The grass genera of the world
Habit, vegetative morphology. Perennial; rhizomatous, or stoloniferous (with thick, brittle rhizomes). Culms robust, 30–80 cm high; herbaceous; unbranched above. Culm nodes glabrous. Culm internodes hollow. Young shoots extravaginal. Leaves not basally aggregated; non-auriculate. Leaf blades linear; narrow (purplish); 2–7(–13) mm wide; flat; not pseudopetiolate; without cross venation; persistent; rolled in bud. Ligule an unfringed membrane; not truncate (usually lacerate); (2–)3–5(–8) mm long.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate; open (with long branches, the lower often deflexed); espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.
Female-fertile spikelets. Spikelets 2.5–8 mm long; compressed laterally to not noticeably compressed; disarticulating above the glumes. Rachilla prolonged beyond the uppermost female-fertile floret; hairless; the rachilla extension with incomplete florets. Hairy callus present. Callus short; blunt.
Glumes two; more or less equal; shorter than the spikelets; long relative to the adjacent lemmas; hairless; pointed; awnless; non-carinate; similar (membranous, ovate, apices scarious). Lower glume longer than half length of lowest lemma; 1 nerved. Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets 1; merely underdeveloped (vestigial, at the rachilla tip).
Female-fertile florets 2–7. Lemmas similar in texture to the glumes to decidedly firmer than the glumes; not becoming indurated; entire; blunt; mucronate; hairy (at the base), or hairless; non-carinate; without a germination flap; 3–5 nerved. Palea present; relatively long; apically notched; not indurated; 2-nerved; 2-keeled. Lodicules present; 2; free; membranous; glabrous; toothed, or not toothed; not or scarcely vascularized. Stamens 3. Anthers 1.2–2 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small (1.5–2 mm long); fusiform; not grooved. Hilum short. Embryo small; without an epiblast; without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins meeting.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals narrower, more regularly fusiform); differing markedly in wall thickness costally and intercostally (the costals with thick, pitted walls, the intercostal walls thin and unpitted). Mid-intercostal long-cells rectangular (occasionally), or fusiform (mostly); having straight or only gently undulating walls. Microhairs absent. Stomata common. Subsidiaries parallel-sided. Guard-cells overlapped by the interstomatals (but only slightly so). Intercostal short-cells absent or very rare. Costal short-cells neither distinctly grouped into long rows nor predominantly paired (solitary, infrequent). Costal silica bodies absent to poorly developed (i.e. in the infrequent costal short-cells in the material of A. fulva seen).
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll without adaxial palisade. Leaf blade nodular in section (with broad, rounded adaxial and abaxial ribs); with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups (fairly ill defined), or not present in discrete, regular adaxial groups; in simple fans (the groups irregular). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (heavy, with all the bundles); forming figures (mostly I-shaped). Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 7. 2n = 42 and 63. 6 and 9 ploid. Chromosomes large.
Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Poeae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Poinae. 1 species (A. fulva).
Distribution, phytogeography, ecology. Arctic and subarctic.
Helophytic; species of open habitats; glycophytic. Marshy places and pool margins.
Hybrids. Intergeneric hybrids with Dupontia (×Arctodupontia Tsvelev).
References, etc. Leaf anatomical: studied by us.
Illustrations. • A. fulva, as Colpodium: Lamson-Scribner (1899)
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. delta-intkey.com/grass’.