or rolled; without abaxial multicellular glands; without cross venation; persistent; rolled in bud, or once-folded in bud; an unfringed membrane; not truncate (acute); 2.4–5 mm long.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets; inbreeding.
Inflorescence. Inflorescence paniculate; open, or contracted; when contracted, spicate to more or less irregular; with conspicuously divaricate branchlets, or without conspicuously divaricate branchlets; with capillary branchlets. Primary inflorescence branches borne distichously. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.
Female-fertile spikelets. Spikelets 1.6–3.5 mm long; compressed laterally; disarticulating above the glumes; disarticulating between the florets; with conventional internode spacings. The upper floret not stipitate. Rachilla prolonged beyond the uppermost female-fertile floret, or terminated by a female-fertile floret; hairless; the rachilla extension when present, naked. Hairy callus present, or absent. Callus short; blunt.
Glumes two; more or less equal; about equalling the spikelets, or exceeding the spikelets; long relative to the adjacent lemmas; pointed; awnless; carinate, or non-carinate; similar (membranous, delicate). Lower glume 1–3 nerved. Upper glume 1–3 nerved. Spikelets with female-fertile florets only; without proximal incomplete florets.
Female-fertile florets 2. Lemmas decidedly firmer than the glumes (becoming papery); not becoming indurated; entire, or incised; awnless, or awned. Awns when present, 1; dorsal; from well down the back; geniculate; much shorter than the body of the lemma to much longer than the body of the lemma; entered by one vein. Lemmas hairless; carinate to non-carinate; 5 nerved. Palea present; relatively long; tightly clasped by the lemma; apically notched; awnless, without apical setae; 2-nerved. Lodicules present; 2; free; membranous; glabrous; not toothed. Stamens 3. Anthers 0.2–1.7 mm long; not penicillate. Ovary glabrous. Styles free to their bases. Stigmas 2; white.
Fruit, embryo and seedling. Fruit adhering to lemma and/or palea; small; fusiform; longitudinally grooved; compressed dorsiventrally. Hilum short. Embryo small; not waisted. Endosperm hard; with lipid; containing compound starch grains. Embryo with an epiblast; without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins meeting.
Seedling 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; 3–5 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 fusiform; having markedly sinuous walls, or having straight or only gently undulating walls. Microhairs absent. Stomata absent or very rare, or common; 45–54 microns long (in A. cupaniana). Subsidiaries parallel-sided, or dome-shaped. Guard-cells overlapped by the interstomatals. Intercostal short-cells absent or very rare. Intercostal silica bodies absent. Costal short-cells conspicuously in long rows, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies confined to the central file(s) of the costal zones; horizontally-elongated crenate/sinuous.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs, or ‘nodular’ in section; with the ribs more or less constant in size. Midrib conspicuous; with one bundle only. Bulliforms not present in discrete, regular adaxial groups. Many of the smallest vascular bundles unaccompanied by sclerenchyma, or all the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent. Sclerenchyma all associated with vascular bundles.
Phytochemistry. Tissues of the culm bases with abundant starch, or with little or no starch. Leaves without flavonoid sulphates (1 species).
Cytology. Chromosome base number, x = 7. 2n = 14 and 28. 2 and 4 ploid. Chromosomes ‘large’. Haploid nuclear DNA content 2.7–3.2 pg (4 species, mean 2.9). Mean diploid 2c DNA value 6 pg, or 5.9 pg (A. elegantissima, A. praecox).
Taxonomy. Pooideae; Poodae; Aveneae. Hairgrasses.
Distribution, ecology, phytogeography. 8 species; North and South temperate. Commonly adventive. Mesophytic to xerophytic; species of open habitats. Sandy soils.
Holarctic, Paleotropical, Cape, and Antarctic. Boreal and Tethyan. African. Euro-Siberian and Atlantic North American. Macaronesian, Mediterranean, and Irano-Turanian. Sudano-Angolan and West African Rainforest. Patagonian. European. Southern Atlantic North American and Central Grasslands. Sahelo-Sudanian, Somalo-Ethiopian, and South Tropical African.
Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia graminis and Puccinia striiformis. Smuts from Tilletiaceae. Tilletiaceae — Tilletia.
References, etc. Leaf anatomical: this project.
Illustrations. • General aspect. • Inflorescence detail. • Abaxial epidermis of leaf blade. Aira cupiana. • Transverse section of leaf blade
Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘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.’ http://biodiversity.uno.edu/delta/. Version: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).
