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The grass genera of the world

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

Psilurus Trin.

From the Greek psilos, slender and oura, tail, referring to the slender spike.

~ Festuca

Type species: Type: P. nardoides Trin., nom. illeg..

Including Asprella Host

Habit, vegetative morphology. Slender annual; caespitose (or single culms). Culms 5–45 cm high; herbaceous. Culm nodes glabrous. Culm internodes solid, or hollow. Leaves non-auriculate. Sheaths not keeled. Leaf blades linear (filiform); apically cucullate; narrow; about 0.2–1 mm wide; setaceous; rolled (convolute); without cross venation; persistent. Ligule present; an unfringed membrane; truncate; 0.2–0.3 mm long.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant, or all alike in sexuality; hermaphrodite, or hermaphrodite and sterile (the basal spikelets sometimes reduced).

Inflorescence. Inflorescence a single spike (thin, wiry, ultimately disarticulating, the spikelets initially sunken, ultimately spreading). Rachides hollowed. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes tardily disarticulating; disarticulating at the joints. Spikelets solitary; not secund; distichous; sessile; not imbricate.

Female-fertile spikelets. Spikelets 3.5–6.8 mm long; adaxial (the single (‘upper’) glume on the outside); compressed laterally; disarticulating above the glumes (the terminal spikelet), or falling with the glumes (the lower spikelets); with distinctly elongated rachilla internodes between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets, or naked. Hairy callus absent. Callus short; blunt (glabrous).

Glumes one per spikelet (except for the terminal spikelet, with two); (the upper, only glume) shorter than the adjacent lemmas (very small); dorsiventral to the rachis; pointed; awnless; non-carinate. Upper glume 1 nerved. Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets when present, distal to the female-fertile florets. The distal incomplete florets merely underdeveloped (rudimentary).

Female-fertile florets 1(–2). Lemmas linear-lanceolate; membranous to leathery; not becoming indurated; entire, or incised; not deeply cleft; awned. Awns 1; median; from a sinus, or apical; non-geniculate; straight; hairless (scabrous); much shorter than the body of the lemma to much longer than the body of the lemma (2.3–5.5 mm long); entered by one vein. Awn bases flattened. Lemmas hairless; carinate; 3 nerved. Palea present; relatively long (as long as the lemma); tightly clasped by the lemma; entire; awnless, without apical setae; thinner than the lemma (membranous); not indurated; 2-nerved; 2-keeled. Palea keels wingless. Lodicules present; 2; membranous; toothed. Stamens 1. Anthers 0.4–2.2 mm long; not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white.

Fruit, embryo and seedling. Fruit slightly adhering to lemma and/or palea; small (about 4 mm long); linear, or ellipsoid; longitudinally grooved to not grooved; compressed laterally; scabrous. Hilum long-linear. Embryo small; not waisted. Endosperm hard; with lipid; containing compound starch grains. Embryo with an epiblast.

Seedling with a short mesocotyl; with a tight coleoptile. First seedling leaf with a well-developed lamina. The lamina narrow; erect; 3 veined.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells fusiform; having markedly sinuous walls. Microhairs absent. Stomata absent or very rare. Intercostal short-cells common; in cork/silica-cell pairs, or not paired (solitaries); silicified (when paired), or not silicified. Costal short-cells predominantly paired, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies horizontally-elongated crenate/sinuous, horizontally-elongated smooth, rounded, and tall-and-narrow (and some rather square); not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Leaf blade ‘nodular’ in section, or adaxially flat; with the ribs more or less constant in size. Midrib conspicuous; with one bundle only. Bulliforms poorly developed, not present in discrete, regular adaxial groups. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders absent. Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 7. 2n = 14 and 28. 2 and 4 ploid. Chromosomes ‘large’.

Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Poeae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Loliinae. 1 species (P. incurvus).

Distribution, phytogeography, ecology. Mediterranean to Afghanistan.

Commonly adventive. Species of open habitats. Dry places.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia graminis and Puccinia hordei.

References, etc. Leaf anatomical: studied by us.

Illustrations. • Spikelet in situ (P. incurvus). • P. incurvus, as P. nardoides (with Parapholis incurva, as Lepturus): Thomé (1885), Flora von Deutschland, Osterreich und der Schweiz. • P. incurvus, TS 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: 11th December 2017.’.