The grass genera of the world
Habit, vegetative morphology. Annual, or perennial; caespitose, or decumbent. Culms 5–30 cm high; herbaceous; unbranched above. Leaves not basally aggregated; non-auriculate. Leaf blades linear; narrow; about 2.5 mm wide (to 12 cm long); flat; without cross venation; persistent. Ligule an unfringed membrane; usually lacerate; 1–3 mm long.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate; open (up to 10 by 7 cm); with conspicuously divaricate branchlets; with capillary branchlets; espatheate; not comprising partial inflorescences and foliar organs. Spikelets not secund; pedicellate (the pedicels longer than the spikelets, clavate).
Female-fertile spikelets. Spikelets 1–2 mm long; compressed laterally; disarticulating above the glumes; disarticulating between the florets; with distinctly elongated rachilla internodes between the florets. The upper floret conspicuously stipitate. Rachilla terminated by a female-fertile floret; hairless.
Glumes two; more or less equal; exceeding the spikelets; long relative to the adjacent lemmas; hairless (scabridulous on the keel); subobtuse; awnless; carinate; similar. Lower glume 3 nerved. Upper glume 3 nerved. Spikelets with female-fertile florets only.
Female-fertile florets 2. Lemmas elliptic, widest near the tip by contrast with Airopsis, membranous; similar in texture to the glumes; not becoming indurated; slightly incised; blunt; more or less truncate, but shallowly 3 lobed; not deeply cleft; awnless; hairless; glabrous; non-carinate; without a germination flap; 5 nerved. Palea present; relatively long; tightly clasped by the lemma; awnless, without apical setae; not indurated; 2-nerved; 2-keeled. Stamens 3. Anthers 0.5–1 mm long. Ovary apically glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit pyriform; compressed dorsiventrally (rounded abaxially, flat ventrally). Hilum short. Embryo small.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present (very abundant); costal and intercostal (but mainly intercostal, being excluded from the costae by prickles). Intercostal papillae over-arching the stomata; several per cell (quite large, thick walled, circular, in one row of 2–5 per cell). Mid-intercostal long-cells rectangular to fusiform; having markedly sinuous walls and having straight or only gently undulating walls. Microhairs absent. Stomata common. Subsidiaries non-papillate; mostly more or less parallel-sided. Guard-cells overlapped by the interstomatals. Intercostal short-cells common; mostly apparently not paired (solitary). The costal zones dominated by chains of blunt prickles. Costal short-cells neither distinctly grouped into long rows nor predominantly paired (infrequent, amid the prickles). Costal silica bodies present and well developed (but examples few and far between); horizontally-elongated crenate/sinuous (short, often more or less imperfect).
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size (tall). Midrib not readily distinguishable; with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups (perhaps, in the furrows), or not present in discrete, regular adaxial groups (?); if present, in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent (the sclerenchyna confined to small adaxial strands, and small abaxial strands and girders). Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 7. 2n = 14. 2 ploid.
Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Aveneae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Airinae. 2 species.
Distribution, phytogeography, ecology. Mediterranean.
Mesophytic (in damp places); glycophytic.
References, etc. Leaf anatomical: this project.
Special comments. Morphological description compiled from Flora Europaea and Clayton & Renvoize (1987). Illustrations. • A. agrostidea: Coste (1906), Fl. de France. • A. agrostidea, 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’.