The grass genera of the world
Habit, vegetative morphology. Perennial; rhizomatous, or stoloniferous. Culms 5–50(–80) cm high; herbaceous. Leaves non-auriculate. Sheath margins joined. Sheaths often purplish. Leaf blades linear; narrow; 1–5 mm wide; flat, or folded; without cross venation. Ligule an unfringed membrane; smooth, glabrous, truncate, or not truncate; 1–3 mm long.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate; open to contracted; espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.
Female-fertile spikelets. Spikelets 4–9 mm long; compressed laterally to not noticeably compressed; disarticulating above the glumes. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension naked. Hairy callus present (with a crown of coarswe hairs), or absent. Callus short; blunt.
Glumes two; relatively large; very unequal to more or less equal; (the upper) about equalling the spikelets; (the upper) long relative to the adjacent lemmas (exceeding them); pointed, or not pointed; awnless; non-carinate; similar (membranous, with wide hyaline margins). Lower glume 1–3 nerved. Upper glume 1–3 nerved. Spikelets with female-fertile florets only.
Female-fertile florets (1–)2(–4). Lemmas acute; less firm than the glumes to similar in texture to the glumes (scarious); not becoming indurated; entire; pointed; awnless, or mucronate, or awned (via the excurrent mid-vein). Awns when present, 1; median; apical; non-geniculate; to 0.6 mm long, much shorter than the body of the lemma. Lemmas hairy (at least at the base), or hairless; non-carinate; without a germination flap; 3 nerved, or 5 nerved. Palea present; relatively long (but shorter than the lemma); 2-nerved; 2-keeled. Lodicules present; 2; free; membranous; glabrous; toothed (with a lateral lobe), or not toothed; not or scarcely vascularized. Stamens 3. Anthers 1.5–3 mm long. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small (1.5–2.5 mm long); indistinctly longitudinally grooved to not grooved; sub- trigonous. Hilum short. Pericarp fused (?). Embryo without an epiblast (Decker 1964); without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins meeting.
Abaxial leaf blade epidermis. Costal/intercostal zonation lacking (save that the midrib zone is barely distinguishable, by rather narrower long-cells). Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally (fairly thick walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs absent. Stomata absent or very rare. Intercostal short-cells common; not paired (solitary). Costal short-cells neither distinctly grouped into long rows nor predominantly paired (mostly solitary). Costal silica bodies horizontally-elongated crenate/sinuous (very short with few crenations, or imperfect), or rounded, or tall-and-narrow to crescentic (a few).
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Leaf blade nodular in section to adaxially flat (with a constriction on either side of the midrib, otherwise scarcely ribbed). Midrib conspicuous (with a rib and a slight keel); with one bundle only. Bulliforms not present in discrete, regular adaxial groups (other than the conspicuous hinges flanking the midrib). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the bundles); nowhere forming figures (the girders slender). Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 7. 2n = 42, 44, 88, and 132. 6, 12, and 19 ploid (?). Chromosomes large.
Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Poeae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Poinae. 2 species.
Distribution, phytogeography, ecology. Arctic.
Helophytic; species of open habitats; slightly glycophytic, or halophytic.
Hybrids. Intergeneric hybrid with Arctophila: ×Arctodupontia Tsvelev. With Arctopoa (= Poa): ×Dupontopoa N.S. Probatova (exemplified by Poa labradorica Steudel, with ×Dupontopoa dezhnevii representing taxonomic errors: see Darbyshire et al. 1992, Darbyshire and Cayouette 1992).
References, etc. Leaf anatomical: Metcalfe 1960; this project.
Special comments. Fruit data wanting. Illustrations. • D. fisheri: Vasey, Illust. N. Amer. Grasses (1892)
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’.