Pseudarrhenatherum Rouy
Including Thorea Rouy, Thoreochloa Holub
Sometimes referred to Arrhenatherum
Habit, vegetative morphology. Perennial; caespitose. Culms 30–120(–150) cm high; herbaceous; unbranched above; not tuberous. Culm nodes hairy, or glabrous. Leaves non-auriculate. Leaf blades narrow; 0.6–4 mm wide (with prominent adaxial ribs, by contrast with Arrhenatherum); setaceous, or not setaceous; flat, or rolled (convolute); without cross venation; persistent; ligule present; an unfringed membrane (to finely ciliate).
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate; open (to rather dense); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.
Female-fertile spikelets. Spikelets 5–10 mm long; compressed laterally; disarticulating above the glumes; not disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret.
Glumes two; very unequal; long relative to the adjacent lemmas; pointed (acuminate); awnless; similar (thin). Lower glume 1 nerved, or 3 nerved. Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets, or both distal and proximal to the female-fertile florets. The distal incomplete florets (when present) merely underdeveloped (a single rudiment). Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate; male. The proximal lemmas awned (the awn geniculate, dorsal, from the middle or above); 5–9 nerved (?); similar in texture to the female-fertile lemmas (but apically bifid).
Female-fertile florets 1. Lemmas acute; decidedly firmer than the glumes; not becoming indurated; entire; pointed; awnless, or awned (?). Awns 1; median; dorsal; from near the top; non-geniculate. Lemmas non-carinate; without a germination flap; 5–9 nerved (?). Palea present; relatively long; awnless, without apical setae; not indurated; 2-nerved; 2-keeled. Palea keels wingless. Lodicules present; 2; free; membranous. Stamens 3. Anthers 2.5–5 mm long. Ovary hairy. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit small (2.5–3 mm long); longitudinally grooved; compressed dorsiventrally. Hilum long-linear (but at 1/3 of the grain length, shorter than in Arrhenatherum). Embryo small.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Microhairs presumably absent (see Zarco 1985). Costal silica bodies not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs (the ribs more prominent than in Arrhenatherum); with the ribs more or less constant in size (P. pallens), or with the ribs very irregular in sizes (P. longifolia). Midrib conspicuous to not readily distinguishable; with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles (P. longifolium), or not all bundle-associated (P. pallens). The ‘extra’ sclerenchyma of P. pallens in a continuous abaxial layer.
Cytology. Chromosome base number, x = 7. 2n = 14 (+/- 1B). 2 ploid.
Taxonomy. Pooideae; Poodae; Aveneae.
Distribution, ecology, phytogeography. 2 species; western Europe. Species of open habitats. In dry grassland, calcicole.
Holarctic. Boreal and Tethyan. Euro-Siberian. Mediterranean. European.
References, etc. Morphological/taxonomic: Zarco 1985. Leaf anatomical: Zarco 1985.
Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘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.’ http://biodiversity.uno.edu/delta/. Version: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).