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The grass genera of the world

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

Arctophila Rupr. ex Andersson

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.

Distribution, phytogeography, ecology. Arctic and subarctic.

Helophytic; species of open habitats; glycophytic. Marshy places and pool margins.

Hybrids. Intergeneric hybrids with DupontiaArctodupontia Tsvelev).

References, etc. Leaf anatomical: this project.

Illustrations. • A. fulva, as Colpodium: Lamson-Scribner (1899)


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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’.

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