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The grass genera of the world

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

Arctagrostis Griseb.

Habit, vegetative morphology. Robust perennial; rhizomatous. Culms 10–120 cm high; herbaceous. Culm internodes hollow. Leaves non-auriculate. Leaf blades linear; narrow; 2–7 mm wide; flat; without cross venation. Ligule an unfringed membrane; truncate; 2–5 mm long.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets; exposed-cleistogamous, or chasmogamous (?).

Inflorescence. Inflorescence paniculate; open, or contracted; when contracted spicate, or more or less irregular; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets 2.2–7 mm long; purplish; not noticeably compressed; disarticulating above the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent. Callus short.

Glumes present; two; more or less equal; shorter than the adjacent lemmas; hairless (usually glabrous); pointed; awnless; carinate; similar. Lower glume 1 nerved. Upper glume 3 nerved. Spikelets with female-fertile florets only; without proximal incomplete florets.

Female-fertile florets 1. Lemmas similar in texture to the glumes to decidedly firmer than the glumes; not becoming indurated; entire, or incised; when entire pointed, or blunt; awnless, or mucronate; hairless; carinate; without a germination flap; 3–5 nerved. Palea present (similar to lemma); relatively long; textured like the lemma; not indurated; 2-nerved; obscurely 2-keeled, or keel-less. Lodicules present; 2; free; membranous; glabrous; not toothed; not or scarcely vascularized. Stamens 2, or 3. Anthers 1–3 mm long; not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small. Hilum short. Embryo small. Endosperm liquid in the mature fruit.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally; differing markedly in wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having straight or only gently undulating walls. Microhairs absent. Stomata common. Subsidiaries parallel-sided. Guard-cells overlapped by the interstomatals. Intercostal short-cells absent or very rare. Costal silica bodies absent (in the material seen).

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma.

Cytology. Chromosome base number, x = 7. 2n = 28, 42, 56, and 63. 4, 8, and 9 ploid. Chromosomes ‘large’.

Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Aveneae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Poinae. 6 species.

Distribution, phytogeography, ecology. Arctic America, Eurasia.

Helophytic, or mesophytic; species of open habitats. Arctic, marshy tundra.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia brachypodii. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae — Urocystis. Ustilaginaceae — Ustilago.

References, etc. Leaf anatomical: this project.

Illustrations. • A. latifolia: Lamson-Scribner (1899), American Grasses II

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: 21st January 2017.’.